Added link.5 man page and updated a.out.5 manpage to reflect the new
code. Obtained from: NetBSD
This commit is contained in:
Nate Williams
parent
1603af0d3b
commit
b35481d443
@ -2,9 +2,9 @@
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#MISSING: dump.5 plot.5
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MAN5= a.out.5 acct.5 core.5 dir.5 disktab.5 fs.5 fbtab.5 fstab.5 \
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group.5 hosts.5 networks.5 passwd.5 phones.5 printcap.5 procfs.5 \
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protocols.5 remote.5 resolver.5 services.5 shells.5 stab.5 types.5 \
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utmp.5
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group.5 hosts.5 link.5 networks.5 passwd.5 phones.5 printcap.5 \
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procfs.5 protocols.5 remote.5 resolver.5 services.5 shells.5 \
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stab.5 types.5 utmp.5
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MLINKS= fs.5 inode.5 utmp.5 wtmp.5
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clean depend lint tags:
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@ -33,6 +33,7 @@
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)a.out.5 8.1 (Berkeley) 6/5/93
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.\" $Id$
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.\"
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.Dd June 5, 1993
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.Dt A.OUT 5
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@ -86,8 +87,7 @@ Every binary file begins with an
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structure:
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.Bd -literal -offset indent
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struct exec {
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unsigned short a_mid;
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unsigned short a_magic;
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unsigned long a_midmag;
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unsigned long a_text;
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unsigned long a_data;
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unsigned long a_bss;
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@ -100,25 +100,43 @@ struct exec {
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.Pp
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The fields have the following functions:
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.Bl -tag -width a_trsize
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.It Fa a_mid
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Contains a bit pattern that
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identifies binaries that were built for
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certain sub-classes of an architecture
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.Pq Sq machine IDs
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or variants of the operating system on a given architecture.
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The kernel may not support all machine IDs
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on a given architecture.
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The
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.Fa a_mid
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field is not present on some architectures;
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in this case, the
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.Fa a_magic
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field has type
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.Em unsigned long .
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.It Fa a_magic
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Contains a bit pattern
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.Pq Sq magic number
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that uniquely identifies binary files
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.It Fa a_midmag
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This field is stored in host byte-order.
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It has a number of sub-components accessed by the macros
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.Dv N_GETFLAG() ,
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.Dv N_GETMID() , and
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.Dv N_GETMAGIC() ,
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and set by the macro
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.Dv N_SETMAGIC().
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.Pp
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The macro
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.Dv N_GETFLAG()
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returns a few flags:
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.Bl -tag -width EX_DYNAMIC
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.It Dv EX_DYNAMIC
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indicates that the executable requires the services of the run-time link editor.
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.It Dv EX_PIC
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indicates that the object contains position independent code. This flag is
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set by
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.Xr as 1
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when given the
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.Sq -k
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flag and is preserved by
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.Xr ld 1
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if necessary.
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.El
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.Pp
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If both EX_DYNAMIC and EX_PIC are set, the object file is a position indendent
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executable image (eg. a shared library), which is to be loaded into the
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process address space by the run-time link editor.
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.Pp
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The macro
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.Dv N_GETMID()
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returns the machine-id.
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This indicates which machine(s) the binary is intended to run on.
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.Pp
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.Dv N_GETMAGIC()
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specifies the magic number, which uniquely identifies binary files
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and distinguishes different loading conventions.
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The field must contain one of the following values:
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.Bl -tag -width ZMAGIC
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@ -194,7 +212,10 @@ struct relocation_info {
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r_pcrel : 1,
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r_length : 2,
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r_extern : 1,
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: 4;
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r_baserel : 1,
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r_jmptable : 1,
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r_relative : 1,
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r_copy : 1;
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};
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.Ed
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.Pp
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@ -237,7 +258,9 @@ bit is clear, the relocation is
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.Sq local ;
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the link editor updates the pointer to reflect
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changes in the load addresses of the various segments,
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rather than changes in the value of a symbol.
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rather than changes in the value of a symbol (except when
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.Fa r_baserel
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is also set (see below).
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In this case, the content of the
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.Fa r_symbolnum
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field is an
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@ -245,6 +268,26 @@ field is an
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value (see below);
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this type field tells the link editor
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what segment the relocated pointer points into.
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.It Fa r_baserel
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If set, the symbol, as identified by the
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.Fa r_symbolnum
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field, is to be relocated to an offset into the Global Offset Table.
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At run-time, the entry in the Global Offset Table at this offset is set to
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be the address of the symbol.
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.It Fa r_jmptable
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If set, the symbol, as identified by the
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.Fa r_symbolnum
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field, is to be relocated to an offset into the Procedure Linkage Table.
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.It Fa r_relative
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If set, this relocation is relative to the (run-time) load address of the
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image this object file is going to be a part of. This type of relocation
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only occurs in shared objects.
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.It Fa r_copy
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If set, this relocation record identifies a symbol whose contents should
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be copied to the location given in
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.Fa r_address.
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The copying is done by the run-time link-editor from a suitable data
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item in a shared object.
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.El
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.Pp
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Symbols map names to addresses (or more generally, strings to values).
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@ -346,7 +389,28 @@ such as
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the values are described in
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.Xr stab 5 .
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.It Fa n_other
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This field is currently unused.
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This field provides information on the nature of the symbol independent of
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the symbol's location in terms of segments as determined by the
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.Fa n_type
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field. Currently, the lower 4 bits of the
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.Fa n_other
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field hold one of two values:
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.Dv AUX_FUNC
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and
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.Dv AUX_OBJECT
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.Po
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see
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.Aq Pa link.h
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for their definitions
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.Pc .
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.Dv AUX_FUNC
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associates the symbol with a callable function, while
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.Dv AUX_OBJECT
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associates the symbol with data, irrespective of their locations in
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either the text or the data segment.
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This field is intended to be used by
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.Xr ld 1
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for the construction of dynamic executables.
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.It Fa n_desc
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Reserved for use by debuggers; passed untouched by the link editor.
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Different debuggers use this field for different purposes.
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@ -364,12 +428,16 @@ The length represents the size of the entire table in bytes,
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so its minimum value (or the offset of the first string)
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is always 4 on 32-bit machines.
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.Sh SEE ALSO
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.Xr as 1 ,
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.Xr gdb 1 ,
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.Xr ld 1 ,
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.Xr brk 2 ,
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.Xr execve 2 ,
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.Xr nlist 3 ,
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.Xr core 5 ,
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.Xr dbx 5 ,
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.Xr stab 5
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.Xr stab 5 ,
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.Xr link 5
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.Sh HISTORY
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The
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.Pa a.out.h
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@ -377,7 +445,7 @@ include file appeared in
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.At v7 .
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.Sh BUGS
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Since not all of the supported architectures use the
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.Fa a_mid
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.Fa a_midmag
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field,
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it can be difficult to determine what
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architecture a binary will execute on
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559
share/man/man5/link.5
Normal file
559
share/man/man5/link.5
Normal file
@ -0,0 +1,559 @@
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.\" Copyright (c) 1993 Paul Kranenburg
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by Paul Kranenburg.
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.\" 3. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $Id$
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.\"
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.Dd October 23, 1993
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.Dt LINK 5
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.Os
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.Sh NAME
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.Nm link
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.Nd dynamic loader and link editor interface
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.Sh SYNOPSIS
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.Fd #include <link.h>
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.Sh DESCRIPTION
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The include file
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.Aq Pa link.h
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declares several structures that are present in dynamically linked
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programs and libraries.
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The structures define the interface between several components of the
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link-editor and loader mechanism. The layout of a number of these
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structures within the binaries resembles the a.out format in many places
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as it serves such similar functions as symbol definitions (including the
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accompanying string table) and relocation records needed to resolve
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references to external entities. It also records a number of data structures
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unique to the dynamic loading and linking process. These include references
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to other objects that are required to complete the link-editing process and
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indirection tables to facilitate
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.Em Position Independent Code
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(PIC for short) to improve sharing of code pages among different processes.
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The collection of data structures described here will be refered to as the
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.Em Run-time Relocation Section (RRS)
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and is embedded in the standard text and data segments of the dynamically
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linked program or shared object image as the existing
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.Xr a.out
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format offers no room for it elsewhere.
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.Pp
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Several utilities cooperate to ensure that the task of getting a program
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ready to run can complete successfully in a way that optimizes the use
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of system resources. The compiler emits PIC code from which shared libraries
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can be build by
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.Xr ld 1.
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The compiler also includes size information of any initialized data items
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through the .size assembler directive. PIC code differs from conventional code
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in that it accesses data variables through an indirection table, the
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Global Offset Table, by convention accessable by the reserved name
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.Em _GLOBAL_OFFSET_TABLE_.
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The exact mechanism used for this is machine dependent, usually a machine
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register is reserved for the purpose. The rational behind this construct
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is to generate code that is independent of the actual load address. Only
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the values contained in the Global Offset Table may need updating at run-time
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depending on the load addresses of the various shared objects in the address
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space.
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.Pp
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Likewise, procedure calls to globally defined functions are redirected through
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the Procedure Linkage Table (PLT) residing in the data segment of the core
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image. Again, this is done to avoid run-time modifications to the text segment.
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.Pp
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The linker-editor allocates the Global Offset Table and Procedure Linkage Table
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when combining PIC object files into an image suitable for mapping into the
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process address space. It also collects all symbols that may be needed by the
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run-time link-editor and stores these along with the image's text and data bits.
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Another reserved symbol,
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.Em _DYNAMIC
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is used to indicate the presence of the run-time linker structures. Whenever
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_DYNAMIC is relocated to 0, there is no need to invoke the run-time
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link-editor. If this symbol is non-zero, it points at a data structure from
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which the location of the necessary relocation- and symbol information can
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be derived. This is most notably used by the start-up module,
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.Em crt0.
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The _DYNAMIC structure is conventionally located at the start of the data
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segment of the image to which it pertains.
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.Pp
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.Sh DATA STRUCTURES
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The data structures supporting dynamic linking and run-time relocation
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reside both in the text and data segments of the image they apply to.
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The text segments contain read-only data such as symbols descriptions and
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names, while the data segments contain the tables that need to be modified by
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during the relocation process.
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.Pp
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The _DYNAMIC symbol references a
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.Fa _dynamic
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structure:
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.Bd -literal -offset indent
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struct _dynamic {
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int d_version;
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struct so_debug *d_debug;
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union {
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struct section_dispatch_table *d_sdt;
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} d_un;
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struct ld_entry *d_entry;
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};
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.Ed
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.Bl -tag -width d_version
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.It Fa d_version
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This field provides for different versions of the dynamic linking
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implementation. The current version numbers understood by ld and ld.so are
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.Em LD_VERSION_SUN (3),
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which is used by the SunOS 4.x releases, and
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.Em LD_VERSION_BSD (8),
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which is currently in use by FreeBSD since release 1.1.
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.It Fa d_un
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Refers to a
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.Em d_version
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dependent data structure.
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.It Fa so_debug
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this field provides debuggers with a hook to access symbol tables of shared
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objects loaded as a result of the actions of the run-time link-editor.
|
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.El
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.Pp
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The
|
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.Fa section_dispatch_table
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structure is the main
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.Dq dispatcher
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table, containing offsets into the image's segments where various symbol
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and relocation information is located.
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.Bd -literal -offset indent
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struct section_dispatch_table {
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struct so_map *sdt_loaded;
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long sdt_sods;
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long sdt_filler1;
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long sdt_got;
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long sdt_plt;
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long sdt_rel;
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long sdt_hash;
|
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long sdt_nzlist;
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long sdt_filler2;
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long sdt_buckets;
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long sdt_strings;
|
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long sdt_str_sz;
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long sdt_text_sz;
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long sdt_plt_sz;
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};
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.Ed
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.Pp
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.Bl -tag -width sdt_filler1
|
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.It Fa sdt_loaded
|
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A pointer to the first link map loaded (see below). This field is set by
|
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.Xr ld.so.
|
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.It Fa sdt_sods
|
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The start of a (linked) list of shared object descriptors needed by
|
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.Em this
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object.
|
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.It Fa sdt_filler1
|
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Depricated (used by SunOS to specify library search rules).
|
||||
.It Fa sdt_got
|
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The location of the Global Offset Table within this image.
|
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.It Fa sdt_plt
|
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The location of the Procedure Linkage Table within this image.
|
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.It Fa sdt_rel
|
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The location of an array of
|
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.Fa relocation_info
|
||||
structures
|
||||
.Po
|
||||
see
|
||||
.Xr a.out 5
|
||||
.Pc
|
||||
specifying run-time relocations.
|
||||
.It Fa sdt_hash
|
||||
The location of the hash table for fast symbol lookup in this object's
|
||||
symbol table.
|
||||
.It Fa sdt_nzlist
|
||||
The location of the symbol table.
|
||||
.It Fa sdt_filler2
|
||||
Currently unused.
|
||||
.It Fa sdt_buckets
|
||||
The number of buckets in
|
||||
.Fa sdt_hash
|
||||
.It Fa sdt_strings
|
||||
The location of the symbol string table that goes with
|
||||
.Fa sdt_nzlist.
|
||||
.It Fa sdt_str_sz
|
||||
The size of the string table.
|
||||
.It Fa sdt_text_sz
|
||||
The size of the object's text segment.
|
||||
.It Fa sdt_plt_sz
|
||||
The size of the Procedure Linkage Table.
|
||||
.El
|
||||
.Pp
|
||||
A
|
||||
.Fa sod
|
||||
structure descibes a shared object that is needed
|
||||
to complete the link edit process of the object containing it.
|
||||
A list of such objects
|
||||
.Po
|
||||
chained through
|
||||
.Fa sod_next
|
||||
.Pc
|
||||
is pointed at
|
||||
by the
|
||||
.Fa sdt_sods
|
||||
in the section_dispatch_table structure.
|
||||
.Bd -literal -offset indent
|
||||
struct sod {
|
||||
long sod_name;
|
||||
u_int sod_library : 1,
|
||||
sod_unused : 31;
|
||||
short sod_major;
|
||||
short sod_minor;
|
||||
long sod_next;
|
||||
};
|
||||
.Ed
|
||||
.Pp
|
||||
.Bl -tag -width sod_library
|
||||
.It Fa sod_name
|
||||
The offset in the text segment of a string describing this link object.
|
||||
.It Fa sod_library
|
||||
If set,
|
||||
.Fa sod_name
|
||||
specifies a library that is to be searched for by ld.so. The path name
|
||||
is obtained by searching a set of directories
|
||||
.Po
|
||||
see also
|
||||
.Xr ldconfig 8
|
||||
.Pc
|
||||
for a shared object matching
|
||||
.Em lib\&<sod_name>\&.so.n.m.
|
||||
If not set,
|
||||
.Fa sod_name
|
||||
should point at a full path name for the desired shared object.
|
||||
.It Fa sod_major
|
||||
Specifies the major version number of the shared object to load.
|
||||
.It Fa sod_minor
|
||||
Specifies the prefered minor version number of the shared object to load.
|
||||
.El
|
||||
.Pp
|
||||
The run-time link-editor maintains a list of structures called
|
||||
.Em link maps
|
||||
to keep track of all shared objects loaded into a process' address space.
|
||||
These structures are only used at run-time and do not occur within
|
||||
the text or data segment of an executable or shared library.
|
||||
.Bd -literal -offset indent
|
||||
struct so_map {
|
||||
caddr_t som_addr;
|
||||
char *som_path;
|
||||
struct so_map *som_next;
|
||||
struct sod *som_sod;
|
||||
caddr_t som_sodbase;
|
||||
u_int som_write : 1;
|
||||
struct _dynamic *som_dynamic;
|
||||
caddr_t som_spd;
|
||||
};
|
||||
.Ed
|
||||
.Bl -tag -width som_dynamic
|
||||
.It Fa som_addr
|
||||
The address at which the shared object associated with this link map has
|
||||
been loaded.
|
||||
.It Fa som_path
|
||||
The full path name of the loaded object.
|
||||
.It Fa som_next
|
||||
Pointer to the next link map.
|
||||
.It Fa som_sod
|
||||
The
|
||||
.Fa sod
|
||||
structure that was responsible for loading this shared object.
|
||||
.It Fa som_sodbase
|
||||
Tossed in later versions the run-time linker.
|
||||
.It Fa som_write
|
||||
Set if (some portion of) this object's text segment is currently writable.
|
||||
.It Fa som_dynamic
|
||||
Pointer to this object's
|
||||
.Fa _dynamic
|
||||
structure.
|
||||
.It Fa som_spd
|
||||
Hook for attaching private data maintained by the run-time link-editor.
|
||||
.El
|
||||
.Pp
|
||||
Symbol description with size. This is simply an
|
||||
.Fa nlist
|
||||
structure with one field
|
||||
.Pq Fa nz_size
|
||||
added. Used to convey size information on items in the data segment
|
||||
of shared objects. An array of these lives in the shared object's
|
||||
text segment and is addressed by the
|
||||
.Fa sdt_nzlist
|
||||
field of
|
||||
.Fa section_dispatch_table.
|
||||
.Bd -literal -offset indent
|
||||
struct nzlist {
|
||||
struct nlist nlist;
|
||||
u_long nz_size;
|
||||
#define nz_un nlist.n_un
|
||||
#define nz_strx nlist.n_un.n_strx
|
||||
#define nz_name nlist.n_un.n_name
|
||||
#define nz_type nlist.n_type
|
||||
#define nz_value nlist.n_value
|
||||
#define nz_desc nlist.n_desc
|
||||
#define nz_other nlist.n_other
|
||||
};
|
||||
.Ed
|
||||
.Bl -tag -width nz_size
|
||||
.It Fa nlist
|
||||
.Po
|
||||
see
|
||||
.Xr nlist 5
|
||||
.Pc .
|
||||
.It Fa nz_size
|
||||
The size of the data represented by this symbol.
|
||||
.El
|
||||
.Pp
|
||||
A hash table is included within the text segment of shared object to
|
||||
to facilitate quick lookup of symbols during run-time link-editing.
|
||||
The
|
||||
.Fa sdt_hash
|
||||
field of the
|
||||
.Fa section_dispatch_table
|
||||
structure points at an array of
|
||||
.Fa rrs_hash
|
||||
structures:
|
||||
.Bd -literal -offset indent
|
||||
struct rrs_hash {
|
||||
int rh_symbolnum; /* symbol number */
|
||||
int rh_next; /* next hash entry */
|
||||
};
|
||||
.Ed
|
||||
.Pp
|
||||
.Bl -tag -width rh_symbolnum
|
||||
.It Fa rh_symbolnum
|
||||
The index of the symbol in the shared object's symbol table (as given by the
|
||||
.Fa ld_symbols
|
||||
field).
|
||||
.It Fa rh_next
|
||||
In case of collisions, this field is the offset of the next entry in this
|
||||
hash table bucket. It is zero for the last bucket element.
|
||||
.El
|
||||
The
|
||||
.Fa rt_symbol
|
||||
structure is used to keep track of run-time allocated commons
|
||||
and data items copied from shared objects. These items are kept on linked list
|
||||
and is exported through the
|
||||
.Fa dd_cc
|
||||
field in the
|
||||
.Fa so_debug
|
||||
structure (see below) for use by debuggers.
|
||||
.Bd -literal -offset indent
|
||||
struct rt_symbol {
|
||||
struct nzlist *rt_sp;
|
||||
struct rt_symbol *rt_next;
|
||||
struct rt_symbol *rt_link;
|
||||
caddr_t rt_srcaddr;
|
||||
struct so_map *rt_smp;
|
||||
};
|
||||
.Ed
|
||||
.Pp
|
||||
.Bl -tag -width rt_scraddr
|
||||
.It Fa rt_sp
|
||||
The symbol description.
|
||||
.It Fa rt_next
|
||||
Virtual address of next rt_symbol.
|
||||
.It Fa rt_link
|
||||
Next in hash bucket. Used by internally by ld.so.
|
||||
.It Fa rt_srcaddr
|
||||
Location of the source of initialized data within a shared object.
|
||||
.It Fa rt_smp
|
||||
The shared object which is the original source of the data that this
|
||||
run-time symbol describes.
|
||||
.El
|
||||
.Pp
|
||||
The
|
||||
.Fa so_debug
|
||||
structure is used by debuggers to gain knowledge of any shared objects
|
||||
that have been loaded in the process's address space as a result of run-time
|
||||
link-editing. Since the run-time link-editor runs as a part of process
|
||||
initialization, a debugger that wishes to access symbols from shared objects
|
||||
can only do so after the link-editor has been called from crt0.
|
||||
A dynamically linked binary contains a
|
||||
.Fa so_debug
|
||||
structure which can be located by means of the
|
||||
.Fa d_debug
|
||||
field in
|
||||
.Fa _dynamic.
|
||||
.Bd -literal -offset indent
|
||||
struct so_debug {
|
||||
int dd_version;
|
||||
int dd_in_debugger;
|
||||
int dd_sym_loaded;
|
||||
char *dd_bpt_addr;
|
||||
int dd_bpt_shadow;
|
||||
struct rt_symbol *dd_cc;
|
||||
};
|
||||
.Ed
|
||||
.Pp
|
||||
.Bl -tag -width dd_in_debugger
|
||||
.It Fa dd_version
|
||||
Version number of this interface.
|
||||
.It Fa dd_in_debugger
|
||||
Set by the debugger to indicate to the run-time linker that the program is
|
||||
run under control of a debugger.
|
||||
.It Fa dd_sym_loaded
|
||||
Set by the run-time linker whenever it adds symbols by loading shared objects.
|
||||
.It Fa dd_bpt_addr
|
||||
The address were a breakpoint will be set by the the run-time linker to
|
||||
divert control to the debugger. This address is determined by the start-up
|
||||
module,
|
||||
.Em crt0.o,
|
||||
to be some convenient place before the call to _main.<.It Fa dd_bpt_shadow
|
||||
Contains the original instruction that was at
|
||||
.Fa dd_bpt_addr.
|
||||
The debugger is expected to put this instruction back before continuing the
|
||||
program.
|
||||
.It Fa dd_cc
|
||||
A pointer to the linked list of run-time allocated symbols that the debugger
|
||||
may be interested in.
|
||||
.El
|
||||
.Pp
|
||||
The
|
||||
.Em ld_entry
|
||||
structure defines a set of service routines within ld.so. See
|
||||
.Xr libdl.a
|
||||
for more information.
|
||||
.Bd -literal -offset indent
|
||||
struct ld_entry {
|
||||
void *(*dlopen)(char *, int);
|
||||
int (*dlclose)(void *);
|
||||
void *(*dlsym)(void *, char *);
|
||||
int (*dlctl)(void *, int, void *);
|
||||
};
|
||||
.Ed
|
||||
|
||||
The
|
||||
.Fa crt_ldso
|
||||
structure defines the interface between the start-up code in crt0 and ld.so.
|
||||
.Bd -literal -offset indent
|
||||
struct crt_ldso {
|
||||
int crt_ba;
|
||||
int crt_dzfd;
|
||||
int crt_ldfd;
|
||||
struct _dynamic *crt_dp;
|
||||
char **crt_ep;
|
||||
caddr_t crt_bp;
|
||||
char *crt_prog;
|
||||
char *crt_ldso;
|
||||
};
|
||||
#define CRT_VERSION_SUN 1
|
||||
#define CRT_VERSION_BSD2 2
|
||||
#define CRT_VERSION_BSD3 3
|
||||
.Ed
|
||||
.Bl -tag -width crt_dzfd
|
||||
.It Fa crt_ba
|
||||
The virtual address at which ld.so was loaded by crt0.
|
||||
.It Fa crt_dzfd
|
||||
On SunOS systems, this field contains an open file descriptor to
|
||||
.Dq /dev/zero
|
||||
used to get demand paged zeroed pages. On FreeBSD systems it contains -1.
|
||||
.It Fa crt_ldfd
|
||||
Contains an open file descriptor that was used by crt0 to load ld.so.
|
||||
.It Fa crt_dp
|
||||
A pointer to main's
|
||||
.Fa _dynamic
|
||||
structure.
|
||||
.It Fa crt_ep
|
||||
A pointer to the environment strings.
|
||||
.It Fa crt_bp
|
||||
The address at which a breakpoint will be placed by the run-time linker
|
||||
if the main program is run by a debugger.
|
||||
See
|
||||
.Fa so_debug
|
||||
.It Fa crt_prog
|
||||
The name of the main program as determined by crt0 (CRT_VERSION_BSD3 only).
|
||||
.It Fa crt_ldso
|
||||
The path of the run-time linker as mapped by crt0 (CRT_VERSION_BSD4 only).
|
||||
.El
|
||||
.Pp
|
||||
The
|
||||
.Fa hints_header
|
||||
and
|
||||
.Fa hints_bucket
|
||||
structures define the layout of the library hints, normally found in
|
||||
.Dq /var/run/ld.so.hints,
|
||||
which is used by ld.so to quickly locate the shared object images in the
|
||||
filesystem.
|
||||
The organization of the hints file is not unlike that of an
|
||||
.Dq a.out
|
||||
object file, in that it contains a header determining the offset and size
|
||||
of a table of fixed sized hash buckets and a common string pool.
|
||||
.Bd -literal -offset indent
|
||||
struct hints_header {
|
||||
long hh_magic;
|
||||
#define HH_MAGIC 011421044151
|
||||
long hh_version;
|
||||
#define LD_HINTS_VERSION_1 1
|
||||
long hh_hashtab;
|
||||
long hh_nbucket;
|
||||
long hh_strtab;
|
||||
long hh_strtab_sz;
|
||||
long hh_ehints;
|
||||
};
|
||||
.Ed
|
||||
.Bl -tag -width hh_strtab_sz
|
||||
.It Fa hh_magic
|
||||
Hints file magic number.
|
||||
.It Fa hh_version
|
||||
Interface version number.
|
||||
.It Fa hh_hashtab
|
||||
Offset of hash table.
|
||||
.It Fa hh_strtab
|
||||
Offset of string table.
|
||||
.It Fa hh_strtab_sz
|
||||
Size of strings.
|
||||
.It Fa hh_ehints
|
||||
Maximum usable offset in hints file.
|
||||
.El
|
||||
.Pp
|
||||
.Bd -literal -offset indent
|
||||
/*
|
||||
* Hash table element in hints file.
|
||||
*/
|
||||
struct hints_bucket {
|
||||
int hi_namex;
|
||||
int hi_pathx;
|
||||
int hi_dewey[MAXDEWEY];
|
||||
int hi_ndewey;
|
||||
#define hi_major hi_dewey[0]
|
||||
#define hi_minor hi_dewey[1]
|
||||
int hi_next;
|
||||
};
|
||||
.Ed
|
||||
.Bl -tag -width hi_ndewey
|
||||
.It Fa hi_namex
|
||||
Index of the string identifying the library.
|
||||
.It Fa hi_pathx
|
||||
Index of the string representing the full path name of the library.
|
||||
.It Fa hi_dewey
|
||||
The version numbers of the shared library.
|
||||
.It Fa hi_ndewey
|
||||
The number of valid entries in
|
||||
.Fa hi_dewey.
|
||||
.It Fa hi_next
|
||||
Next bucket in case of hashing collisions.
|
||||
.El
|
||||
|
||||
.Sh CAVEATS
|
||||
Only the (GNU) C compiler currently supports the creation of shared libraries.
|
||||
Other programming languages can not be used.
|
||||
|
||||
Loading…
Reference in New Issue
Block a user