freebsd-nq/contrib/elftoolchain/libelf/gelf_getchdr.3
Ed Maste 573456a931 libelf: add compression header support
GNU and Oracle libelf implementations added support for section
compression, intended to reduce the size of DWARF debug info (which
might be an order of magnitude larger than the code).

There are two compressed ELF section formats:

1. Old GNU - sections are renmaed to start with 'z'.  Section contains
   a magic number, uncompressed size, and compressed data.

2. Oracle and New GNU - compressed sections use the SHF_COMPRESSED flag.
   The compression header contains the compression type, uncompressed
   size, and uncompressed alignment.

The second style is preferred and this change implements only that one.

Submitted by:	Tiger Gao <tig@FreeBSDFoundation.org>
Reviewed by:	markj
MFC after:	2 weeks
Relnotes:	Yes
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D24566
2020-10-23 16:35:23 +00:00

118 lines
3.2 KiB
Groff

.\" SPDX-License-Identifier: BSD-2-Clause
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.\" $Id: gelf_getchdr.3 3639 2020-10-20 16:07:02Z tig $
.\"
.Dd October 23, 2020
.Dt GELF_GETCHDR 3
.Os
.Sh NAME
.Nm elf32_getchdr ,
.Nm elf64_getchdr ,
.Nm gelf_getchdr
.Nd retrieve the compression header of a section
.Sh LIBRARY
.Lb libelf
.Sh SYNOPSIS
.In libelf.h
.Ft "Elf32_Chdr *"
.Fn elf32_getchdr "Elf_Scn *s"
.Ft "Elf64_Chdr *"
.Fn elf64_getchdr "Elf_Scn *s"
.In gelf.h
.Ft "GElf_Chdr *"
.Fn gelf_getchdr "Elf_Scn *scn" "GElf_Chdr *chdr"
.Sh DESCRIPTION
These functions return a pointer to the ELF Compression Header data
structure associated with section descriptor
.Ar scn .
.Pp
Function
.Fn elf32_getchdr
retrieves a pointer to an
.Vt Elf32_Chdr
structure.
Section descriptor
.Ar scn
must be associated with an ELF descriptor of class
.Dv ELFCLASS32 .
.Pp
Function
.Fn elf64_getchdr
retrieves a pointer to an
.Vt Elf64_Chdr
structure.
Section descriptor
.Ar scn
must be associated with an ELF descriptor of class
.Dv ELFCLASS64 .
.Pp
Function
.Fn gelf_getchdr
copies the values in the compression header associated with argument
.Ar scn
to the structure pointed to be argument
.Ar dst .
The
.Vt GElf_Chdr
data structure is described in
.Xr gelf 3 .
.Sh RETURN VALUES
Functions
.Fn elf32_getchdr
and
.Fn elf64_getchdr
return a valid pointer to the appropriate compression header on success
or NULL if an error was encountered.
.Pp
Function
.Fn gelf_getchdr
returns argument
.Ar dst
if successful, or NULL if an error was encountered.
.Sh ERRORS
These functions may fail with the following errors:
.Bl -tag -width "[ELF_E_RESOURCE]"
.It Bq Er ELF_E_INVALID_SECTION_FLAGS
Arguments
.Ar scn
has invalid flags.
.It Bq Er ELF_E_INVALID_SECTION_TYPE
Argument
.Ar scn
has invalid type.
.It Bq Er ELF_E_NOT_COMPRESSED
Argument
.Ar scn
is not compressed.
.El
.Sh SEE ALSO
.Xr elf 3 ,
.Xr elf_getscn 3 ,
.Xr gelf 3 ,