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elf.5: Document compressed section headers

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Reviewed by:	emaste
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D33138
This commit is contained in:
Mark Johnston 2021-11-29 13:51:50 -05:00
parent 9ff084f0fa
commit e0189cf66a
1 changed files with 48 additions and 1 deletions
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49
share/man/man5/elf.5
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@ -24,7 +24,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd March 11, 2020
.Dd November 27, 2021
.Dt ELF 5
.Os
.Sh NAME
@ -795,6 +795,8 @@ The section contains executable machine instructions.
.It Dv SHF_MASKPROC
All bits included in this mask are reserved for processor-specific
semantics.
.It Dv SHF_COMPRESSED
The section data is compressed.
.El
.Pp
.It Dv sh_addr
@ -1069,6 +1071,50 @@ be registered.
This section holds information used for C++ exception-handling.
.El
.Pp
A section with the
.Dv SHF_COMPRESSED
flag set contains a compressed copy of the section data.
Compressed section data begins with an
.Vt Elf64_Chdr
or
.Vt Elf32_Chdr structure
which encodes the compression algorithm and some characteristics of the
uncompressed data.
.Bd -literal -offset indent
typedef struct {
Elf32_Word ch_type;
Elf32_Word ch_size;
Elf32_Word ch_addralign;
} Elf32_Chdr;
.Ed
.Bd -literal -offset indent
typedef struct {
Elf64_Word ch_type;
Elf64_Word ch_reserved;
Elf64_Xword ch_size;
Elf64_Xword ch_addralign;
} Elf64_Chdr;
.Ed
.Pp
.Bl -tag -width "ch_addralign" -compact
.It Dv ch_type
The compression algorithm used.
A value of
.Dv ELFCOMPRESS_ZLIB
indicates that the data is compressed using
.Xr zlib 3 .
.It Dv ch_size
The size, in bytes, of the uncompressed section data.
This corresponds to the
.Sy sh_size
field of a section header containing uncompressed data.
.It Dv ch_addralign
The address alignment of the uncompressed section data.
This corresponds to the
.Sy sh_addralign
field of a section header containing uncompressed data.
.El
.Pp
String table sections hold null-terminated character sequences, commonly
called strings.
The object file uses these strings to represent symbol
@ -1342,6 +1388,7 @@ writeable and executable.
.Xr objdump 1 ,
.Xr readelf 1 ,
.Xr execve 2 ,
.Xr zlib 3 ,
.Xr ar 5 ,
.Xr core 5
.Rs