.TH GELF_UPDATE_SYMSHNDX 3 2025-12-30 "Libelf" "Libelf Programmer's Manual"

.SH NAME
gelf_update_symshndx \- Update class\-independent symbol information and
extended section index in symbol table

.SH SYNOPSIS
.nf
.B #include <gelf.h>

.BI "int gelf_update_symshndx (Elf_Data *" symdata ", Elf_Data *" shndxdata ", int " ndx ", GElf_Sym *" sym ", Elf32_Word " xshndx ");"

.SH DESCRIPTION
This function updates
.I symdata
and
.IR shndxdata ,
at index
.I ndx
with the class\-independent symbol information from
.I sym
and the section index
.IR xshndx .
.I symdata
should be an
.B Elf_Data
pointer for an
.B SHT_SYMTAB
or
.B SHT_DYNSYM
section and
.I shndxdata
should be an
.B Elf_Data
pointer for an
.B SHT_SYMTAB_SHNDX
section.

The number of symbols in the symbol table can be calculated by dividing the
size of
.I symdata
by the size of a symbol table entry.
The size of
.I symdata
can be obtained from
.I symdata->d_size
or from the corresponding section header's
.BR sh_size .
The size of a symbol table entry can be obtained from
.BR gelf_fsize ()
with
.B ELF_T_SYM
or from the corresponding section header's
.BR sh_entsize .

A
.B SHT_SYMTAB_SHNDX
section is present in ELF binaries when the number of sections is too large to
be represented as an unsigned 16-bit value.  In this case the
.B st_shndx
field of a
.B GElf_Sym
will be set to
.B SHN_XINDEX
to indicate that the symbol's section index can be found in the
.B SHT_SYMTAB_SHNDX
section.
.I shndxdata
for this section can be acquired using
.BR elf_scnshndx (3),
.BR elf_getscn (3),
and
.BR elf_getdata (3).
The number of entries in
.I shndxdata
must be equal to the number of entries in
.IR symdata .
Entry
.I ndx
in
.I shndxdata
corresponds to entry
.I ndx
in
.IR symdata .

.SH PARAMETERS
.TP
.I symdata
Pointer to
.B Elf_Data
for a section with type
.B SHT_SYMTAB
or
.BR SHT_DYNSYM .

.TP
.I shndxdata
Pointer to
.B Elf_Data
for a section with type
.BR SHT_SYMTAB_SHNDX .
.I shndxdata
may be NULL.  If
.I shndxdata
is NULL, then
.I xshndx
must be zero.

.TP
.I ndx
Zero\-based index of the symbol table entry and extended section index entry
to be updated.

.TP
.I sym
Pointer to a caller\-provided symbol table entry.  For
.B ELFCLASS32
binaries,
.B st_value
and
.B st_size
should be able to fit within unsigned 32-bit values.
.I sym
must not be NULL.

.TP
.I xshndx
Updated extended section index entry to be associated with
.IR sym .
Must be zero if
.I shndxdata
is NULL.  If
.I sym->st_shndx
is not
.B SHN_XINDEX
then
.I xshndx
should be
.BR SHN_UNDEF .

.SH RETURN VALUE
On success, a non-zero value is returned and the entries at index
.I ndx
in
.I symdata
and
.I shndxdata
(if not NULL)
are updated with
.I sym
and
.IR xshndx ,
respectively.  The sections associated with
.I symdata
and
.I shndxdata
are flagged with
.BR ELF_F_DIRTY .
On failure, zero is returned, elf_errno is set.  If
.I sym
is NULL, then NULL is returned without setting elf_errno.

.SH SEE ALSO
.BR elf_getdata (3),
.BR elf_getscn (3),
.BR elf_scnshndx (3),
.BR gelf_fsize (3),
.BR gelf_getsymshndx (3),
.BR gelf_update_sym (3),
.BR libelf (3),
.BR elf (5)

.SH ATTRIBUTES
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR gelf_update_symshndx ()
T}	Thread safety	MT-Safe
.TE

.SH REPORTING BUGS
Report bugs to <elfutils-devel@sourceware.org> or https://sourceware.org/bugzilla/.