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x86: Cache the symbol table when packing relative relocations

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When packing relative relocations, x86 linker may load the same symbol
table repeatedly, which can take a long time.  On Intel Core i7-1195G7
with 32GB RAM, it takes more than 45 minutes to create an output with
-pie -z pack-relative-relocs from an input with 208025 code sections.
Cache the symbol table to reduce the link time to less than 2 seconds.

On the same machine, creating 3.1GB clang executable in LLVM 21.1.3 debug
build:

user            55.39 seconds
system          6.71 seconds
total           65.80 seconds
maximum set(GB) 10.43
page faults     2406941

	PR ld/33765
	* elfxx-x86.c (elf_x86_relative_reloc_record_add): Remove
	keep_symbuf_p.
	(_bfd_x86_elf_link_relax_section): Updated.  Cache the symbol
	table to avoid loading it again.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
This commit is contained in:
H.J. Lu
2026-01-09 08:54:42 +08:00
parent 15a733414f
commit 4e007c6bff
1 changed files with 21 additions and 31 deletions
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52
bfd/elfxx-x86.c
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@@ -1011,7 +1011,7 @@ elf_x86_relative_reloc_record_add
struct elf_x86_relative_reloc_data *relative_reloc,
Elf_Internal_Rela *rel, asection *sec,
asection *sym_sec, struct elf_link_hash_entry *h,
Elf_Internal_Sym *sym, bfd_vma offset, bool *keep_symbuf_p)
Elf_Internal_Sym *sym, bfd_vma offset)
{
bfd_size_type newidx;
@@ -1055,8 +1055,6 @@ elf_x86_relative_reloc_record_add
{
relative_reloc->data[newidx].sym = sym;
relative_reloc->data[newidx].u.sym_sec = sym_sec;
/* We must keep the symbol buffer since SYM will be used later. */
*keep_symbuf_p = true;
}
relative_reloc->data[newidx].offset = offset;
relative_reloc->data[newidx].address = 0;
@@ -1079,7 +1077,7 @@ _bfd_x86_elf_link_relax_section (bfd *abfd ATTRIBUTE_UNUSED,
Elf_Internal_Shdr *symtab_hdr;
Elf_Internal_Rela *internal_relocs;
Elf_Internal_Rela *irel, *irelend;
Elf_Internal_Sym *isymbuf = NULL;
Elf_Internal_Sym *isymbuf;
struct elf_link_hash_entry **sym_hashes;
elf_backend_data *bed;
struct elf_x86_link_hash_table *htab;
@@ -1087,7 +1085,6 @@ _bfd_x86_elf_link_relax_section (bfd *abfd ATTRIBUTE_UNUSED,
bool is_x86_64;
bool unaligned_section;
bool return_status = false;
bool keep_symbuf = false;
/* Assume we're not going to change any sizes, and we'll only need
one pass. */
@@ -1131,6 +1128,23 @@ _bfd_x86_elf_link_relax_section (bfd *abfd ATTRIBUTE_UNUSED,
if (internal_relocs == NULL)
return false;
isymbuf = (Elf_Internal_Sym *) symtab_hdr->contents;
if (isymbuf == NULL && symtab_hdr->sh_info > 1)
{
/* symtab_hdr->sh_info == the number of local symbols + 1. Load
the symbol table if there are local symbols. */
isymbuf = bfd_elf_get_elf_syms (abfd, symtab_hdr,
symtab_hdr->sh_info,
0, NULL, NULL, NULL);
if (isymbuf == NULL)
return false;
/* Cache the symbol table to avoid loading the same symbol table
repeatedly which can take a long time if the input has many
code sections. */
symtab_hdr->contents = (unsigned char *) isymbuf;
}
irelend = internal_relocs + input_section->reloc_count;
for (irel = internal_relocs; irel < irelend; irel++)
{
@@ -1163,20 +1177,6 @@ _bfd_x86_elf_link_relax_section (bfd *abfd ATTRIBUTE_UNUSED,
if (r_symndx < symtab_hdr->sh_info)
{
/* Read this BFD's local symbols. */
if (isymbuf == NULL)
{
isymbuf = (Elf_Internal_Sym *) symtab_hdr->contents;
if (isymbuf == NULL)
{
isymbuf = bfd_elf_get_elf_syms (abfd, symtab_hdr,
symtab_hdr->sh_info,
0, NULL, NULL, NULL);
if (isymbuf == NULL)
goto error_return;
}
}
isym = isymbuf + r_symndx;
switch (isym->st_shndx)
{
@@ -1278,8 +1278,7 @@ _bfd_x86_elf_link_relax_section (bfd *abfd ATTRIBUTE_UNUSED,
if (!elf_x86_relative_reloc_record_add (info,
&htab->relative_reloc,
irel, htab->elf.sgot,
sec, h, isym, offset,
&keep_symbuf))
sec, h, isym, offset))
goto error_return;
continue;
@@ -1348,8 +1347,7 @@ _bfd_x86_elf_link_relax_section (bfd *abfd ATTRIBUTE_UNUSED,
((unaligned_section || unaligned_offset)
? &htab->unaligned_relative_reloc
: &htab->relative_reloc),
irel, input_section, sec, h, isym, offset,
&keep_symbuf))
irel, input_section, sec, h, isym, offset))
goto error_return;
}
}
@@ -1359,14 +1357,6 @@ _bfd_x86_elf_link_relax_section (bfd *abfd ATTRIBUTE_UNUSED,
return_status = true;
error_return:
if ((unsigned char *) isymbuf != symtab_hdr->contents)
{
/* Cache the symbol buffer if it must be kept. */
if (keep_symbuf)
symtab_hdr->contents = (unsigned char *) isymbuf;
else
free (isymbuf);
}
if (elf_section_data (input_section)->relocs != internal_relocs)
free (internal_relocs);
return return_status;