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objtool: Speed up SHT_GROUP reindexing 

After elf_update_group_sh_info() was introduced, a prototype version of
"objtool klp diff" went from taking ~1s to several minutes, due to
looping almost endlessly in elf_update_group_sh_info() while creating
thousands of local symbols in a file with thousands of sections.

Dramatically improve the performance by marking all symbols' correlated
SHT_GROUP sections while reading the object.  That way there's no need
to search for it every time a symbol gets reindexed.

Fixes: 2cb291596e ("objtool: Fix up st_info in COMDAT group section")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Rong Xu <xur@google.com>
Link: https://lkml.kernel.org/r/2a33e583c87e3283706f346f9d59aac20653b7fd.1746662991.git.jpoimboe@kernel.org
This commit is contained in:
Josh Poimboeuf 2025-05-07 16:56:55 -07:00 committed by Peter Zijlstra
parent 2cb291596e
commit 4ed9d82bf5
2 changed files with 30 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

47
tools/objtool/elf.c
View File

@ -572,28 +572,32 @@ err:
return -1; return -1;
} }
/* static int mark_group_syms(struct elf *elf)
* @sym's idx has changed. Update the sh_info in group sections.
*/
static void elf_update_group_sh_info(struct elf *elf, Elf32_Word symtab_idx,
Elf32_Word new_idx, Elf32_Word old_idx)
{ {
struct section *sec; struct section *symtab, *sec;
struct symbol *sym;
symtab = find_section_by_name(elf, ".symtab");
if (!symtab) {
ERROR("no .symtab");
return -1;
}
list_for_each_entry(sec, &elf->sections, list) { list_for_each_entry(sec, &elf->sections, list) {
if (sec->sh.sh_type != SHT_GROUP) if (sec->sh.sh_type == SHT_GROUP &&
continue; sec->sh.sh_link == symtab->idx) {
if (sec->sh.sh_link == symtab_idx && sym = find_symbol_by_index(elf, sec->sh.sh_info);
sec->sh.sh_info == old_idx) { if (!sym) {
sec->sh.sh_info = new_idx; ERROR("%s: can't find SHT_GROUP signature symbol",
mark_sec_changed(elf, sec, true); sec->name);
/* return -1;
* Each ELF group should have a unique symbol key. }
* Return early on match.
*/ sym->group_sec = sec;
return;
} }
} }
return 0;
} }
/* /*
@ -787,7 +791,11 @@ __elf_create_symbol(struct elf *elf, struct symbol *sym)
if (elf_update_sym_relocs(elf, old)) if (elf_update_sym_relocs(elf, old))
return NULL; return NULL;
elf_update_group_sh_info(elf, symtab->idx, new_idx, first_non_local); if (old->group_sec) {
old->group_sec->sh.sh_info = new_idx;
mark_sec_changed(elf, old->group_sec, true);
}
new_idx = first_non_local; new_idx = first_non_local;
} }
@ -1060,6 +1068,9 @@ struct elf *elf_open_read(const char *name, int flags)
if (read_symbols(elf)) if (read_symbols(elf))
goto err; goto err;
if (mark_group_syms(elf))
goto err;
if (read_relocs(elf)) if (read_relocs(elf))
goto err; goto err;

1
tools/objtool/include/objtool/elf.h
View File

@ -72,6 +72,7 @@ struct symbol {
u8 ignore : 1; u8 ignore : 1;
struct list_head pv_target; struct list_head pv_target;
struct reloc *relocs; struct reloc *relocs;
struct section *group_sec;
}; };
struct reloc { struct reloc {