Commit 4ed9d82b authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Peter Zijlstra
Browse files

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: 2cb29159 ("objtool: Fix up st_info in COMDAT group section")
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: default avatarRong Xu <xur@google.com>
Link: https://lkml.kernel.org/r/2a33e583c87e3283706f346f9d59aac20653b7fd.1746662991.git.jpoimboe@kernel.org
parent 2cb29159

tools/objtool/elf.c

+29 −18
Original line number Diff line number Diff line
@@ -572,28 +572,32 @@ static int read_symbols(struct elf *elf) 
	return -1;

}



/*

 * @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)

static int mark_group_syms(struct elf *elf)

{

	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) {

		if (sec->sh.sh_type != SHT_GROUP)

			continue;

		if (sec->sh.sh_link == symtab_idx &&

		    sec->sh.sh_info == old_idx) {

			sec->sh.sh_info = new_idx;

			mark_sec_changed(elf, sec, true);

			/*

			 * Each ELF group should have a unique symbol key.

			 * Return early on match.

			 */

			return;

		if (sec->sh.sh_type == SHT_GROUP &&

		    sec->sh.sh_link == symtab->idx) {

			sym = find_symbol_by_index(elf, sec->sh.sh_info);

			if (!sym) {

				ERROR("%s: can't find SHT_GROUP signature symbol",

				      sec->name);

				return -1;

			}



			sym->group_sec = sec;

		}

	}



	return 0;

}



/*
@@ -787,7 +791,11 @@ __elf_create_symbol(struct elf *elf, struct symbol *sym) 
		if (elf_update_sym_relocs(elf, old))

			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;

	}
@@ -1060,6 +1068,9 @@ struct elf *elf_open_read(const char *name, int flags) 
	if (read_symbols(elf))

		goto err;



	if (mark_group_syms(elf))

		goto err;



	if (read_relocs(elf))

		goto err;

tools/objtool/include/objtool/elf.h

+1 −0
Original line number Diff line number Diff line
@@ -72,6 +72,7 @@ struct symbol { 
	u8 ignore	     : 1;

	struct list_head pv_target;

	struct reloc *relocs;

	struct section *group_sec;

};



struct reloc {