Commit d33b9035 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

objtool: Improve reloc hash size guestimate 



Nathan reported that LLVM ThinLTO builds have a performance regression
with commit 25cf0d8a ("objtool: Rewrite hashtable sizing"). Sami
was quick to note that this is due to their use of -ffunction-sections.

As a result the .text section is small and basing the number of relocs
off of that no longer works. Instead have read_sections() compute the
sum of all SHF_EXECINSTR sections and use that.

Fixes: 25cf0d8a ("objtool: Rewrite hashtable sizing")
Reported-by: default avatarNathan Chancellor <nathan@kernel.org>
Debugged-by: default avatarSami Tolvanen <samitolvanen@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: default avatarNathan Chancellor <nathan@kernel.org>
Link: https://lkml.kernel.org/r/YMJpGLuGNsGtA5JJ@hirez.programming.kicks-ass.net
parent c199f64f

tools/objtool/elf.c

+4 −7
Original line number Diff line number Diff line
@@ -288,6 +288,9 @@ static int read_sections(struct elf *elf) 
		}

		sec->len = sec->sh.sh_size;



		if (sec->sh.sh_flags & SHF_EXECINSTR)

			elf->text_size += sec->len;



		list_add_tail(&sec->list, &elf->sections);

		elf_hash_add(section, &sec->hash, sec->idx);

		elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
@@ -581,13 +584,7 @@ static int read_relocs(struct elf *elf) 
	unsigned int symndx;

	unsigned long nr_reloc, max_reloc = 0, tot_reloc = 0;



	sec = find_section_by_name(elf, ".text");

	if (!sec) {

		WARN("no .text");

		return -1;

	}



	if (!elf_alloc_hash(reloc, sec->len / 16))

	if (!elf_alloc_hash(reloc, elf->text_size / 16))

		return -1;



	list_for_each_entry(sec, &elf->sections, list) {

tools/objtool/include/objtool/elf.h

+1 −0
Original line number Diff line number Diff line
@@ -83,6 +83,7 @@ struct elf { 
	int fd;

	bool changed;

	char *name;

	unsigned int text_size;

	struct list_head sections;



	int symbol_bits;