The following commit has been merged into the objtool/core branch of tip: Commit-ID: d33b9035e14a35f6f2a5f067f0b156a93581811d Gitweb: https://git.kernel.org/tip/d33b9035e14a35f6f2a5f067f0b156a93581811d Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx> AuthorDate: Fri, 11 Jun 2021 08:33:36 +02:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Mon, 14 Jun 2021 14:05:36 +02:00 objtool: Improve reloc hash size guestimate Nathan reported that LLVM ThinLTO builds have a performance regression with commit 25cf0d8aa2a3 ("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: 25cf0d8aa2a3 ("objtool: Rewrite hashtable sizing") Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx> Debugged-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx> Link: https://lkml.kernel.org/r/YMJpGLuGNsGtA5JJ@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx --- tools/objtool/elf.c | 11 ++++------- tools/objtool/include/objtool/elf.h | 1 + 2 files changed, 5 insertions(+), 7 deletions(-) diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c index a8a0ee2..2371ccc 100644 --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -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) { diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h index 9008275..e343950 100644 --- a/tools/objtool/include/objtool/elf.h +++ b/tools/objtool/include/objtool/elf.h @@ -83,6 +83,7 @@ struct elf { int fd; bool changed; char *name; + unsigned int text_size; struct list_head sections; int symbol_bits;
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