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objtool: Improve reloc hash size guestimate

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Nathan reported that LLVM ThinLTO builds have a performance regression
with commit 25cf0d8aa2 ("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: 25cf0d8aa2 ("objtool: Rewrite hashtable sizing")
Reported-by: Nathan Chancellor <nathan@kernel.org>
Debugged-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lkml.kernel.org/r/YMJpGLuGNsGtA5JJ@hirez.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra 2021-06-11 08:33:36 +02:00
parent c199f64ff9
commit d33b9035e1
2 changed files with 5 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
tools/objtool/elf.c
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@ -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) {

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

@ -83,6 +83,7 @@ struct elf {
int fd;
bool changed;
char *name;
unsigned int text_size;
struct list_head sections;
int symbol_bits;