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Message-ID: <yrdh2fmzgqlrfe35wvxb3a2z7wdqod3liupdbriqzc5ihqjw5y@fsqeyi34cbgg>
Date: Wed, 7 May 2025 17:11:01 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: tip-bot2 for Rong Xu <tip-bot2@...utronix.de>
Cc: linux-tip-commits@...r.kernel.org, Rong Xu <xur@...gle.com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] objtool: Speed up SHT_GROUP reindexing
>From 2a33e583c87e3283706f346f9d59aac20653b7fd Mon Sep 17 00:00:00 2001
Message-ID: <2a33e583c87e3283706f346f9d59aac20653b7fd.1746662991.git.jpoimboe@...nel.org>
From: Josh Poimboeuf <jpoimboe@...nel.org>
Date: Wed, 7 May 2025 16:56:55 -0700
Subject: [PATCH] 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: 2cb291596e2c ("objtool: Fix up st_info in COMDAT group section")
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
tools/objtool/elf.c | 47 ++++++++++++++++++-----------
tools/objtool/include/objtool/elf.h | 1 +
2 files changed, 30 insertions(+), 18 deletions(-)
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 8dffe68d705c..ca5d77db692a 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -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;
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index c7c4e87ebe88..0a2fa3ac0079 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -72,6 +72,7 @@ struct symbol {
u8 ignore : 1;
struct list_head pv_target;
struct reloc *relocs;
+ struct section *group_sec;
};
struct reloc {
--
2.49.0
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