diff options
| author | Josh Poimboeuf <jpoimboe@kernel.org> | 2025-11-20 12:52:15 -0800 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2025-11-21 10:04:07 +0100 |
| commit | 024020e2b6adb4e568fb80f624b5e20d8943f107 (patch) | |
| tree | 558d3035bbf5eeb3d43c5a8a2b0632ef73d285c7 | |
| parent | 2092007aa32f8dd968c38751bd1b7cac9b1f738d (diff) | |
objtool: Support Clang AUTOFDO .cold functions
AutoFDO enables -fsplit-machine-functions which can move the cold parts
of a function to a <func>.cold symbol in a .text.split.<func> section.
Unlike GCC, the Clang <func>.cold symbols are not marked STT_FUNC. This
confuses objtool in several ways, resulting in warnings like the
following:
vmlinux.o: warning: objtool: apply_retpolines.cold+0xfc: unsupported instruction in callable function
vmlinux.o: warning: objtool: machine_check_poll.cold+0x2e: unsupported instruction in callable function
vmlinux.o: warning: objtool: free_deferred_objects.cold+0x1f: relocation to !ENDBR: free_deferred_objects.cold+0x26
vmlinux.o: warning: objtool: rpm_idle.cold+0xe0: relocation to !ENDBR: rpm_idle.cold+0xe7
vmlinux.o: warning: objtool: tcp_rcv_state_process.cold+0x1c: relocation to !ENDBR: tcp_rcv_state_process.cold+0x23
Fix it by marking the .cold symbols as STT_FUNC.
Fixes: 2fd65f7afd5a ("AutoFDO: Enable machine function split optimization for AutoFDO")
Closes: https://lore.kernel.org/20251103215244.2080638-2-xur@google.com
Reported-by: Rong Xu <xur@google.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: xur@google.com
Tested-by: xur@google.com
Link: https://patch.msgid.link/20a67326f04b2a361c031b56d58e8a803b3c5893.1763671318.git.jpoimboe@kernel.org
| -rw-r--r-- | tools/objtool/elf.c | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c index 3f20b257ab25..7895f65aca2a 100644 --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -502,8 +502,16 @@ static int elf_add_symbol(struct elf *elf, struct symbol *sym) if (strstarts(sym->name, ".klp.sym")) sym->klp = 1; - if (!sym->klp && is_func_sym(sym) && strstr(sym->name, ".cold")) + if (!sym->klp && !is_sec_sym(sym) && strstr(sym->name, ".cold")) { sym->cold = 1; + + /* + * Clang doesn't mark cold subfunctions as STT_FUNC, which + * breaks several objtool assumptions. Fake it. + */ + sym->type = STT_FUNC; + } + sym->pfunc = sym->cfunc = sym; sym->demangled_name = demangle_name(sym); |