Re: [PATCH v6 22/25] x86/asm: annotate indirect jumps

Josh Poimboeuf
2020-10-21T21:28:07Z

On Wed, Oct 21, 2020 at 11:32:13AM +0200, Peter Zijlstra wrote:
> On Wed, Oct 21, 2020 at 10:56:06AM +0200, Peter Zijlstra wrote:
>
> > I do not see these in particular, although I do see a lot of:
> >
> > "sibling call from callable instruction with modified stack frame"
>
> defconfig-build/vmlinux.o: warning: objtool: msr_write()+0x10a: sibling call from callable instruction with modified stack frame
> defconfig-build/vmlinux.o: warning: objtool: msr_write()+0x99: (branch)
> defconfig-build/vmlinux.o: warning: objtool: msr_write()+0x3e: (branch)
> defconfig-build/vmlinux.o: warning: objtool: msr_write()+0x0: <=== (sym)
>
> $ nm defconfig-build/vmlinux.o | grep msr_write
> 0000000000043250 t msr_write
> 00000000004289c0 T msr_write
> 0000000000003056 t msr_write.cold
>
> Below 'fixes' it. So this is also caused by duplicate symbols.

There's a new linker flag for renaming duplicates:

https://sourceware.org/bugzilla/show_bug.cgi?id=26391

But I guess that doesn't help us now.

I don't have access to GCC 10 at the moment so I can't recreate it.
Does this fix it?

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 4e1d7460574b..aecdf25b2381 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -217,11 +217,14 @@ struct symbol *find_func_containing(struct section *sec, unsigned long offset)
return NULL;
}

+#define for_each_possible_sym(elf, name, sym) \
+ elf_hash_for_each_possible(elf->symbol_name_hash, sym, name_hash, str_hash(name))
+
struct symbol *find_symbol_by_name(const struct elf *elf, const char *name)
{
struct symbol *sym;

- elf_hash_for_each_possible(elf->symbol_name_hash, sym, name_hash, str_hash(name))
+ for_each_possible_sym(elf, name, sym)
if (!strcmp(sym->name, name))
return sym;

@@ -432,6 +435,8 @@ static int read_symbols(struct elf *elf)
list_for_each_entry(sym, &sec->symbol_list, list) {
char pname[MAX_NAME_LEN + 1];
size_t pnamelen;
+ struct symbol *psym;
+
if (sym->type != STT_FUNC)
continue;

@@ -454,8 +459,14 @@ static int read_symbols(struct elf *elf)

strncpy(pname, sym->name, pnamelen);
pname[pnamelen] = '\0';
- pfunc = find_symbol_by_name(elf, pname);
-
+ pfunc = NULL;
+ for_each_possible_sym(elf, pname, psym) {
+ if ((!psym->cfunc || psym->cfunc == psym) &&
+ !strcmp(psym->name, pname)) {
+ pfunc = psym;
+ break;
+ }
+ }
if (!pfunc) {
WARN("%s(): can't find parent function",
sym->name);