Re: [PATCH 0/8] unwind, arm64: add sframe unwinder for kernel

Song Liu
2025-02-25T00:14:10Z

On Thu, Feb 20, 2025 at 10:33 AM Song Liu <song@kernel.org> wrote:
>
>
> On Thu, Feb 20, 2025 at 10:22 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>>
>> On Wed, Feb 19, 2025 at 08:50:09PM -0800, Song Liu wrote:
>> > Indu, is this behavior (symbols with same name are not in
>> > sorted order from readelf -s) expected? Or is this a bug?
>> > I am using this gcc:
>> >
>> > $ gcc --version
>> > gcc (GCC) 14.2.1 20240801 (Red Hat 14.2.1-1)
>> > Copyright (C) 2024 Free Software Foundation, Inc.
>> > This is free software; see the source for copying conditions. There is NO
>> > warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
>>
>> Are you using different binutils versions as well?
>
>
> I am using binutil 2.41, for both gcc -11 and gcc-14.
>
>>
>> It sounds like a linker "issue" to me. I'm not sure if it qualifies as
>> a bug, the linker might be free to layout symbols how it wishes.
>
>
> We can probably handle that in kpatch-build.

OK, something like the following gets the proper sympos for
gcc-14 built kernel.

Thanks,
Song

diff --git i/kpatch-build/lookup.c w/kpatch-build/lookup.c
index bd2b732de910..87ac127184c5 100644
--- i/kpatch-build/lookup.c
+++ w/kpatch-build/lookup.c
@@ -479,13 +479,10 @@ static bool lookup_local_symbol(struct
lookup_table *table,
struct object_symbol *sym;
unsigned long sympos = 0;
int i, in_file = 0;
+ bool found = false;

memset(result, 0, sizeof(*result));
for_each_obj_symbol(i, sym, table) {
- if (sym->bind == STB_LOCAL && !strcmp(sym->name,
- lookup_sym->name))
- sympos++;
-
if (lookup_sym->lookup_table_file_sym == sym) {
in_file = 1;
continue;
@@ -499,20 +496,29 @@ static bool lookup_local_symbol(struct
lookup_table *table,

if (sym->bind == STB_LOCAL && !strcmp(sym->name,
lookup_sym->name)) {
- if (result->objname)
+ if (found)
ERROR("duplicate local symbol found for %s",
lookup_sym->name);

result->objname = table->objname;
result->addr = sym->addr;
result->size = sym->size;
- result->sympos = sympos;
result->global = false;
result->exported = false;
+ found = true;
}
}
+ if (!found)
+ return false;

- return !!result->objname;
+ for_each_obj_symbol(i, sym, table) {
+ if (sym->bind == STB_LOCAL &&
+ !strcmp(sym->name, lookup_sym->name) &&
+ sym->addr < result->addr)
+ sympos++;
+ }
+ result->sympos = sympos;
+ return true;
}

static bool lookup_exported_symbol(struct lookup_table *table, char *name,