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

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Message-ID: <CAPhsuW5Codoe2NViZJRE4JjM2Qc_v-qPzKZ1vOyr+9Oi0CxpAQ@mail.gmail.com>
Date: Mon, 24 Feb 2025 16:13:58 -0800
From: Song Liu <song@...nel.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Puranjay Mohan <puranjay@...nel.org>, Weinan Liu <wnliu@...gle.com>, 
	Steven Rostedt <rostedt@...dmis.org>, Indu Bhagat <indu.bhagat@...cle.com>, 
	Peter Zijlstra <peterz@...radead.org>, Mark Rutland <mark.rutland@....com>, roman.gushchin@...ux.dev, 
	Will Deacon <will@...nel.org>, Ian Rogers <irogers@...gle.com>, linux-toolchains@...r.kernel.org, 
	linux-kernel@...r.kernel.org, live-patching@...r.kernel.org, 
	joe.lawrence@...hat.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 0/8] unwind, arm64: add sframe unwinder for kernel

On Thu, Feb 20, 2025 at 10:33 AM Song Liu <song@...nel.org> wrote:
>
>
> On Thu, Feb 20, 2025 at 10:22 AM Josh Poimboeuf <jpoimboe@...nel.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,