linux-kernel - Re: [PATCH v4 05/10] objtool: Handle unreachable entry of rodata

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Message-ID: <20537f77-e105-317b-7f95-8a72533c8e43@loongson.cn>
Date: Tue, 26 Nov 2024 19:04:39 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Huacai Chen <chenhuacai@...nel.org>, Peter Zijlstra
 <peterz@...radead.org>, loongarch@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 05/10] objtool: Handle unreachable entry of rodata

On 11/26/2024 03:25 PM, Josh Poimboeuf wrote:
> On Fri, Nov 22, 2024 at 12:50:00PM +0800, Tiezhu Yang wrote:
>> When compling with Clang on LoongArch, there exists unreachable entry of
>> rodata which points to a position after the function return instruction,
>> this is generated by compiler to fill the non-existent switch case, just
>> skip the entry when parsing the relocation section of rodata.
>>
>> This is preparation for later patch on LoongArch, there is no effect for
>> the other archs with this patch.
>>
>> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
>> ---
>>  tools/objtool/check.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
>> index 8733ca620cca..b21e47d8d3d1 100644
>> --- a/tools/objtool/check.c
>> +++ b/tools/objtool/check.c
>> @@ -2144,6 +2144,13 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
>>  		if (!dest_insn)
>>  			break;
>>
>> +		/* Handle the special cases compiled with Clang on LoongArch */
>> +		if (file->elf->ehdr.e_machine == EM_LOONGARCH && reloc->sym->type == STT_SECTION &&
>> +		    (!insn_func(dest_insn) || insn_func(dest_insn)->pfunc != pfunc)) {
>> +			prev_offset = reloc_offset(reloc);
>> +			continue;
>
> Are you sure this is specific to loongarch?

I am not sure, I only found this issue on LoongArch compiled with Clang,
but I think there is no effect if make it generic, like this:

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index f7586f82b967..87302e6fc07f 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2103,9 +2103,10 @@ static int add_jump_table(struct objtool_file 
*file, struct instruction *insn,
                 if (!dest_insn)
                         break;

-               /* Make sure the destination is in the same function: */
-               if (!insn_func(dest_insn) || insn_func(dest_insn)->pfunc 
!= pfunc)
-                       break;
+               if (!insn_func(dest_insn) || insn_func(dest_insn)->pfunc 
!= pfunc) {
+                       prev_offset = reloc_offset(reloc);
+                       continue;
+               }

                 alt = malloc(sizeof(*alt));
                 if (!alt) {

If you are OK, I will modify it.

Thanks,
Tiezhu