linux-kernel - Re: [RFC PATCH v3 07/12] objtool: Use macros to define arch specific reloc types

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Message-ID: <47f7a3db-7b34-1991-11df-f0f7e1317614@csgroup.eu>
Date:   Mon, 4 Jul 2022 15:53:50 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Peter Zijlstra <peterz@...radead.org>,
        Sathvika Vasireddy <sv@...ux.ibm.com>,
        "g@...ez.programming.kicks-ass.net" 
        <g@...ez.programming.kicks-ass.net>
CC:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "aik@...abs.ru" <aik@...abs.ru>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "naveen.n.rao@...ux.vnet.ibm.com" <naveen.n.rao@...ux.vnet.ibm.com>,
        "mbenes@...e.cz" <mbenes@...e.cz>,
        "benh@...nel.crashing.org" <benh@...nel.crashing.org>,
        "paulus@...ba.org" <paulus@...ba.org>
Subject: Re: [RFC PATCH v3 07/12] objtool: Use macros to define arch specific
 reloc types



Le 04/07/2022 à 13:14, Peter Zijlstra a écrit :
> On Sat, Jun 25, 2022 at 12:02:33AM +0530, Sathvika Vasireddy wrote:
>> Make relocation types architecture specific.
>>
>> Signed-off-by: Sathvika Vasireddy <sv@...ux.ibm.com>
>> ---
>>   tools/objtool/arch/x86/include/arch/elf.h | 2 ++
>>   tools/objtool/check.c                     | 2 +-
>>   2 files changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/objtool/arch/x86/include/arch/elf.h b/tools/objtool/arch/x86/include/arch/elf.h
>> index 69cc4264b28a..ac14987cf687 100644
>> --- a/tools/objtool/arch/x86/include/arch/elf.h
>> +++ b/tools/objtool/arch/x86/include/arch/elf.h
>> @@ -2,5 +2,7 @@
>>   #define _OBJTOOL_ARCH_ELF
>>   
>>   #define R_NONE R_X86_64_NONE
>> +#define R_ABS64 R_X86_64_64
>> +#define R_ABS32 R_X86_64_32
>>   
>>   #endif /* _OBJTOOL_ARCH_ELF */
>> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
>> index 98e869721bc4..88f68269860e 100644
>> --- a/tools/objtool/check.c
>> +++ b/tools/objtool/check.c
>> @@ -834,7 +834,7 @@ static int create_mcount_loc_sections(struct objtool_file *file)
>>   		memset(loc, 0, size);
>>   
>>   		if (elf_add_reloc_to_insn(file->elf, sec, idx,
>> -					  R_X86_64_64,
>> +					  size == sizeof(u64) ? R_ABS64 : R_ABS32,
>>   					  insn->sec, insn->offset))
>>   			return -1;
>>   
> 
> Given cross compiles, should this not also be elf dependent?

size is elf dependent (From the same series [RFC PATCH v3 03/12] 
objtool: Use target file class size instead of a compiled constant)

R_ABS64 and R_ABS32 are defined in the architecture elf.h, and this is 
the architecture for which you are building your kernel, not the 
architecture you cross compile on.