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

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Date:   Mon, 4 Jul 2022 18:18:32 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Sathvika Vasireddy <sv@...ux.ibm.com>,
        "g@...ez.programming.kicks-ass.net" 
        <g@...ez.programming.kicks-ass.net>,
        "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

On Mon, Jul 04, 2022 at 03:53:50PM +0000, Christophe Leroy wrote:
> 
> 
> 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.

Duh. Thanks!