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SubjectRe: [RFC PATCH 3/3] objtool/mcount: Add powerpc specific functions
Peter Zijlstra wrote:
> On Fri, Mar 18, 2022 at 04:21:40PM +0530, Sathvika Vasireddy wrote:
>> This patch adds powerpc specific functions required for
>> 'objtool mcount' to work, and enables mcount for ppc.
>
> I would love to see more objtool enablement for Power :-)
>
>
>> diff --git a/tools/objtool/arch/powerpc/include/arch/elf.h b/tools/objtool/arch/powerpc/include/arch/elf.h
>> new file mode 100644
>> index 000000000000..3c8ebb7d2a6b
>> --- /dev/null
>> +++ b/tools/objtool/arch/powerpc/include/arch/elf.h
>> @@ -0,0 +1,8 @@
>> +/* SPDX-License-Identifier: GPL-2.0-or-later */
>> +
>> +#ifndef _OBJTOOL_ARCH_ELF
>> +#define _OBJTOOL_ARCH_ELF
>> +
>> +#define R_NONE R_PPC_NONE
>> +
>> +#endif /* _OBJTOOL_ARCH_ELF */
>> diff --git a/tools/objtool/utils.c b/tools/objtool/utils.c
>> index d1fc6a123a6e..c9c14fa0dfd7 100644
>> --- a/tools/objtool/utils.c
>> +++ b/tools/objtool/utils.c
>> @@ -179,11 +179,29 @@ int create_mcount_loc_sections(struct objtool_file *file)
>> loc = (unsigned long *)sec->data->d_buf + idx;
>> memset(loc, 0, sizeof(unsigned long));
>>
>> - if (elf_add_reloc_to_insn(file->elf, sec,
>> - idx * sizeof(unsigned long),
>> - R_X86_64_64,
>> - insn->sec, insn->offset))
>> - return -1;
>> + if (file->elf->ehdr.e_machine == EM_X86_64) {
>> + if (elf_add_reloc_to_insn(file->elf, sec,
>> + idx * sizeof(unsigned long),
>> + R_X86_64_64,
>> + insn->sec, insn->offset))
>> + return -1;
>> + }
>> +
>> + if (file->elf->ehdr.e_machine == EM_PPC64) {
>> + if (elf_add_reloc_to_insn(file->elf, sec,
>> + idx * sizeof(unsigned long),
>> + R_PPC64_ADDR64,
>> + insn->sec, insn->offset))
>> + return -1;
>> + }
>> +
>> + if (file->elf->ehdr.e_machine == EM_PPC) {
>> + if (elf_add_reloc_to_insn(file->elf, sec,
>> + idx * sizeof(unsigned long),
>> + R_PPC_ADDR32,
>> + insn->sec, insn->offset))
>> + return -1;
>> + }
>
> It appears to me that repeating this code 3 times doesn't really scale
> well, how about we introduce a helper like:
>
>
> int elf_reloc_type_long(struct elf *elf)
> {
> switch (elf->ehdr.e_machine) {
> case EM_X86_64:
> return R_X86_64_64;
> case EM_PPC64:
> return R_PPC64_ADDR64;
> case EM_PPC:
> return R_PPC_ADDR32;
> default:
> WARN("unknown machine...")
> exit(-1);
> }
> }
>
> if (elf_add_reloc_to_insn(file->elf, sec,
> idx * sizeof(unsigned long),
> elf_reloc_type_long(file->elf),
> insn->sec, insn->offset))
> return -1;

Good point. I suppose we'll need a similar helper, say,
elf_reloc_type_none(), to replace R_NONE usage if we want to have
objtool work for cross-arch builds.


- Naveen

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