Re: [RFC PATCH 3/3] objtool/mcount: Add powerpc specific functions

[Peter Zijlstra]

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;