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

[Peter Zijlstra <peterz@infradead.org>]

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;