Re: [RFC PATCH 4/4] objtool/powerpc: Add --mcount specific implementation

[Christophe Leroy]

Le 23/05/2022 à 19:55, Sathvika Vasireddy a écrit :
> This patch enables objtool --mcount on powerpc, and
> adds implementation specific to powerpc.
> 
> Signed-off-by: Sathvika Vasireddy <sv@xxxxxxxxxxxxx>
> ---
>   arch/powerpc/Kconfig                |  1 +
>   tools/objtool/arch/powerpc/decode.c | 14 ++++++++++++++
>   tools/objtool/check.c               | 12 +++++++-----
>   tools/objtool/elf.c                 | 13 +++++++++++++
>   tools/objtool/include/objtool/elf.h |  1 +
>   5 files changed, 36 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 732a3f91ee5e..3373d44a1298 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -233,6 +233,7 @@ config PPC
>   	select HAVE_NMI				if PERF_EVENTS || (PPC64 && PPC_BOOK3S)
>   	select HAVE_OPTPROBES
>   	select HAVE_OBJTOOL			if PPC64
> +	select HAVE_OBJTOOL_MCOUNT		if HAVE_OBJTOOL
>   	select HAVE_PERF_EVENTS
>   	select HAVE_PERF_EVENTS_NMI		if PPC64
>   	select HAVE_PERF_REGS
> diff --git a/tools/objtool/arch/powerpc/decode.c b/tools/objtool/arch/powerpc/decode.c
> index e3b77a6ce357..ad3d79fffac2 100644
> --- a/tools/objtool/arch/powerpc/decode.c
> +++ b/tools/objtool/arch/powerpc/decode.c
> @@ -40,12 +40,26 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
>   			    struct list_head *ops_list)
>   {
>   	u32 insn;
> +	unsigned int opcode;
>   
>   	*immediate = 0;
>   	memcpy(&insn, sec->data->d_buf+offset, 4);
>   	*len = 4;
>   	*type = INSN_OTHER;
>   
> +	opcode = (insn >> 26);

You dont need the brackets here.

> +
> +	switch (opcode) {
> +	case 18: /* bl */
> +		if ((insn & 3) == 1) {
> +			*type = INSN_CALL;
> +			*immediate = insn & 0x3fffffc;
> +			if (*immediate & 0x2000000)
> +				*immediate -= 0x4000000;
> +		}
> +		break;
> +	}
> +
>   	return 0;
>   }
>   
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index 056302d58e23..fd8bad092f89 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -832,7 +832,7 @@ static int create_mcount_loc_sections(struct objtool_file *file)
>   
>   		if (elf_add_reloc_to_insn(file->elf, sec,
>   					  idx * sizeof(unsigned long),
> -					  R_X86_64_64,
> +					  elf_reloc_type_long(file->elf),
>   					  insn->sec, insn->offset))
>   			return -1;
>   
> @@ -2183,7 +2183,7 @@ static int classify_symbols(struct objtool_file *file)
>   			if (arch_is_retpoline(func))
>   				func->retpoline_thunk = true;
>   
> -			if (!strcmp(func->name, "__fentry__"))
> +			if ((!strcmp(func->name, "__fentry__")) || (!strcmp(func->name, "_mcount")))
>   				func->fentry = true;
>   
>   			if (is_profiling_func(func->name))
> @@ -2259,9 +2259,11 @@ static int decode_sections(struct objtool_file *file)
>   	 * Must be before add_jump_destinations(), which depends on 'func'
>   	 * being set for alternatives, to enable proper sibling call detection.
>   	 */
> -	ret = add_special_section_alts(file);
> -	if (ret)
> -		return ret;
> +	if (opts.stackval || opts.orc || opts.uaccess || opts.noinstr) {
> +		ret = add_special_section_alts(file);
> +		if (ret)
> +			return ret;
> +	}

I think this change should be a patch by itself, it's not related to 
powerpc.

>   
>   	ret = add_jump_destinations(file);
>   	if (ret)
> diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
> index c25e957c1e52..95763060d551 100644
> --- a/tools/objtool/elf.c
> +++ b/tools/objtool/elf.c
> @@ -793,6 +793,19 @@ elf_create_section_symbol(struct elf *elf, struct section *sec)
>   	return sym;
>   }
>   
> +int elf_reloc_type_long(struct elf *elf)

Not sure it's a good name, because for 32 bits we have to use 'int'.

> +{
> +	switch (elf->ehdr.e_machine) {
> +	case EM_X86_64:
> +		return R_X86_64_64;
> +	case EM_PPC64:
> +		return R_PPC64_ADDR64;
> +	default:
> +		WARN("unknown machine...");
> +		exit(-1);
> +	}
> +}

Wouldn't it be better to make that function arch specific ?

> +
>   int elf_add_reloc_to_insn(struct elf *elf, struct section *sec,
>   			  unsigned long offset, unsigned int type,
>   			  struct section *insn_sec, unsigned long insn_off)
> diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
> index adebfbc2b518..c43e23c0b3c8 100644
> --- a/tools/objtool/include/objtool/elf.h
> +++ b/tools/objtool/include/objtool/elf.h
> @@ -144,6 +144,7 @@ static inline bool has_multiple_files(struct elf *elf)
>   struct elf *elf_open_read(const char *name, int flags);
>   struct section *elf_create_section(struct elf *elf, const char *name, unsigned int sh_flags, size_t entsize, int nr);
>   
> +int elf_reloc_type_long(struct elf *elf);
>   int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset,
>   		  unsigned int type, struct symbol *sym, s64 addend);
>   int elf_add_reloc_to_insn(struct elf *elf, struct section *sec,