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

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Date:   Tue, 24 May 2022 16:30:13 +0530
From:   Sathvika Vasireddy <sv@...ux.vnet.ibm.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mbenes@...e.cz" <mbenes@...e.cz>, "aik@...abs.ru" <aik@...abs.ru>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "naveen.n.rao@...ux.vnet.ibm.com" <naveen.n.rao@...ux.vnet.ibm.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Sathvika Vasireddy <sv@...ux.ibm.com>
Subject: Re: [RFC PATCH 4/4] objtool/powerpc: Add --mcount specific
 implementation


On 24/05/22 15:05, Christophe Leroy wrote:
>
> 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@...ux.ibm.com>
>> ---
>>    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.
Makes sense. I'll make this a separate patch in the next revision.
>
>>    
>>    	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'.
Sure, I'll rename it to elf_reloc_type() or some such.
>
>> +{
>> +	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 ?

This is so that we can support cross architecture builds.


Thanks for reviewing!

- Sathvika