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Message-ID: <578ec055-0d63-e579-0caa-ad57846b8995@csgroup.eu>
Date: Tue, 24 May 2022 13:33:33 +0000
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Sathvika Vasireddy <sv@...ux.vnet.ibm.com>
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
Le 24/05/2022 à 13:00, Sathvika Vasireddy a écrit :
> [Vous ne recevez pas souvent de courriers de la part de
> sv@...ux.vnet.ibm.com. Découvrez pourquoi cela peut être important à
> l’adresse https://aka.ms/LearnAboutSenderIdentification.]
>
> 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.
Great. Can you base your next revision on the one I just sent out ?
I will now start looking at inline static calls for PPC32.
>>
>>>
>>> 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.
>
I'm not sure I follow you here.
This is only based on the target, it doesn't depend on the build host so
I can't the link with cross arch builds.
The same as you have arch_decode_instruction(), you could have
arch_elf_reloc_type_long()
It would make sense indeed, because there is no point in supporting X86
relocation when you don't support X86 instruction decoding.
Christophe
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