linux-kernel - Re: [PATCH 01/16] perf: Unified API to record selective sets of arch registers

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Message-ID: <CABPqkBTshaU6cMnrcbO9aQ5GyO4rbNSSSP6_3DCD0YSZgS7tXA@mail.gmail.com>
Date:	Thu, 24 May 2012 14:13:19 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Jiri Olsa <jolsa@...hat.com>, acme@...hat.com, mingo@...e.hu,
	paulus@...ba.org, cjashfor@...ux.vnet.ibm.com, fweisbec@...il.com,
	gorcunov@...nvz.org, tzanussi@...il.com, mhiramat@...hat.com,
	robert.richter@....com, fche@...hat.com,
	linux-kernel@...r.kernel.org, masami.hiramatsu.pt@...achi.com,
	drepper@...il.com, asharma@...com, benjamin.redelings@...cent.org
Subject: Re: [PATCH 01/16] perf: Unified API to record selective sets of arch registers

2012/5/24 Peter Zijlstra <a.p.zijlstra@...llo.nl>:
> On Wed, 2012-05-23 at 21:32 +0200, Jiri Olsa wrote:
>> +enum perf_event_x86_32_regs {
>> +       PERF_X86_32_REG_EAX,
>> +       PERF_X86_32_REG_EBX,
>> +       PERF_X86_32_REG_ECX,
>> +       PERF_X86_32_REG_EDX,
>> +       PERF_X86_32_REG_ESI,
>> +       PERF_X86_32_REG_EDI,
>> +       PERF_X86_32_REG_EBP,
>> +       PERF_X86_32_REG_ESP,
>> +       PERF_X86_32_REG_EIP,
>> +       PERF_X86_32_REG_FLAGS,
>> +       PERF_X86_32_REG_CS,
>> +       PERF_X86_32_REG_DS,
>> +       PERF_X86_32_REG_ES,
>> +       PERF_X86_32_REG_FS,
>> +       PERF_X86_32_REG_GS,
>> +
>> +       /* Non ABI */
>> +       PERF_X86_32_REG_MAX,
>> +};
>
>> +enum perf_event_x86_64_regs {
>> +       PERF_X86_64_REG_RAX,
>> +       PERF_X86_64_REG_RBX,
>> +       PERF_X86_64_REG_RCX,
>> +       PERF_X86_64_REG_RDX,
>> +       PERF_X86_64_REG_RSI,
>> +       PERF_X86_64_REG_RDI,
>> +       PERF_X86_64_REG_R8,
>> +       PERF_X86_64_REG_R9,
>> +       PERF_X86_64_REG_R10,
>> +       PERF_X86_64_REG_R11,
>> +       PERF_X86_64_REG_R12,
>> +       PERF_X86_64_REG_R13,
>> +       PERF_X86_64_REG_R14,
>> +       PERF_X86_64_REG_R15,
>> +       PERF_X86_64_REG_RBP,
>> +       PERF_X86_64_REG_RSP,
>> +       PERF_X86_64_REG_RIP,
>> +       PERF_X86_64_REG_FLAGS,
>> +       PERF_X86_64_REG_CS,
>> +       PERF_X86_64_REG_SS,
>> +
>> +       /* Non ABI */
>> +       PERF_X86_64_REG_MAX,
>> +};
>
> So why bother with two different APIs? Why not have only the x86_64 one
> and maybe add a warning/error/fail whatever when x86_64 regs are
> selected on i386/compat tasks.
>
>
I agree with Peter here especially after our earlier discussion about how
to handle 32-bit ABI threads on a 64-bit ABI kernel. You should simply
fill in the record with zeroes when the register does not exists. You cannot
predict what will be sampled in system-wide mode.

The only sanity check you can do is on 32-bit ABI kernel, reject any 64-bit
ABI only regs but then that would require invoking arch specific code from
perf_copy_attr()....
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