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

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Message-ID: <20120607094624.GB19842@somewhere.redhat.com>
Date:	Thu, 7 Jun 2012 11:46:29 +0200
From:	Frederic Weisbecker <fweisbec@...il.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, eranian@...gle.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

On Thu, May 24, 2012 at 11:43:56AM +0200, Peter Zijlstra wrote:
> On Wed, 2012-05-23 at 21:32 +0200, Jiri Olsa wrote:
> > +static inline u64 perf_reg_value(struct pt_regs *regs, int idx)
> > +{
> > +       switch (idx) {
> > +       case PERF_X86_32_REG_EAX:
> > +               return regs->ax;
> > +       case PERF_X86_32_REG_EBX:
> > +               return regs->bx;
> > +       case PERF_X86_32_REG_ECX:
> > +               return regs->cx;
> > +       case PERF_X86_32_REG_EDX:
> > +               return regs->dx;
> > +       case PERF_X86_32_REG_ESI:
> > +               return regs->si;
> > +       case PERF_X86_32_REG_EDI:
> > +               return regs->di;
> > +       case PERF_X86_32_REG_EBP:
> > +               return regs->bp;
> > +       case PERF_X86_32_REG_ESP:
> > +               return regs->sp;
> > +       case PERF_X86_32_REG_EIP:
> > +               return regs->ip;
> > +       case PERF_X86_32_REG_FLAGS:
> > +               return regs->flags;
> > +       case PERF_X86_32_REG_CS:
> > +               return regs->cs;
> > +       case PERF_X86_32_REG_DS:
> > +               return regs->ds;
> > +       case PERF_X86_32_REG_ES:
> > +               return regs->es;
> > +       case PERF_X86_32_REG_FS:
> > +               return regs->fs;
> > +       case PERF_X86_32_REG_GS:
> > +               return regs->gs;
> > +       }
> > +
> > +       return 0;
> > +} 
> 
> This is just sad... is there really no saner way to write this? I
> suppose you're going to iterate your sample_regs bitmap and call this
> function for every bit. GCC isn't known to generate particularly sane
> code for switches :/
> 

Do you think that compat regs are always a subset of native regs in all
archs as in x86? Sounds logic but I'm asking just in case. If so then yeah
this should work.
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