linux-kernel - Re: [PATCH V2 8/9] tools/perf: Add support to find global register variables using find_data_type_global

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Date: Fri, 24 May 2024 17:47:02 +0530
From: Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: "acme@...nel.org" <acme@...nel.org>, "jolsa@...nel.org" <jolsa@...nel.org>,
        "adrian.hunter@...el.com" <adrian.hunter@...el.com>,
        "irogers@...gle.com" <irogers@...gle.com>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "segher@...nel.crashing.org" <segher@...nel.crashing.org>,
        "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "maddy@...ux.ibm.com" <maddy@...ux.ibm.com>,
        "kjain@...ux.ibm.com" <kjain@...ux.ibm.com>,
        "disgoel@...ux.vnet.ibm.com" <disgoel@...ux.vnet.ibm.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "akanksha@...ux.ibm.com" <akanksha@...ux.ibm.com>
Subject: Re: [PATCH V2 8/9] tools/perf: Add support to find global register
 variables using find_data_type_global_reg



> On 7 May 2024, at 3:33 PM, Christophe Leroy <christophe.leroy@...roup.eu> wrote:
> 
> 
> 
> Le 06/05/2024 à 14:19, Athira Rajeev a écrit :
>> There are cases where define a global register variable and associate it
>> with a specified register. Example, in powerpc, two registers are
>> defined to represent variable:
>> 1. r13: represents local_paca
>> register struct paca_struct *local_paca asm("r13");
>> 
>> 2. r1: represents stack_pointer
>> register void *__stack_pointer asm("r1");
> 
> What about r2:
> 
> register struct task_struct *current asm ("r2");

Hi Christophe,

Referring to arch/powerpc/include/asm/current.h, “current” in powerpc 64 bit is from paca_struct which is handled with r13
R2 definition which you shared above is for 32 bit case.

Thanks
Athira
> 
>> 
>> These regs are present in dwarf debug as DW_OP_reg as part of variables
>> in the cu_die (compile unit). These are not present in die search done
>> in the list of nested scopes since these are global register variables.
>>