Re: [PATCH v5 07/26] perf dwarf-regs: Adapt get_dwarf_regnum() for arm64

[Tengda Wu]

On 2026/9/9 2:08, Ian Rogers wrote:
> On Tue, Sep 8, 2026 at 6:01 AM Tengda Wu <wutengda@xxxxxxxxxxxxxxx> wrote:
>>
>> The current arm64 DWARF register lookup relies on 'aarch64_regstr_tbl',
>> a static string table. While this works for kprobe-tracer where register
>> names start with '%', it is insufficient for parsing register numbers
>> directly from raw instructions (e.g., extracting '6' from 'x6' or 'w6')
>> during annotation.
>>
>> Since get_dwarf_regnum() is currently used only by 'perf annotate' and
>> does not affect kprobe-tracer, replace the limited table-based lookup
>> with a programmatic implementation in __get_dwarf_regnum_arm64(). This
>> allows resolving arm64 register names (x0-x30, w0-w30, sp, etc.) directly
>> into their corresponding DWARF register numbers.
>>
>> Signed-off-by: Tengda Wu <wutengda@xxxxxxxxxxxxxxx>
>> ---
>>  .../util/dwarf-regs-arch/dwarf-regs-arm64.c   | 22 +++++++++++++++++++
>>  tools/perf/util/dwarf-regs.c                  |  2 +-
>>  tools/perf/util/include/dwarf-regs.h          |  1 +
>>  3 files changed, 24 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/perf/util/dwarf-regs-arch/dwarf-regs-arm64.c b/tools/perf/util/dwarf-regs-arch/dwarf-regs-arm64.c
>> index 593ca7d4fccc..720c863d1869 100644
>> --- a/tools/perf/util/dwarf-regs-arch/dwarf-regs-arm64.c
>> +++ b/tools/perf/util/dwarf-regs-arch/dwarf-regs-arm64.c
>> @@ -1,5 +1,8 @@
>>  // SPDX-License-Identifier: GPL-2.0
>>  #include <errno.h>
>> +#include <ctype.h>
>> +#include <stdlib.h>
>> +#include <string.h>
>>  #include <dwarf-regs.h>
>>  #include "../../../arch/arm64/include/uapi/asm/perf_regs.h"
>>
>> @@ -10,3 +13,22 @@ int __get_dwarf_regnum_for_perf_regnum_arm64(int perf_regnum)
>>
>>         return perf_regnum;
>>  }
>> +
>> +int __get_dwarf_regnum_arm64(const char *name)
>> +{
>> +       int reg;
>> +
>> +       if (!strcmp(name, "sp"))
>> +               return 31;
>> +
>> +       if (*name != 'x' && *name != 'w')
>> +               return -ENOENT;
>> +
>> +       name++;
>> +       if (!isdigit(*name))
>> +               return -ENOENT;
>> +
>> +       reg = strtol(name, NULL, 10);
> 
> Nit: perhaps this can be a little faster and ensure correct string termination?
> ```
> if (!isdigit(name[0])) {
>     return -ENOENT;
> } else if (isdigit(name[1]) && name[2] == '\0') {
>      reg = (name[1] - ' 0') * 10 + name[2] - '0';
> } else if (name[1] == '\0) {
>    reg = name[1] - '0';
> } else {
>    return -ENOENT;
> }
> ```
> Everything else looks good to me.
> 
> Thanks,
> Ian
> 

Sure, Ian. Thanks for the review. I'll make the change in v6.

Thanks,
Tengda

>> +
>> +       reg = strtol(name, NULL, 10);
>> +
>> +       return reg >= 0 && reg <= 30 ? reg : -ENOENT;
>> +}
>> diff --git a/tools/perf/util/dwarf-regs.c b/tools/perf/util/dwarf-regs.c
>> index 797f455eba0d..bacf5c13c3bc 100644
>> --- a/tools/perf/util/dwarf-regs.c
>> +++ b/tools/perf/util/dwarf-regs.c
>> @@ -114,7 +114,7 @@ int get_dwarf_regnum(const char *name, unsigned int machine, unsigned int flags)
>>                 reg = _get_dwarf_regnum(arm_regstr_tbl, name);
>>                 break;
>>         case EM_AARCH64:
>> -               reg = _get_dwarf_regnum(aarch64_regstr_tbl, name);
>> +               reg = __get_dwarf_regnum_arm64(name);
>>                 break;
>>         case EM_CSKY:
>>                 reg = __get_csky_regnum(name, flags);
>> diff --git a/tools/perf/util/include/dwarf-regs.h b/tools/perf/util/include/dwarf-regs.h
>> index 46a764cf322f..a25f038bbff2 100644
>> --- a/tools/perf/util/include/dwarf-regs.h
>> +++ b/tools/perf/util/include/dwarf-regs.h
>> @@ -105,6 +105,7 @@ int __get_dwarf_regnum_x86_64(const char *name);
>>  int __get_dwarf_regnum_for_perf_regnum_i386(int perf_regnum);
>>  int __get_dwarf_regnum_for_perf_regnum_x86_64(int perf_regnum);
>>
>> +int __get_dwarf_regnum_arm64(const char *name);
>>  int __get_dwarf_regnum_for_perf_regnum_arm(int perf_regnum);
>>  int __get_dwarf_regnum_for_perf_regnum_arm64(int perf_regnum);
>>
>> --
>> 2.34.1
>>