Re: [PATCH v3 06/21] perf dwarf-regs: Adapt get_dwarf_regnum() for arm64

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
- [Medium] The zero registers ('wzr' and 'xzr') are incorrectly mapped to DWARF register 31.
- [Medium] The link register ('lr') alias is no longer recognized and will unexpectedly return -ENOENT.
- [Low] The functions strcmp and strtol are used without explicitly including <string.h> and <stdlib.h>.
--

commit cf10eca9678152514cc1354dc6997be3eec9f436
Author: Tengda Wu <wutengda@huaweicloud.com>

perf dwarf-regs: Adapt get_dwarf_regnum() for arm64

This commit replaces the static string table lookup for arm64 DWARF registers
with a programmatic implementation in __get_dwarf_regnum_arm64(). This allows
resolving register names directly into their corresponding DWARF numbers
during annotation.

> 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 593ca7d4fccca..be55fc2a4f385 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 +1,6 @@
>  // SPDX-License-Identifier: GPL-2.0
>  #include <errno.h>
> +#include <ctype.h>

[Severity: Low]
Does omitting the explicit includes for <string.h> and <stdlib.h> break the
build on musl libc? 

This file now uses strcmp() and strtol() below, and musl strictly separates
declarations without relying on implicit inclusions.

>  #include <dwarf-regs.h>
>  #include "../../../arch/arm64/include/uapi/asm/perf_regs.h"

[ ... ]

> +int __get_dwarf_regnum_arm64(const char *name)
> +{
> +	int reg;
> +
> +	if (!strcmp(name, "sp") || !strcmp(name, "wzr") || !strcmp(name, "xzr"))
> +		return 31;

[Severity: Medium]
Does this incorrectly map the zero registers (wzr and xzr) to DWARF
register 31?

The AArch64 DWARF ABI assigns register 31 strictly to the stack pointer (sp),
and zero registers have no valid DWARF mapping.

Mapping wzr and xzr to 31 might cause perf annotate to conflate operations on
the zero register with stack pointer operations, leading to incorrect stack
variable tracking and type profiling statistics.

> +
> +	if (*name != 'x' && *name != 'w')
> +		return -ENOENT;

[Severity: Medium]
Will this strict prefix check reject the link register alias lr?

The previous static table lookup correctly mapped lr to register 30.
Because lr does not start with x or w, it appears this will now return
-ENOENT, which might break data type tracking for instructions that operate
on the link register.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260701035355.752944-1-wutengda@huaweicloud.com?part=6