Re: [PATCH v4 2/6] perf dwarf-aux: Fix libdw API contract violations

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The fix for uninitialized stack variables in `die_walk_lines` unconditionally filters out inline functions that lack a declaration line, breaking line walking for such functions.
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commit d271d4f48f3254386be3ea2c703448a90d59f608
Author: Ian Rogers <irogers@google.com>

perf dwarf-aux: Fix libdw API contract violations

This commit adds return value checks for several libdw API functions like
dwarf_decl_line(), dwarf_getfuncs(), and dwarf_lineaddr() to prevent using
uninitialized stack variables. It gracefully handles optional dwarf_decl_line()
calls for the root DIE, adds NULL pointer protection for strcmp(), and uses
dwarf_attr_integrate() for member locations.

> diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
> index 109a166a6d19..a8ab1c30d0ac 100644
> --- a/tools/perf/util/dwarf-aux.c
> +++ b/tools/perf/util/dwarf-aux.c

[ ... ]

> @@ -998,12 +993,11 @@ int die_walk_lines(Dwarf_Die *rt_die, line_walk_callback_t callback, void *data)
>  			if (die_find_inlinefunc(rt_die, addr, &die_mem)) {
>  				/* Call-site check */
>  				inf = die_get_call_file(&die_mem);
> -				if ((inf && !strcmp(inf, decf)) &&
> +				if ((inf == decf || (inf && decf && !strcmp(inf, decf))) &&
>  				    die_get_call_lineno(&die_mem) == lineno)
>  					goto found;
>  
> -				dwarf_decl_line(&die_mem, &inl);
> -				if (inl != decl ||
> +				if (dwarf_decl_line(&die_mem, &inl) != 0 || inl != decl ||
>  				    decf != die_get_decl_file(&die_mem))
>  					continue;
>  			}

If the root function lacks a declaration line, could this strict check cause us
to skip valid matching lines from inline instances?

The commit message notes that dwarf_decl_line() is optional for the root DIE
and its failures are handled gracefully. This leaves decl = 0 if the
declaration line is missing.

However, if the root function lacks a declaration line, its inline instances
will also lack one. When dwarf_decl_line(&die_mem, &inl) fails here, it now
evaluates to non-zero and forcefully continues the loop.

Should inl be safely defaulted to 0 on failure here to match the graceful
handling of the root DIE, rather than aborting the match entirely?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260503171032.1559338-1-irogers@google.com?part=2