Re: [PATCH 4/4] perf symbol: Add missing libgen.h include to get basename() prototype

[Ian Rogers]

On Wed, Apr 1, 2026 at 5:20 PM Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:
>
> From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
>
> This works in some places because there are tricks to prefer a GNU
> version instead of the XPG version, but started breaking in some musl
> libc systems due to some unrelated change that made libgen.h stop being
> included by chance.
>
> Since symbol.h is using basename(), make it include libgen.h.

Huh, this is being flagged by Sashiko:
"""
Could this include cause segmentation faults by exposing the POSIX version
of basename() to the rest of the tools?

According to the POSIX specification, if the input is an empty string
or slashes, basename() can return a pointer to a statically allocated,
read-only string literal (such as "." or "/").

In tools/perf/util/probe-event.c:convert_exec_to_group(), the code takes
the return value of basename() and modifies it in-place:
    ptr = basename(exec);
    ...
    for (ptr2 = ptr; *ptr2 != '\0'; ptr2++) {
            if (!isalnum(*ptr2) && *ptr2 != '_')
                    *ptr2 = '_';
    }
If a user provides an empty target or "/", the POSIX basename() would
return a read-only string. When the loop attempts to write a null or
underscore into it, wouldn't it trigger an immediate segmentation fault?

Is there a way we can safely duplicate the returned string before modifying it,
or ensure the inputs never resolve to these static strings?
"""

The story of the two basename versions and the issues appears in the
man pages. The whole thing makes me think we should avoid basename :-)

Thanks,
Ian

> Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> ---
>  tools/perf/util/symbol.h | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
> index c67814d6d6d6f64a..b37ecc2e90f77efe 100644
> --- a/tools/perf/util/symbol.h
> +++ b/tools/perf/util/symbol.h
> @@ -10,6 +10,7 @@
>  #include <linux/rbtree.h>
>  #include <stdio.h>
>  #include <errno.h>
> +#include <libgen.h>
>  #include "addr_location.h"
>  #include "path.h"
>  #include "symbol_conf.h"
> --
> 2.53.0
>