On Sun, Sep 21, 2025 at 06:37:30PM +0200, Thomas Weißschuh wrote:
On 2025-09-21 09:55:11+0200, Willy Tarreau wrote:
Hi Benjamin,
On Fri, Sep 19, 2025 at 05:34:12PM +0200, Benjamin Berg wrote:
From: Benjamin Berg benjamin.berg@intel.com
There is no errno variable when NOLIBC_IGNORE_ERRNO is defined. As such, the perror function does not make any sense then and cannot compile.
Fixes: acab7bcdb1bc ("tools/nolibc/stdio: add perror() to report the errno value") Signed-off-by: Benjamin Berg benjamin.berg@intel.com Acked-by: Thomas Weißschuh linux@weissschuh.net
tools/include/nolibc/stdio.h | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h index 7630234408c5..c512159b8374 100644 --- a/tools/include/nolibc/stdio.h +++ b/tools/include/nolibc/stdio.h @@ -597,11 +597,13 @@ int sscanf(const char *str, const char *format, ...) return ret; } +#ifndef NOLIBC_IGNORE_ERRNO static __attribute__((unused)) void perror(const char *msg) { fprintf(stderr, "%s%serrno=%d\n", (msg && *msg) ? msg : "", (msg && *msg) ? ": " : "", errno); } +#endif
Please instead place the ifndef inside the function so that code calling perror() continues to build. The original goal of that macro was to further shrink programs at the expense of losing error details. But we should be able to continue to build working programs with that macro defined. There's nothing hard set in stone regarding this but here it's easy to preserve a working behavior by having something like this for example:
static __attribute__((unused)) void perror(const char *msg) { +#ifdef NOLIBC_IGNORE_ERRNO
- fprintf(stderr, "%s\n", (msg && *msg) ? msg : "unknown error");
+#else fprintf(stderr, "%s%serrno=%d\n", (msg && *msg) ? msg : "", (msg && *msg) ? ": " : "", errno); +#endif }
For the plain `errno` variable and printf(%m) we don't have such fallbacks. With NOLIBC_IGNORE_ERRNO the compilation either fails or the results are undefined. Personally I prefer not defining perror() here.
For me it's still a problem because that breaks the original purpose and current behavior. You cannot anymore compare the size of with/without errno for example, like here:
text data bss dec hex filename 20659 24 39424 60107 eacb init 19836 24 39424 59284 e794 init-noerrno
Perror doesn't just display the error name/number, it also prints a message about that error that doesn't need errno.
For "%m", that's fair enough, I didn't notice that one. We could imagine improving it by just emitting "?" or any such thing. But right now it will indeed proceed like you describe (that's already the case, it's not changed by this patch).
I don't want to block that patch but I'm annoyed that it unfairly blocks a legitimate error function that normally provides sufficient context in error paths so that errno can be ignored, such as here:
if (open(path, O_RDONLY) < 0) { perror("open()"); return -1; }
What's even more problematic is that Benjamin precisely fixed two other breakage cases in the same series for the same reason that they were blocking the build without errno, so it would be more consistent that this one isn't newly broken.
Willy