Use strlcpy with >=glibc-2.38

Question

Use strlcpy with >=glibc-2.38

thesamesam opened this issue a year ago · 9 comments

glibc-2.38 includes strlcpy (and strlcat), musl has both for quite some time as well, but Makefile.linux currently unconditionally builds missing/strlcpy.c on Linux.

Please consider detecting a system implementation of strlcpy and using that if available.

Answer 1 · 2023-08-01T12:44:47.000Z

It appears that RedHat submitted this change but after the EL 9 release! This is a shame because it means that RedHat based systems won't get this feature for another 3-4 years.

Thanks for pointing this out, I will wait to see how other projects handle this.

Answer 2 · 2024-01-18T15:02:11.000Z

Reopening. strlcpy(3) is becoming more widely available (Fedora 39 for example). I'll investigate the best way to detect the system implementation.

Answer 3 · 2024-01-18T15:06:46.000Z

It appears that the _DEFAULT_SOURCE macro was defined for using BSD/misc functions

https://sourceware.org/git/?p=glibc.git;a=commit;h=c688b4196014e0162a1ff11120f6c9516be0c6cb

Answer 4 · 2024-01-18T17:45:36.000Z

Implemented in commit 1d7e1f3

Answer 5 · 2024-01-18T17:49:24.000Z

musl still needs _GNU_SOURCE or _BSD_SOURCE for it for now (until it's in a POSIX release officially), so I'd just use _GNU_SOURCE still for now?

Answer 6 · 2024-01-18T18:15:24.000Z

@thesamesam thanks for tip! I'll add _GNU_SOURCE back to the build

Answer 7 · 2024-01-18T18:24:16.000Z

Alpine Linux 3.19.0 does not seem to need _GNU_SOURCE. Is there something Alpine does differently to enable this feature in musl?

alpine:~/git/entr$ ldd entr
        /lib/ld-musl-x86_64.so.1 (0x7fc6356bb000)
        libc.musl-x86_64.so.1 => /lib/ld-musl-x86_64.so.1 (0x7fc6356bb000)

Answer 8 · 2024-01-18T19:01:48.000Z

I think gcc and clang default to -std=gnu11 (or gnu17) which implicitly enables _GNU_SOURCE.

If you try with make CFLAGS="-std=c99" or similar, you should get a failure. Adding _GNU_SOURCE fixes that.

For me, Clang does this on musl:

# printf '#include <string.h>\r\nint main() {}' | clang-x c -E - -O2 -dM | grep -i _SOURCE
#define _BSD_SOURCE 1
#define _XOPEN_SOURCE 700

musl's features.h does:

#if defined(_ALL_SOURCE) && !defined(_GNU_SOURCE)
#define _GNU_SOURCE 1
#endif

#if defined(_DEFAULT_SOURCE) && !defined(_BSD_SOURCE)
#define _BSD_SOURCE 1
#endif

#if !defined(_POSIX_SOURCE) && !defined(_POSIX_C_SOURCE) \
 && !defined(_XOPEN_SOURCE) && !defined(_GNU_SOURCE) \
 && !defined(_BSD_SOURCE) && !defined(__STRICT_ANSI__)
#define _BSD_SOURCE 1
#define _XOPEN_SOURCE 700
#endif

So, if nothing is defined, it does _BSD_SOURCE and _XOPEN_SOURCE 700 by default. Maybe we're fine then :)

(It's probably better to explicitly state what we want though with _GNU_SOURCE as that covers both musl and glibc and any -std= value the compiler might default to.)

Answer 9 · 2024-01-18T20:41:02.000Z

Ah exactly right.

In this case I also want to add -D_GNU_SOURCE to the configure script. Also should probably use cc as the compiler