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libc: newlib: libc-hooks: Warn that there's no write() without POSIX_API #25479

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libc: newlib: libc-hooks: Warn that there's no write() without POSIX_API #25479

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16 changes: 15 additions & 1 deletion lib/libc/newlib/libc-hooks.c
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Original file line number Diff line number Diff line change
Expand Up @@ -182,7 +182,21 @@ __weak FUNC_ALIAS(_read, read, int);

int _write(int fd, const void *buf, int nbytes)
{
ARG_UNUSED(fd);
static const char msg[] = "Warning: write() called with fd!=STDOUT/ERR"
", consider enabling CONFIG_POSIX_API\n";

/* As we alias write() to _write() below, unsuspecting users may call
* it e.g. on a socket. This won't work, it requires CONFIG_POSIX_API
* to work properly. And the reason we define write() (by aliasing it)
* in the first place, is because some (prebuilt) Newlib variants
* for some architectures call into it (while other, well-behaving
* Newlib builds for other architectures, call into _write(), as
* expected and desired). Until that's fixed (on Newlib/Zephyr SDK
* side), warn unsuspecting users of the issue.
*/
if (fd != 1 && fd != 2) {
z_impl_zephyr_write_stdout(msg, sizeof(msg) - 1);
}

return z_impl_zephyr_write_stdout(buf, nbytes);
}
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