Re: [PATCH v3 1/3] tools/nolibc: unistd: Add getcwd()

[Willy Tarreau <w@1wt.eu>]

Hi Daniel,

On Thu, Jul 02, 2026 at 05:50:59PM +0900, Daniel Palmer wrote:
> Add getcwd() for getting the current working directory.
> 
> The behaviour matches what musl is doing except for one
> important difference: If the passed buf is NULL musl (and glibc)
> uses a big buffer on the stack and that is then strdup()'d and
> returned.
> 
> According to the man page for getcwd() this is a glibc extension
> and I don't think we need it in nolibc.

I entirely agree.

> Signed-off-by: Daniel Palmer <daniel@thingy.jp>
>
> ---
>  tools/include/nolibc/unistd.h | 42 +++++++++++++++++++++++++++++++++++
>  1 file changed, 42 insertions(+)
> 
> diff --git a/tools/include/nolibc/unistd.h b/tools/include/nolibc/unistd.h
> index 79599ceef45d..2e0edbc26315 100644
> --- a/tools/include/nolibc/unistd.h
> +++ b/tools/include/nolibc/unistd.h
> @@ -73,6 +73,48 @@ int ftruncate(int fd, off_t length)
>  	return __sysret(_sys_ftruncate(fd, length));
>  }
>  
> +/*
> + * char *getcwd(char *buf, size_t size);
> + */
> +
> +static __attribute__((unused))
> +int _sys_getcwd(char *buf, size_t size)
> +{
> +	return __nolibc_syscall2(__NR_getcwd, buf, size);
> +}
> +
> +static __attribute__((unused))
> +char *getcwd(char *buf, size_t size)
> +{
> +	int ret;
> +
> +	/* Unlike other libc's we don't handle passing NULL for buf */
> +	if (!buf || !size) {
> +		SET_ERRNO(EINVAL);
> +		return NULL;
> +	}
> +
> +	ret = __sysret(_sys_getcwd(buf, size));
> +
> +	/* On error return NULL, __sysret() above will have set errno */
> +	if (ret < 0)
> +		return NULL;
> +
> +	/* Handle no path being written or the kernel putting
> +	 * "(unreachable)" into the buffer instead of a path.
> +	 * This matches what musl is doing.
> +	 */
> +	if (ret == 0 || buf[0] != '/') {
> +		SET_ERRNO(ENOENT);
> +		return NULL;
> +	}
> +
> +	/* ret must be the number of bytes written at this point,
> +	 * so return the pointer to buf.
> +	 */
> +	return buf;
> +}
> +
>  static __attribute__((unused))
>  int msleep(unsigned int msecs)
>  {

LGTM. 

Acked-by: Willy Tarreau <w@1wt.eu>

Willy