Re: Some questions

[Rich Felker <dalias@libc.org>]

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On Mon, Apr 30, 2018 at 03:29:39PM +1000, Patrick Oppenlander wrote:
> On Mon, Apr 30, 2018 at 1:16 PM, Rich Felker <dalias@libc.org> wrote:
> > On Mon, Apr 30, 2018 at 12:52:06PM +1000, Patrick Oppenlander wrote:
> >> - getcwd returned buffer size can be incorrect. If you call
> >> getcwd(NULL, 1234) the returned buffer is sized to match the path
> >> length but should be 1234 to be compatible with the glibc extension.
> >
> > I'll look at this. It seems like a worse behavior for most callers,
> > but maybe it should match.
> 
> Actually, my biggest issue with getcwd is that it allocates a PATH_MAX
> sized buffer on the stack. That's painful on deeply embedded stuff.

That's unrelated, and could/should be fixed by the attached patch I
think.

Rich

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diff --git a/src/unistd/getcwd.c b/src/unistd/getcwd.c
index 103fbbb..f407ffe 100644
--- a/src/unistd/getcwd.c
+++ b/src/unistd/getcwd.c
@@ -6,10 +6,10 @@
 
 char *getcwd(char *buf, size_t size)
 {
-	char tmp[PATH_MAX];
+	char tmp[buf ? 1 : PATH_MAX];
 	if (!buf) {
 		buf = tmp;
-		size = PATH_MAX;
+		size = sizeof tmp;
 	} else if (!size) {
 		errno = EINVAL;
 		return 0;