fix multiple stdio functions' behavior on zero-length operations

previously, fgets, fputs, fread, and fwrite completely omitted locking
and access to the FILE object when their arguments yielded a zero
length read or write operation independent of the FILE state. this
optimization was invalid; it wrongly skipped marking the stream as
byte-oriented (a C conformance bug) and exposed observably missing
synchronization (a POSIX conformance bug) where one of these functions
could wrongly complete despite another thread provably holding the
lock.

1 files changed, 0 insertions, 1 deletions

diff --git a/src/stdio/fwrite.c b/src/stdio/fwrite.c
index d5f6542d..81ec271e 100644
--- a/src/stdio/fwrite.c
+++ b/src/stdio/fwrite.c
@@ -28,7 +28,6 @@ size_t __fwritex(const unsigned char *restrict s, size_t l, FILE *restrict f)
 size_t fwrite(const void *restrict src, size_t size, size_t nmemb, FILE *restrict f)
 {
 	size_t k, l = size*nmemb;
-	if (!l) return l;
 	FLOCK(f);
 	k = __fwritex(src, l, f);
 	FUNLOCK(f);