path: root/src/stdio/fread.c
diff options
authorRich Felker <>2014-09-04 22:21:17 -0400
committerRich Felker <>2014-09-04 22:21:17 -0400
commit6e2bb7acf42589fb7130b039d0623e2ca42503dd (patch)
tree7af4719cfa84bc8cf0c6fa73fdca42035eaf03e9 /src/stdio/fread.c
parent402611c3ba3be5b3b0486835d98e22ac7ced2722 (diff)
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.
Diffstat (limited to 'src/stdio/fread.c')
1 files changed, 2 insertions, 3 deletions
diff --git a/src/stdio/fread.c b/src/stdio/fread.c
index c461256c..33a65f58 100644
--- a/src/stdio/fread.c
+++ b/src/stdio/fread.c
@@ -8,11 +8,10 @@ size_t fread(void *restrict destv, size_t size, size_t nmemb, FILE *restrict f)
unsigned char *dest = destv;
size_t len = size*nmemb, l = len, k;
- /* Never touch the file if length is zero.. */
- if (!l) return 0;
+ f->mode |= f->mode-1;
if (f->rend - f->rpos > 0) {
/* First exhaust the buffer. */
k = MIN(f->rend - f->rpos, l);