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fix undefined pointer comparison in stdio-internal __toread 

the comparison f->wpos > f->buf has undefined behavior when f->wpos is
a null pointer, despite the intuition (and actual compiler behavior,
for all known compilers) being that NULL > ptr is false for all valid
pointers ptr.

the purpose of the comparison is to determine if the write buffer is
non-empty, and the idiom used elsewhere for that is comparison against
f->wbase, which is either a null pointer when not writing, or equal to
f->buf when writing. in the former case, both f->wpos and f->wbase are
null; in the latter they are both non-null and point into the same
array.
This commit is contained in:
Rich Felker 2016-03-28 23:41:17 -04:00
parent 5978eb703c
commit 6d1a3dfeaf
1 changed files with 1 additions and 1 deletions
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2
src/stdio/__toread.c
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@ -3,7 +3,7 @@
int __toread(FILE *f)
{
f->mode |= f->mode-1;
if (f->wpos > f->buf) f->write(f, 0, 0);
if (f->wpos > f->wbase) f->write(f, 0, 0);
f->wpos = f->wbase = f->wend = 0;
if (f->flags & F_NORD) {
f->flags |= F_ERR;