tree 4fe0c1142109ff962183ab7c7ab645c99d5db765
parent 5978eb703ce0e64dd778a88c1ffffb76fe5e2202
author Rich Felker <dalias@aerifal.cx> 1459222877 -0400
committer Rich Felker <dalias@aerifal.cx> 1459222877 -0400

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.