On Tue, Feb 13, 2018 at 5:16 PM, Sean McGovern <gsean...@gmail.com> wrote:
>
> I discovered this while doing a full valgrind FATE run on a POWER7
> machine -- among others, fate-noproxy failed.
>
> The result for the noproxy test in this case makes me believe it is
> using the aforementioned behaviour of memcmp():
>
> ==47650== Memcheck, a memory error detector
> ==47650== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
> ==47650== Using Valgrind-3.12.0 and LibVEX; rerun with -h for copyright info
> ==47650== Command: /home/seanmcg/build/libav-gcc7/libavformat/tests/noproxy
> ==47650==
> ==47650== Invalid read of size 8
> ==47650==    at 0x1000646C: match_host_pattern (network.c:255)
> ==47650==    by 0x1000646C: ff_http_match_no_proxy (network.c:284)
> ==47650==    by 0x100059CF: test (noproxy.c:25)
> ==47650==    by 0x100057BB: main (noproxy.c:34)
> ==47650==  Address 0x4480054 is 20 bytes inside a block of size 23 alloc'd
> ==47650==    at 0x40861E4: malloc (vg_replace_malloc.c:298)
> ==47650==    by 0x4088AD3: realloc (vg_replace_malloc.c:785)
> ==47650==    by 0x100A9A2F: av_realloc (mem.c:116)
> ==47650==    by 0x100A9A2F: av_strdup (mem.c:215)
> ==47650==    by 0x10006267: ff_http_match_no_proxy (network.c:272)
> ==47650==    by 0x100059CF: test (noproxy.c:25)
> ==47650==    by 0x100057BB: main (noproxy.c:34)
> ==47650==
>
> <..snipped for brevity, pattern repeats for each test..>
>
> I found the following bug reports which seemed relevant in the GCC Bugzilla:
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52171 and
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78257
>
> I don't think this is a compiler bug or cargo-culting, although Clang
> does not appear to exhibit this behaviour.
>

How is this not a compiler bug if valid C code results in an
out-of-bounds access due to some optimization?

- Hendrik
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