On Sun, 13 Mar 2016 00:26:41 +0100
Carl-Daniel Hailfinger <c-d.hailfinger.devel.2...@gmx.net> wrote:
> On 13.03.2016 00:05, Stefan Tauner wrote:
> > This came up when I was testing if building on SunOS still works
> > on the buildbot's instance of OmniOS r151014 which is based on illumos.
> >
> > The fix is
> > - to link against libnsl
> > - a small C type fix in ich_descriptor_tool
> >
> > Signed-off-by: Stefan Tauner <stefan.tau...@alumni.tuwien.ac.at>
> > Acked-by: Stefan Tauner <stefan.tau...@alumni.tuwien.ac.at>
> >
> > diff --git a/util/ich_descriptors_tool/ich_descriptors_tool.c
> > b/util/ich_descriptors_tool/ich_descriptors_tool.c
> > index c3d9ba1..ad3b6f0 100644
> > --- a/util/ich_descriptors_tool/ich_descriptors_tool.c
> > +++ b/util/ich_descriptors_tool/ich_descriptors_tool.c
> > @@ -170,7 +170,7 @@ int main(int argc, char *argv[])
> > usage(argv, "Seeking to the end of the file failed");
> >
> > #ifdef HAVE_MMAP
> > - buf = mmap(NULL, len, PROT_READ, MAP_PRIVATE, fd, 0);
> > + buf = (uint32_t *)mmap(NULL, len, PROT_READ, MAP_PRIVATE, fd, 0);
>
> The compiler may require that to stop complaining, but AFAICS there is a
> real bug behind this. buf is sometimes casted to uint8_t *, and unless
> I'm too sleepy already, this buffer violates the strict aliasing rules.
> We can solve this with -fno-strict-aliasing, or fix the code. With a
> code fix, in theory the problem should go away.
While this is true it does not make much sense to try to fix it:
- all accesses are read-only. The compiler can re-order as much as it
wants, we won't get wrong results. No compiler writers however mean
will make this explode. And that's the only potential problem with
aliasing.
- ich_descriptor.c intentionally uses undefined behavior by writing to
some struct members and reading it through others to spare us from
bit-shifting/masking. That was discussed at length back when I added
it and since we use the code on x86 only it is fine.
>
>
> > if (buf == (void *) -1)
> > #endif
> > {
>
>
> Side note (no need to fix this right now)
> util/ich_descriptors_tool/ich_descriptors_tool.c:182
> if (len != read(fd, buf, len))
> usage(argv, "Seeking to the end of the file
> failed");
> Somehow that error message doesn't fit with the code.
Copy and paste error from :170. Fixed in tested_stuff, thanks!
--
Kind regards/Mit freundlichen Grüßen, Stefan Tauner
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