<div dir="ltr"><br><br><div class="gmail_quote">On Wed, Jul 11, 2012 at 9:55 PM, Bardur Arantsson <span dir="ltr"><<a href="mailto:spam@scientician.net" target="_blank">spam@scientician.net</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="im">On 07/11/2012 05:12 PM, Michael Snoyman wrote:<br>
><br>
> Thanks for the feedback. However, looking at sqlite3.c, I see the<br>
> necessary #include statements:<br>
><br>
> #include <sys/types.h><br>
> #include <sys/stat.h><br>
> #include <unistd.h><br>
><br>
> I'm confident that none of my code is making calls to stat/stat64 via<br>
> the FFI. In case it makes a difference, this problem also disappears<br>
> if I compile the library against the system copy of sqlite3 instead of<br>
> using the C source.<br>
<br>
</div>You may need some extra defines, see the comments in "man stat64".<br>
<br>
Regards,<br>
<br>
<br>
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</blockquote></div><br><div>I've come up with a minimal example that demonstrates this problem. The crux of the matter is the following C code:</div><div><br></div><div><div> #include <sys/types.h></div><div>
#include <sys/stat.h></div><div> #include <unistd.h></div><div> #include <stdio.h></div><div> </div><div> typedef int stat_func(const char*, struct stat*);</div><div> </div><div> stat_func *foo = &stat;</div>
<div> </div><div> void stat_test(void)</div><div> {</div><div> <span class="Apple-tab-span" style="white-space:pre"> </span>struct stat buf;</div><div> </div><div> <span class="Apple-tab-span" style="white-space:pre"> </span>printf("About to stat-test.c\n");</div>
<div> <span class="Apple-tab-span" style="white-space:pre"> </span>foo("stat-test.c", &buf);</div><div> <span class="Apple-tab-span" style="white-space:pre"> </span>printf("Done\n");</div><div>
}</div></div><div><br></div><div>As you can see, all of the include statements are present as necessary. The code compiles just fine with -Wall -Werror. And when you compile the Haskell code as well, everything works just fine. But if you follow these steps, you can reproduce the error I saw:</div>
<div><br></div><div>* Unpack the attached tarball</div><div>* `cabal install` in that folder</div><div>* `runghc main.hs` from the `exe` folder</div><div><br></div><div>On my system at least, I get:</div><div><br></div><div>
<div> main.hs: /home/ubuntu/.cabal/lib/stat-test-0.1.0.0/ghc-7.4.1/HSstat-test-0.1.0.0.o: unknown symbol `stat'</div><div> main.hs: main.hs: unable to load package `stat-test-0.1.0.0'</div></div><div><br></div>
<div>One thing I noticed is that I needed to use a function pointer to trigger the bug. When I called `stat` directly the in stat_test function, gcc automatically inlined the call, so that the disassessmbled code just showed a `moveq` (i.e., it's making the system call directly). But using a function pointer, we're avoiding the inlining. I believe this is why this issue only came up with the sqlite3 upgrade: previous versions did not use a function pointer, but rather hard-coded in how to make a stat call.</div>
<div><br></div><div>Does this expose any other possibilities?</div><div><br></div><div>Michael</div></div>