On Thu, Jul 12, 2012 at 06:29:41PM +0300, Michael Snoyman wrote:
I've come up with a minimal example that demonstrates this problem. The crux of the matter is the following C code:
#include
#include #include #include typedef int stat_func(const char*, struct stat*);
stat_func *foo = &stat;
void stat_test(void) { struct stat buf;
printf("About to stat-test.c\n"); foo("stat-test.c", &buf); printf("Done\n"); }
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:
* Unpack the attached tarball * `cabal install` in that folder * `runghc main.hs` from the `exe` folder
On my system at least, I get:
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' main.hs: main.hs: unable to load package `stat-test-0.1.0.0'
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.
Does this expose any other possibilities?
Michael
Are you trying this on a 32 bit system? And when you compiled that C program, did you try to add -D_FILE_OFFSET_BITS=64 -D_LARGEFILE64_SOURCE to the compile command? When I define those the resulting object file from your example correctly references stat64 instead of stat.