[MLton] Re: MLton and shared libraries
Wed, 20 Apr 2005 11:11:38 -0700
> Program received signal SIGSEGV, Segmentation fault.
> Chunk0 () at test.1.c:5084
> 5084 S(Word32, 0) = 0;
> Since S is defined as
> #define S(ty, i) *(ty*)(StackTop + (i))
> in c-chunk.h, this is merely a write to the first element
> of the stack. Which shouldn't be able to fail unless the
> GC hasn't been initialized - I think.
That seems right to me.
> Apropos, should gcState.isOriginal be true after a call
> to GC_init ?
Yes, unless the command line has "@MLton load-world ...".
> Anyways, Chunk 0 is the only chunk in test.1.c and the
> offending line is in the very end:
> S(Word32, 0) = 0; ;;; <- HERE
> Push (4);
> GC_gc (GCState, 0x45C, 0x0, __FILE__, __LINE__);
> Push (-4);
> goto L_4;
> case 0:
> goto L_0;
This looks like the first call to the GC in the program, which is to
make space to allocate the globals (presumably there is a limit check
that fails and jumps to L_1). The "S(Word32, 0) = 0" stores the
return address (0) on the stack. The return address (0) is handled
by the "case 0:", which will jump to the right return code (L_0),
although in this case, the program isn't multithreaded, so MLton knows
to generate code to fall through to the L_0 block without ever
checking the return address.
Here are some suggestions.
* step through GC_init and make sure it's actually running and that
the stack is allocated.
* recompile the runtime with various debugging options
(DEBUG_DETAILED, DEBUG_STACKS, ...).
* step through the MLton-generated C code starting as soon as Chunk0
is entered and verify that the stack looks good.