On 04 March 2005 17:32, Kurt Roeckx wrote:
> I have no idea what ghc has too do with gcc,
A bit of background: GHC uses gcc as a backend compiler. GHC generates
C code that is compiled using gcc (we also have a native code generator
for some platforms; but not for x86_64 yet).
> or what the problem exactly is.
The problem is that gcc generates incorrect code for C code that uses
global register variables. You won't have noticed this, because most
programs don't use global register variables. GHC uses global register
variables to speed up the generated code.
> We have very little problems with gcc for the debian
> amd64 port. Our default compiler is still 3.3. This builds
> almost everything without problems, however we build a few
> mozilla packages with gcc-3.4.
>
> All I can tell is that ghc6 seems to be working on debian amd64.
> It can build itself and things like that.
That build of ghc6 is what we call "unregisterised": it doesn't make use
of register variables to speed up the generated code. IOW, it generates
plain ANSI C code, which gcc compiles fine.
> Can someone please give a test case (and show what to do) to see
> what is wrong?
Ok, here's a really simple example:
$ cat bug.c
register void * R1 __asm__("%r13");
extern void g(void);
static void f(void) {
R1 = g;
goto *R1;
}
$ gcc -S -O bug.c
$
And take a look at the generated assembly for the function f:
f:
.LFB2:
movl $g, %eax
jmp *%rax
Note that the assignment to the global variable R1 has been lost. It
works fine on x86 though: change the register variable to %esi and try
it.
> Out current default compiler in debian is:
> gcc version 3.3.5 (Debian 1:3.3.5-8)
>
> The gcc 3.4 version is:
> gcc version 3.4.4 20050203 (prerelease) (Debian 3.4.3-9)
>
> And ghc6 is at version 6.2.2-3.
I'm going to try with different versions of gcc. I've just submitted
this bug report to the gcc guys.
Cheers,
Simon
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