Hi list,
I had a chance to look to the remaining ppc64/ppc32 test case failure in
ltrace. I believe this is a general problem, when you take exactly this
example to x86_64/i386 it breaks, too.
Here's the reproducer program, ww.c:
struct ww { int a; int *pa; };
#ifdef LIB
int ble (void *x) { return 1; }
#else
int ble (void *x);
#endif
#ifndef LIB
int main () {
struct ww x;
x.a = 3;
x.pa = &x.a;
return ble (&x);
}
#endif
And corresponding config file, ww.conf:
void ble(struct(int,int*)*)
Use normal steps to compile ltrace in 64-bit mode, then compile the test
case like this:
$ gcc -DLIB -fpic -shared ~/ww.c -o libww.so
$ gcc -ULIB ~/ww.c ./libww.so -o ww
$ gcc -DLIB -fpic -shared -m32 ~/ww.c -o libww32.so
$ gcc -ULIB -m32 ~/ww.c ./libww32.so -o ww32
And run (output trimmed):
# ./ltrace -F ~/ww.conf ./ww
ble({ 3, 3 }) = <void>
# ./ltrace -F ~/ww.conf ./ww32
ble({ 3, -2311104 }) = <void>
The value -2311104 is some random bit of the process address space, it
might end up being "?" if the region it tries to read is inaccessible.
The problem here is that 64-bit ltrace thinks the pointer alignment is 8
bytes, but it's tracing 32-bit inferior that thinks it should rather be
4. In this particular case I can go to read_config_file.c and hard-code
pointer alignment to 4 bytes, which fixes it. At least on ppc, on x8664
this didn't work for me for some reason, it must be more or differently
buggy.
So,
- front end needs to leave these sorts of decisions, like pointer
alignment, to back end. The simple trick with alignof won't work in
general.
- front end needs to know it may need to precompute 32-bit layouts even
on 64-bit.
- which means that i386 and x86_64 can no longer be totally separate
backends, at least not the way they are now, or at least x86_64 has to
include i386. I'm thinking it shouldn't be terribly hard to merge them,
ppc and s390 have always been like that AFAIK.
Well, tell me your thoughts.
PM
_______________________________________________
Ltrace-devel mailing list
[email protected]
http://lists.alioth.debian.org/mailman/listinfo/ltrace-devel
