------- Comment #4 from xavier dot guerin at imag dot fr 2010-02-07 12:32
-------
I checked GCC 4.4.2 and the issue still exists. It's extremely easy to check,
and I actually pinned the issue. I don't mind helping more (and I guess I'll
have to do it by myself anyway), but I'm completely ignorant concerning
compilation stuff.
Basically, the issue is as follows. Let's say we have this situation (note that
he behavior of function() is irrelevant) compiled for a mips32 architecture :
int function (int n, ...)
{
}
int main (void)
{
int32_t i32;
int64_t i64_0, i64_1;
function (3, i64_0, i32, i64_1);
return 0;
}
###### Caller behavior ######
In that case, main prepare the va_list. Right before calling function(), the
stack looks like this:
SP-40 [ X | X | X | X | n | X | upper (i64_1) | lower (i64_1) | X | RA ] SP
whereas upper (i64_0) and lower (i64_0) are stored in registers a2 and a3.
Please note that GCC inserts a bubble between 'n' and 'upper(i64_1)'. At
first, I supposed this was for double-word alignment purpose, but in my case
the address of 'upper (i64_1)' is not double-word aligned.
###### Callee behavior ######
Anyhow, the callee is waiting for the following stack pattern when mashalling
the varargs:
SP-40 [ X | X | X | X | n | upper (i64_1) | lower (i64_1) | X | X | RA ] SP
which is the same configuration but without the bubble. As see it, the callee
code must be correct since it refers to the algorithm described in function
mips_gimplify_va_arg_expr(), line 5235 of the mips.c files, while the caller
code wrongfully inserts a bubble to correct a padding problem that does not
exit.
I think this should shed some lights on the issue I'm encountering. Maybe
somehow could tell me where I can found the va_list preparation code in the
mips.c file.
Thanks in advance for your help,
Xavier
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39640
