Ok, I'm now posting this as an official bug.

gcc 3.1 and higher (including current CVS HEAD aka gcc-3.3) have a problem passing structs (not struct pointers) to functions when those structs contain static char arrays, and -march=i686 or higher is used (-march=athlon-{xp,mp} seems to be exempt for some reason, though -march=athlon is affected).  Basically, the struct that the function receives has garbage contents.

Structs with static arrays of other types (such as int or float) do not seem to trigger this bug.

Release:
unknown

Environment:
System: Linux valhalla 2.4.18-1 #4 Mon Jun 10 22:08:58 CDT 2002 i686 AuthenticAMD
Architecture: i686

        <machine, os, target, libraries (multiple lines)>
host: i386-incept-linux-gnu
build: i386-incept-linux-gnu
target: i386-incept-linux-gnu
configured with: ../gcc-3.1.1/configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var --enable-version-specific-runtime-libs --enable-threads=posix --enable-languages=c,c++ --enable-shared --with-system-zlib --with-__cxa_atexit --host=i386-incept-linux-gnu --target=i386-incept-linux-gnu --build=i386-incept-linux-gnu

How-To-Repeat:
Below is a small testcase (same .c file that was used to generate the attached .i file).

--Begin testcase.c--
#include <stdio.h>

struct abba {
    char str[128];
};

void test(struct abba ke)
{
    printf("%s\n", ke.str);
}

int main()
{
    struct abba ke;

    strcpy(ke.str, "DOH");
    test(ke);
}
--End testcase.c--

[ root@valhalla /usr/src ] # gcc -O2 -march=i686 \
testcase.c -o testcase
[ root@valhalla /usr/src ] # ./testcase
ج@`ûÿ¿¨G@`a    @ÈØ@8K@7û@Xýÿ¿/
[ root@valhalla /usr/src ] # gcc -O2 -march=i486 \
testcase.c -o testcase
[ root@valhalla /usr/src ] # ./testcase
DOH
[ root@valhalla /usr/src ] # gcc -march=i686 testcase.c \
-o testcase
[ root@valhalla /usr/src ] # ./testcase
ûÿ¿¨G@`a        @ÈØ@8K@7û@Xýÿ¿/