Compiling the following C source:
struct test {
int a;
};
static inline void test2(struct test *t)
{
register int a asm("r0") = (int) t;
asm volatile ("swi #0" :: "r" (a));
}
void test1(void)
{
struct test t;
t.a = 0;
test2(&t);
}
with "arm-elf-gcc test.c -S -O1" produces the following assembler output:
.file "test.c"
.text
.align 2
.global test1
.type test1, %function
test1:
@ args = 0, pretend = 0, frame = 4
@ frame_needed = 0, uses_anonymous_args = 0
@ link register save eliminated.
sub sp, sp, #4
mov r0, sp
@ 8 "test.c" 1
swi #0
@ 0 "" 2
add sp, sp, #4
bx lr
.size test1, .-test1
.ident "GCC: (GNU) 4.4.1"
For the call to test2(), the pointer to struct test t is properly set up, but
the content of the struct (t.a = 0) isn't. This is the case for -O1, -O2, -Os
and -O3, but not for -O0, where gcc produces working code.
arm-elf-gcc -v:
Using built-in specs.
Target: arm-elf
Configured with: /var/tmp/gcc.uZt0/gcc-4.4.1/configure --enable-languages=c
--with-mpfr=/usr/local --without-headers --target=arm-elf
--prefix=/usr/local/arm-elf --with-local-prefix=/usr/local/arm-elf
--disable-werror --enable-multilib --enable-shared --disable-nls
--disable-libssp --with-arch=armv4t --with-cpu=arm7tdmi-s
Thread model: single
gcc version 4.4.1 (GCC)
--
Summary: gcc produces broken code when passing struct pointer to
static inline function with asm()
Product: gcc
Version: 4.4.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: inline-asm
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: agraf at znc dot in
GCC target triplet: arm-elf
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42984
