[arm][RFC] PR target/88469 fix incorrect argument passing with 64-bit bitfields

[Bernd Edlinger]

Hi,

I know I am a bit late on the party.

But I have a question...

Consider this test case:

$ cat test.c
struct s {
  int a, b;
} __attribute__((aligned(8)));

struct s f0;
int f(int a, int b, int c, int d, int e, struct s f)
{
  f0 = f;
  return __alignof(f);
}

$ arm-linux-gnueabihf-gcc -march=armv5te -O3 -S test.c
$ cat test.s
f:
	@ args = 12, pretend = 0, frame = 0
	@ frame_needed = 0, uses_anonymous_args = 0
	@ link register save eliminated.
	push	{r4, r5}
	mov	r0, #8
	ldrd	r4, [sp, #12]
	ldr	r3, .L4
	strd	r4, [r3]
	pop	{r4, r5}
	bx	lr

I am pretty sure, although there is no warning, this ABI changed in GCC 5.2

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0473m/dom1361290002364.html
says:

"In ARMv5TE, or in ARMv6 when SCTLR.U is 0, LDRD and STRD doubleword data transfers must be
eight-byte aligned.  Use ALIGN 8 before memory allocation directives such as DCQ if the data
is to be accessed using LDRD or STRD.  This is not required in ARMv6 when SCTLR.U is 1, or in
ARMv7, because in these versions, doubleword data transfers can be word-aligned."


So isn't this wrong code, returning 8 for alignof when it is really 4,
and wouldn't it crash on armv5 and armv6 with SCTLR.U=0 ?


Bernd.