* Re: [PATCH] tcg/aarch64: Apple does not align __int128_t in even registers
2024-02-16 21:45 [PATCH] tcg/aarch64: Apple does not align __int128_t in even registers Richard Henderson
@ 2024-02-18 10:59 ` Philippe Mathieu-Daudé
0 siblings, 0 replies; 2+ messages in thread
From: Philippe Mathieu-Daudé @ 2024-02-18 10:59 UTC (permalink / raw)
To: Richard Henderson, qemu-devel; +Cc: qemu-stable
On 16/2/24 22:45, Richard Henderson wrote:
Please include your comment
https://gitlab.com/qemu-project/qemu/-/issues/2169#note_1777369822
---
Apple differs from the standard ABI in the alignment of __int128_t.
From Apple's documentation:
When passing an argument with 16-byte alignment in integer registers,
Apple platforms allow the argument to start in an odd-numbered xN
register. The standard ABI requires it to begin in an even-numbered
xN register.
This is confirmed with a simple test:
void g(int w, __int128_t x, int y);
void h(void)
{
g(-1, 0, 1);
}
which produces
mov w0, #-1
mov x1, #0
mov x2, #0
mov w3, #1
bl _g
using Apple clang version 14.0.0 (clang-1400.0.29.202). Note
that the x argument (the zeros) is loaded into x1 and x2 and
the y argument is loaded into w3.
On Linux, using the standard ARM ABI, this compiles to
mov w4, 1
mov x2, 0
mov x3, 0
mov w0, -1
bl g
Note that the x argument is loaded into x2 and x3, and the y
argument is loaded into w4.
The TCG JIT must be taught about this difference for MacOS.
---
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> Cc: qemu-stable@nongnu.org
> Fixes: 5427a9a7604 ("tcg: Add TCG_TARGET_CALL_{RET,ARG}_I128")
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2169
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>
> See the gitlab issue for complete discussion of the ABI.
>
> r~
>
> ---
> tcg/aarch64/tcg-target.h | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/tcg/aarch64/tcg-target.h b/tcg/aarch64/tcg-target.h
> index ef5ebe91bd..85d5746e47 100644
> --- a/tcg/aarch64/tcg-target.h
> +++ b/tcg/aarch64/tcg-target.h
> @@ -55,7 +55,11 @@ typedef enum {
> #define TCG_TARGET_CALL_STACK_OFFSET 0
> #define TCG_TARGET_CALL_ARG_I32 TCG_CALL_ARG_NORMAL
> #define TCG_TARGET_CALL_ARG_I64 TCG_CALL_ARG_NORMAL
> -#define TCG_TARGET_CALL_ARG_I128 TCG_CALL_ARG_EVEN
> +#ifdef CONFIG_DARWIN
> +# define TCG_TARGET_CALL_ARG_I128 TCG_CALL_ARG_NORMAL
> +#else
> +# define TCG_TARGET_CALL_ARG_I128 TCG_CALL_ARG_EVEN
> +#endif
> #define TCG_TARGET_CALL_RET_I128 TCG_CALL_RET_NORMAL
>
> #define have_lse (cpuinfo & CPUINFO_LSE)
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