[x265] [PATCH 01/12] AArch64: Fix costCoeffNxN test on Apple Silicon

[Pop, Sebastian]

Ok.
Thanks for the patch.

Sebastian

On 5/2/24, 4:23 PM, "x265-devel on behalf of Hari Limaye" <x265-devel-bounces at videolan.org <mailto:x265-devel-bounces at videolan.org> on behalf of hari.limaye at arm.com <mailto:hari.limaye at arm.com>> wrote:


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The assembly routine x265_costCoeffNxN_neon is buggy and produces an
incorrect result on Apple Silicon, causing the pixel testbench to fail
on these platforms.


x265_costCoeffNxN assumes that parameter `int subPosBase`, the second
parameter of type `int` passed on the stack, is at position `sp + 8`;
this assumption is consistent with the AArch64 PCS, as arguments smaller
than 8 bytes are widened to 8 bytes (aapcs64 6.8.2 C.16).
However arm64e diverges from AAPCS64: 'Function arguments may consume
slots on the stack that are not multiples of 8 bytes'.
---
source/common/aarch64/asm.S | 12 +++++++++++-
source/common/aarch64/pixel-util.S | 4 ++--
2 files changed, 13 insertions(+), 3 deletions(-)


diff --git a/source/common/aarch64/asm.S b/source/common/aarch64/asm.S
index ce0668103..742978631 100644
--- a/source/common/aarch64/asm.S
+++ b/source/common/aarch64/asm.S
@@ -72,6 +72,16 @@


#define PFX_C(name) JOIN(JOIN(JOIN(EXTERN_ASM, X265_NS), _), name)


+// Alignment of stack arguments of size less than 8 bytes.
+#ifdef __APPLE__
+#define STACK_ARG_ALIGNMENT 4
+#else
+#define STACK_ARG_ALIGNMENT 8
+#endif
+
+// Get offset from SP of stack argument at index `idx`.
+#define STACK_ARG_OFFSET(idx) (idx * STACK_ARG_ALIGNMENT)
+
#ifdef __APPLE__
.macro endfunc
ELF .size \name, . - \name
@@ -184,4 +194,4 @@ ELF .size \name, . - \name
vtrn \t3, \t4, \s3, \s4
.endm


-#endif
\ No newline at end of file
+#endif
diff --git a/source/common/aarch64/pixel-util.S b/source/common/aarch64/pixel-util.S
index 9b3c11504..378c6891c 100644
--- a/source/common/aarch64/pixel-util.S
+++ b/source/common/aarch64/pixel-util.S
@@ -2311,7 +2311,7 @@ endfunc
// uint8_t *baseCtx, // x6
// int offset, // x7
// int scanPosSigOff, // sp
-// int subPosBase) // sp + 8
+// int subPosBase) // sp + 8, or sp + 4 on APPLE
function PFX(costCoeffNxN_neon)
// abs(coeff)
add x2, x2, x2
@@ -2410,7 +2410,7 @@ function PFX(costCoeffNxN_neon)
add x4, x4, x15
str h2, [x13] // absCoeff[numNonZero] = tmpCoeff[blkPos]


- ldr x9, [sp, #8] // subPosBase
+ ldr x9, [sp, #STACK_ARG_OFFSET(1)] // subPosBase
uxth w9, w9
cmp w9, #0
cset x2, eq
--
2.42.1


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