On 18/3/25 23:02, Pierrick Bouvier wrote:
On 3/18/25 11:50, Philippe Mathieu-Daudé wrote:
On 18/3/25 05:51, Pierrick Bouvier wrote:
This will affect zregs field for aarch32.
This field is used for MVE and SVE implementations. MVE implementation
is clipping index value to 0 or 1 for zregs[*].d[],
so we should not touch the rest of data in this case anyway.
We should describe why it is safe for migration.
I.e. vmstate_za depends on za_needed() -> SME, not included in 32-bit
cpus, etc.
Should we update target/arm/machine.c in this same patch, or a
preliminary one?
vmstate_za definition and inclusion in vmstate_arm_cpu is under #ifdef
TARGET_AARCH64. In this case (TARGET_AARCH64), ARM_MAX_VQ was already
defined as 16, so there should not be any change.
I'm not saying this is invalid, I'm trying to say we need to document
why it is safe.
Other values depending on ARM_MAX_VQ, for migration, are as well under
TARGET_AARCH64 ifdefs (vmstate_zreg_hi_reg, vmstate_preg_reg,
vmstate_vreg).
And for vmstate_vfp, which is present for aarch32 as well, the size of
data under each register is specifically set to 2.
VMSTATE_UINT64_SUB_ARRAY(env.vfp.zregs[0].d, ARMCPU, 0, 2)
So even if storage has more space, it should not impact any usage of it.
Even though this change is trivial, I didn't do it blindly to "make it
compile" and I checked the various usages of ARM_MAX_VQ and zregs, and I
didn't see anything that seems to be a problem.
You did the analysis once, let's add it in the commit description so
other developers looking at this commit won't have to do it again.
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@xxxxxxxxxx>
---
target/arm/cpu.h | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)
diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index 27a0d4550f2..00f78d64bd8 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -169,11 +169,7 @@ typedef struct ARMGenericTimer {
* Align the data for use with TCG host vector operations.
*/
-#ifdef TARGET_AARCH64
-# define ARM_MAX_VQ 16
-#else
-# define ARM_MAX_VQ 1
-#endif
+#define ARM_MAX_VQ 16
typedef struct ARMVectorReg {
uint64_t d[2 * ARM_MAX_VQ] QEMU_ALIGNED(16);
