From: Richard Henderson <richard.henderson@linaro.org>

Add an interface function to extract the digested vector length
rather than the raw zcr_el[1] value.  This fixes an incorrect
return from do_prctl_set_vl where we didn't take into account
the set of vector lengths supported by the cpu.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220607203306.657998-3-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 linux-user/aarch64/target_prctl.h | 20 +++++++++++++-------
 target/arm/cpu.h                  | 11 +++++++++++
 linux-user/aarch64/signal.c       |  4 ++--
 3 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/linux-user/aarch64/target_prctl.h b/linux-user/aarch64/target_prctl.h
index 3f5a5d3933a..1d440ffbea4 100644
--- a/linux-user/aarch64/target_prctl.h
+++ b/linux-user/aarch64/target_prctl.h
@@ -10,7 +10,7 @@ static abi_long do_prctl_get_vl(CPUArchState *env)
 {
     ARMCPU *cpu = env_archcpu(env);
     if (cpu_isar_feature(aa64_sve, cpu)) {
-        return ((cpu->env.vfp.zcr_el[1] & 0xf) + 1) * 16;
+        return sve_vq(env) * 16;
     }
     return -TARGET_EINVAL;
 }
@@ -25,18 +25,24 @@ static abi_long do_prctl_set_vl(CPUArchState *env, abi_long arg2)
      */
     if (cpu_isar_feature(aa64_sve, env_archcpu(env))
         && arg2 >= 0 && arg2 <= 512 * 16 && !(arg2 & 15)) {
-        ARMCPU *cpu = env_archcpu(env);
         uint32_t vq, old_vq;
 
-        old_vq = (env->vfp.zcr_el[1] & 0xf) + 1;
-        vq = MAX(arg2 / 16, 1);
-        vq = MIN(vq, cpu->sve_max_vq);
+        old_vq = sve_vq(env);
 
+        /*
+         * Bound the value of arg2, so that we know that it fits into
+         * the 4-bit field in ZCR_EL1.  Rely on the hflags rebuild to
+         * sort out the length supported by the cpu.
+         */
+        vq = MAX(arg2 / 16, 1);
+        vq = MIN(vq, ARM_MAX_VQ);
+        env->vfp.zcr_el[1] = vq - 1;
+        arm_rebuild_hflags(env);
+
+        vq = sve_vq(env);
         if (vq < old_vq) {
             aarch64_sve_narrow_vq(env, vq);
         }
-        env->vfp.zcr_el[1] = vq - 1;
-        arm_rebuild_hflags(env);
         return vq * 16;
     }
     return -TARGET_EINVAL;
diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index e791ffdd6b6..f5af88b686d 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -3286,6 +3286,17 @@ static inline int cpu_mmu_index(CPUARMState *env, bool ifetch)
     return EX_TBFLAG_ANY(env->hflags, MMUIDX);
 }
 
+/**
+ * sve_vq
+ * @env: the cpu context
+ *
+ * Return the VL cached within env->hflags, in units of quadwords.
+ */
+static inline int sve_vq(CPUARMState *env)
+{
+    return EX_TBFLAG_A64(env->hflags, VL) + 1;
+}
+
 static inline bool bswap_code(bool sctlr_b)
 {
 #ifdef CONFIG_USER_ONLY
diff --git a/linux-user/aarch64/signal.c b/linux-user/aarch64/signal.c
index 7de4c96eb9d..7da0e36c6d4 100644
--- a/linux-user/aarch64/signal.c
+++ b/linux-user/aarch64/signal.c
@@ -315,7 +315,7 @@ static int target_restore_sigframe(CPUARMState *env,
 
         case TARGET_SVE_MAGIC:
             if (cpu_isar_feature(aa64_sve, env_archcpu(env))) {
-                vq = (env->vfp.zcr_el[1] & 0xf) + 1;
+                vq = sve_vq(env);
                 sve_size = QEMU_ALIGN_UP(TARGET_SVE_SIG_CONTEXT_SIZE(vq), 16);
                 if (!sve && size == sve_size) {
                     sve = (struct target_sve_context *)ctx;
@@ -434,7 +434,7 @@ static void target_setup_frame(int usig, struct target_sigaction *ka,
 
     /* SVE state needs saving only if it exists.  */
     if (cpu_isar_feature(aa64_sve, env_archcpu(env))) {
-        vq = (env->vfp.zcr_el[1] & 0xf) + 1;
+        vq = sve_vq(env);
         sve_size = QEMU_ALIGN_UP(TARGET_SVE_SIG_CONTEXT_SIZE(vq), 16);
         sve_ofs = alloc_sigframe_space(sve_size, &layout);
     }
-- 
2.25.1