diff --git a/risu.h b/risu.h
index 3cad3d5..bdb70c1 100644
--- a/risu.h
+++ b/risu.h
@@ -23,6 +23,7 @@
 extern const struct option * const arch_long_opts;
 extern const char * const arch_extra_help;
 void process_arch_opt(int opt, const char *arg);
+void arch_init(void);
 #define FIRST_ARCH_OPT   0x100
 
 /* GCC computed include to pull in the correct risu_reginfo_*.h for
diff --git a/risu.c b/risu.c
index a70b778..1c096a8 100644
--- a/risu.c
+++ b/risu.c
@@ -617,6 +617,9 @@ int main(int argc, char **argv)
 
     load_image(imgfile);
 
+    /* E.g. select requested SVE vector length. */
+    arch_init();
+
     if (ismaster) {
         return master();
     } else {
diff --git a/risu_reginfo_aarch64.c b/risu_reginfo_aarch64.c
index a1020ac..fb8e11a 100644
--- a/risu_reginfo_aarch64.c
+++ b/risu_reginfo_aarch64.c
@@ -44,8 +44,6 @@ const char * const arch_extra_help
 void process_arch_opt(int opt, const char *arg)
 {
 #ifdef SVE_MAGIC
-    long want, got;
-
     assert(opt == FIRST_ARCH_OPT);
     test_sve = strtol(arg, 0, 10);
 
@@ -53,22 +51,37 @@ void process_arch_opt(int opt, const char *arg)
         fprintf(stderr, "Invalid value for VQ (1-%d)\n", SVE_VQ_MAX);
         exit(EXIT_FAILURE);
     }
-    want = sve_vl_from_vq(test_sve);
-    got = prctl(PR_SVE_SET_VL, want);
-    if (want != got) {
-        if (got < 0) {
-            perror("prctl PR_SVE_SET_VL");
-        } else {
-            fprintf(stderr, "Unsupported value for VQ (%d != %d)\n",
-                    test_sve, (int)sve_vq_from_vl(got));
-        }
-        exit(EXIT_FAILURE);
-    }
 #else
     abort();
 #endif
 }
 
+void arch_init(void)
+{
+#ifdef SVE_MAGIC
+    long want, got1, got2;
+
+    if (test_sve == 0) {
+        return;
+    }
+
+    want = sve_vl_from_vq(test_sve);
+    asm(".arch_extension sve\n\trdvl %0, #1" : "=r"(got1));
+    if (want != got1) {
+        got2 = prctl(PR_SVE_SET_VL, want);
+        if (want != got2) {
+            if (got2 < 0) {
+                perror("prctl PR_SVE_SET_VL");
+                got2 = got1;
+            }
+            fprintf(stderr, "Unsupported value for VQ (%d != %d)\n",
+                    test_sve, (int)sve_vq_from_vl(got1));
+            exit(EXIT_FAILURE);
+        }
+    }
+#endif
+}
+
 int reginfo_size(struct reginfo *ri)
 {
 #ifdef SVE_MAGIC
@@ -170,6 +183,7 @@ void reginfo_init(struct reginfo *ri, ucontext_t *uc)
         if (sve->head.size < SVE_SIG_CONTEXT_SIZE(vq)) {
             if (sve->head.size == sizeof(*sve)) {
                 /* SVE state is empty -- not an error.  */
+                goto do_simd;
             } else {
                 fprintf(stderr, "risu_reginfo_aarch64: "
                         "failed to get complete SVE state\n");
@@ -182,6 +196,7 @@ void reginfo_init(struct reginfo *ri, ucontext_t *uc)
                SVE_SIG_CONTEXT_SIZE(vq) - SVE_SIG_REGS_OFFSET);
         return;
     }
+ do_simd:
 #endif /* SVE_MAGIC */
 
     for (i = 0; i < 32; i++) {
@@ -260,8 +275,9 @@ int reginfo_dump(struct reginfo *ri, FILE * f)
     fprintf(f, "  fpcr   : %08x\n", ri->fpcr);
 
 #ifdef SVE_MAGIC
-    if (test_sve) {
-        int q, vq = test_sve;
+    if (ri->sve_vl) {
+        int vq = sve_vq_from_vl(ri->sve_vl);
+        int q;
 
         fprintf(f, "  vl     : %d\n", ri->sve_vl);
 
@@ -339,13 +355,12 @@ int reginfo_dump_mismatch(struct reginfo *m, struct reginfo *a, FILE * f)
     }
 
 #ifdef SVE_MAGIC
-    if (test_sve) {
+    if (m->sve_vl != a->sve_vl) {
+        fprintf(f, "  vl    : %d vs %d\n", m->sve_vl, a->sve_vl);
+    }
+    if (m->sve_vl) {
         int vq = sve_vq_from_vl(m->sve_vl);
 
-        if (m->sve_vl != a->sve_vl) {
-            fprintf(f, "  vl    : %d vs %d\n", m->sve_vl, a->sve_vl);
-        }
-
         for (i = 0; i < SVE_NUM_ZREGS; i++) {
             uint64_t *zm = reginfo_zreg(m, vq, i);
             uint64_t *za = reginfo_zreg(a, vq, i);
diff --git a/risu_reginfo_arm.c b/risu_reginfo_arm.c
index 47c52e8..202120b 100644
--- a/risu_reginfo_arm.c
+++ b/risu_reginfo_arm.c
@@ -36,6 +36,10 @@ void process_arch_opt(int opt, const char *arg)
     abort();
 }
 
+void arch_init(void)
+{
+}
+
 int reginfo_size(struct reginfo *ri)
 {
     return sizeof(*ri);
diff --git a/risu_reginfo_i386.c b/risu_reginfo_i386.c
index 50505ab..e9730be 100644
--- a/risu_reginfo_i386.c
+++ b/risu_reginfo_i386.c
@@ -74,6 +74,10 @@ void process_arch_opt(int opt, const char *arg)
     }
 }
 
+void arch_init(void)
+{
+}
+
 int reginfo_size(struct reginfo *ri)
 {
     return sizeof(*ri);
diff --git a/risu_reginfo_m68k.c b/risu_reginfo_m68k.c
index 4eb30cd..4c25e77 100644
--- a/risu_reginfo_m68k.c
+++ b/risu_reginfo_m68k.c
@@ -23,6 +23,10 @@ void process_arch_opt(int opt, const char *arg)
     abort();
 }
 
+void arch_init(void)
+{
+}
+
 int reginfo_size(struct reginfo *ri)
 {
     return sizeof(*ri);
diff --git a/risu_reginfo_ppc64.c b/risu_reginfo_ppc64.c
index 39e8f1c..c80e387 100644
--- a/risu_reginfo_ppc64.c
+++ b/risu_reginfo_ppc64.c
@@ -32,6 +32,10 @@ void process_arch_opt(int opt, const char *arg)
     abort();
 }
 
+void arch_init(void)
+{
+}
+
 int reginfo_size(struct reginfo *ri)
 {
     return sizeof(*ri);
