commit 7055fe4baf4d8b331863e51a15e93d3bdea29e36
author Richard Henderson <richard.henderson@linaro.org> Wed Nov 03 00:03:50 2021 -0400
committer Peter Maydell <peter.maydell@linaro.org> Wed Dec 15 10:35:26 2021 +0000
tree dffae3f23b9b544e17ff2edc57b50d7d6b527376
parent ee03027a2cef00f977a3d28242c0a250b8552495

target/arm: Assert thumb pc is aligned

Misaligned thumb PC is architecturally impossible.
Assert is better than proceeding, in case we've missed
something somewhere.

Expand a comment about aligning the pc in gdbstub.
Fail an incoming migrate if a thumb pc is misaligned.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/gdbstub.c

diff --git a/target/arm/gdbstub.c b/target/arm/gdbstub.c
index 134da0d..ca1de47 100644
--- a/target/arm/gdbstub.c
+++ b/target/arm/gdbstub.c
@@ -77,8 +77,13 @@
 
     tmp = ldl_p(mem_buf);
 
-    /* Mask out low bit of PC to workaround gdb bugs.  This will probably
-       cause problems if we ever implement the Jazelle DBX extensions.  */
+    /*
+     * Mask out low bits of PC to workaround gdb bugs.
+     * This avoids an assert in thumb_tr_translate_insn, because it is
+     * architecturally impossible to misalign the pc.
+     * This will probably cause problems if we ever implement the
+     * Jazelle DBX extensions.
+     */
     if (n == 15) {
         tmp &= ~1;
     }

target/arm/machine.c

diff --git a/target/arm/machine.c b/target/arm/machine.c
index c74d8c3..135d242 100644
--- a/target/arm/machine.c
+++ b/target/arm/machine.c
@@ -794,6 +794,16 @@
             return -1;
         }
     }
+
+    /*
+     * Misaligned thumb pc is architecturally impossible.
+     * We have an assert in thumb_tr_translate_insn to verify this.
+     * Fail an incoming migrate to avoid this assert.
+     */
+    if (!is_a64(env) && env->thumb && (env->regs[15] & 1)) {
+        return -1;
+    }
+
     if (!kvm_enabled()) {
         pmu_op_finish(&cpu->env);
     }

target/arm/translate.c

diff --git a/target/arm/translate.c b/target/arm/translate.c
index 45917c3..0a3840d 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -9646,6 +9646,9 @@
     uint32_t insn;
     bool is_16bit;
 
+    /* Misaligned thumb PC is architecturally impossible. */
+    assert((dc->base.pc_next & 1) == 0);
+
     if (arm_check_ss_active(dc) || arm_check_kernelpage(dc)) {
         dc->base.pc_next = pc + 2;
         return;