From: Helge Deller <deller@gmx.de>

The value of unwind_breg may reference register %r0, but we need to avoid
accessing gr0 directly and use the value 0 instead.

At runtime I've seen unwind_breg being zero with the Linux kernel when
rfi is used to jump to smp_callin().

Signed-off-by: Helge Deller <deller@gmx.de>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Bruno Haible <bruno@clisp.org>
(cherry picked from commit 5915b67013eb8c3a84e3ef05e6ba4eae55ccd173)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/target/hppa/mem_helper.c b/target/hppa/mem_helper.c
index 4c28c58ee9..1387f4a64b 100644
--- a/target/hppa/mem_helper.c
+++ b/target/hppa/mem_helper.c
@@ -341,7 +341,7 @@ raise_exception_with_ior(CPUHPPAState *env, int excp, uintptr_t retaddr,
 
                 cpu_restore_state(cs, retaddr);
 
-                b = env->gr[env->unwind_breg];
+                b = env->unwind_breg ? env->gr[env->unwind_breg] : 0;
                 b >>= (env->psw & PSW_W ? 62 : 30);
                 env->cr[CR_IOR] |= b << 62;
 
-- 
2.39.2