[Qemu-devel] [PATCH v6 1/6] linux-user/aarch64: Reset btype for syscalls and signals

[Richard Henderson <richard.henderson@linaro.org>]

The value of btype for syscalls is CONSTRAINED UNPREDICTABLE,
so we need to make sure that the value is 0 before clone,
fork, or syscall return.

The kernel sets btype for the signal handler as if for a call.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 linux-user/aarch64/cpu_loop.c |  7 +++++++
 linux-user/aarch64/signal.c   | 10 ++++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/linux-user/aarch64/cpu_loop.c b/linux-user/aarch64/cpu_loop.c
index 2f2f63e3e8..1f68b13168 100644
--- a/linux-user/aarch64/cpu_loop.c
+++ b/linux-user/aarch64/cpu_loop.c
@@ -86,6 +86,13 @@ void cpu_loop(CPUARMState *env)
 
         switch (trapnr) {
         case EXCP_SWI:
+            /*
+             * The state of BTYPE on syscall entry is CONSTRAINED
+             * UNPREDICTABLE.  The real kernel will need to tidy this up
+             * as well.  Do this before syscalls so that the value is
+             * correct on return from syscall (especially clone & fork).
+             */
+            env->btype = 0;
             ret = do_syscall(env,
                              env->xregs[8],
                              env->xregs[0],
diff --git a/linux-user/aarch64/signal.c b/linux-user/aarch64/signal.c
index f84a9cf28a..5605d404b3 100644
--- a/linux-user/aarch64/signal.c
+++ b/linux-user/aarch64/signal.c
@@ -506,10 +506,16 @@ static void target_setup_frame(int usig, struct target_sigaction *ka,
             + offsetof(struct target_rt_frame_record, tramp);
     }
     env->xregs[0] = usig;
-    env->xregs[31] = frame_addr;
     env->xregs[29] = frame_addr + fr_ofs;
-    env->pc = ka->_sa_handler;
     env->xregs[30] = return_addr;
+    env->xregs[31] = frame_addr;
+    env->pc = ka->_sa_handler;
+
+    /* Invoke the signal handler as if by indirect call.  */
+    if (cpu_isar_feature(aa64_bti, arm_env_get_cpu(env))) {
+        env->btype = 2;
+    }
+
     if (info) {
         tswap_siginfo(&frame->info, info);
         env->xregs[1] = frame_addr + offsetof(struct target_rt_sigframe, info);
-- 
2.17.1