[Qemu-devel] [PATCH v4 1/4] linux-user/aarch64: Reset btype for syscalls and signals

[Richard Henderson]

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 value of btype for signals is defined, but it does not make
sense for a SIGILL handler to enter with the btype set as for
the indirect branch that caused the SIGILL.

Signed-off-by: Richard Henderson <address@hidden>
---
v4: Do not clear btype in signal frame.
---
 linux-user/aarch64/cpu_loop.c | 7 +++++++
 linux-user/aarch64/signal.c   | 5 +++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/linux-user/aarch64/cpu_loop.c b/linux-user/aarch64/cpu_loop.c
index d75fd9d3e2..f5cce4769d 100644
--- a/linux-user/aarch64/cpu_loop.c
+++ b/linux-user/aarch64/cpu_loop.c
@@ -85,6 +85,13 @@ 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..078873c4a5 100644
--- a/linux-user/aarch64/signal.c
+++ b/linux-user/aarch64/signal.c
@@ -506,10 +506,11 @@ 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;
+    env->btype = 0;
     if (info) {
         tswap_siginfo(&frame->info, info);
         env->xregs[1] = frame_addr + offsetof(struct target_rt_sigframe, info);
-- 
2.17.1