feature/android 6a30a74cb2a 1/3: Fix syscall error reporting on aarch64

[Po Lu]

branch: feature/android
commit 6a30a74cb2ac2cba69aa01da12caf1eac7134f43
Author: Po Lu <luangruo@yahoo.com>
Commit: Po Lu <luangruo@yahoo.com>

    Fix syscall error reporting on aarch64
    
    * exec/trace.c (process_system_call): Save and restore x0, x1
    and x2 regs after replacing them with an invalid file
    descriptor.
---
 exec/trace.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/exec/trace.c b/exec/trace.c
index cef699e8526..df5deacd9bb 100644
--- a/exec/trace.c
+++ b/exec/trace.c
@@ -627,6 +627,9 @@ process_system_call (struct exec_tracee *tracee)
   USER_REGS_STRUCT regs;
   int rc, wstatus;
   USER_WORD callno, sp;
+#ifdef __aarch64__
+  USER_WORD old_w0, old_w1, old_w2;
+#endif /* __aarch64__ */
 
 #ifdef __aarch64__
   rc = aarch64_get_regs (tracee->pid, &regs);
@@ -692,7 +695,20 @@ process_system_call (struct exec_tracee *tracee)
      Make sure that the stack pointer is restored to its original
      position upon exit, or bad things can happen.  */
 
+#ifndef __aarch64__
   regs.SYSCALL_NUM_REG = -1;
+#else /* __aarch64__ */
+  /* ARM also requires the system call number to be valid.  However, I
+     can't find any unused system call, so use fcntl instead, with
+     invalid arguments.  */
+  regs.SYSCALL_NUM_REG = 72;
+  old_w0 = regs.regs[0];
+  old_w1 = regs.regs[1];
+  old_w2 = regs.regs[2];
+  regs.regs[0] = -1;
+  regs.regs[1] = -1;
+  regs.regs[2] = -1;
+#endif /* !__aarch64__ */
   regs.STACK_POINTER   = sp;
 
 #ifdef __aarch64__
@@ -714,7 +730,6 @@ process_system_call (struct exec_tracee *tracee)
     return;
 #endif /* __aarch64__ */
 
-
   /* Do this invalid system call.  */
   if (ptrace (PTRACE_SYSCALL, tracee->pid, NULL, NULL))
     return;
@@ -740,6 +755,10 @@ process_system_call (struct exec_tracee *tracee)
 
       /* Report errno.  */
 #ifdef __aarch64__
+      /* Restore x0, x1 and x2.  */
+      regs.regs[0] = old_w0;
+      regs.regs[1] = old_w1;
+      regs.regs[2] = old_w2;
       aarch64_set_regs (tracee->pid, &regs, false);
 #else /* !__aarch64__ */
       ptrace (PTRACE_SETREGS, tracee->pid, NULL, &regs);