Prevent traps after rsp modification

gdb/nacl-tdep.c

Index: gdb/nacl-tdep.c
diff --git a/gdb/nacl-tdep.c b/gdb/nacl-tdep.c
index 53dc8f9f253bc94ca38354b33b667f8b8441cf6c..6ac49c75b7078453736102c85a2c855b0b71cf66 100644
--- a/gdb/nacl-tdep.c
+++ b/gdb/nacl-tdep.c
@@ -27,6 +27,9 @@
 #include "solib-svr4.h"
 #include "frame.h"
 #include "osabi.h"
+#include "disasm.h"
+#include "breakpoint.h"
+#include "target.h"
 
 static void
 nacl_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
@@ -99,6 +102,52 @@ amd64_nacl_fetch_link_map_offsets (void)
   return lmp;
 }
 
+static CORE_ADDR
+amd64_nacl_skip_rsp_sandboxing (CORE_ADDR addr)
+{
+  gdb_byte buf[3];
+  if (target_read_memory (addr, buf, sizeof(buf)) == 0)
+    {
+      /* 4c 01 fc    add  %r15,%rsp  */
+      if (buf[0] == 0x4c && buf[1] == 0x01 && buf[2] == 0xfc)
+        {
+          return addr + 3;
+        }
+    }
+  return addr;
+}
+
+static CORE_ADDR
+amd64_nacl_adjust_breakpoint_address (struct gdbarch *gdbarch, CORE_ADDR addr)
+{
+  return amd64_nacl_skip_rsp_sandboxing (addr);
+}
+
+static int
+amd64_nacl_software_single_step (struct frame_info *frame)
+{
+  struct gdbarch *gdbarch;
+  CORE_ADDR pc;
+  CORE_ADDR bp_pc;
+
+  gdbarch = get_frame_arch (frame);
+  pc = get_frame_register_unsigned (frame, gdbarch_pc_regnum (gdbarch));
+
+  /* Check if next instruction is rsp sandboxing.  If yes, assume current
+     instruction is rsp modification.  */
+  pc += gdb_insn_length (gdbarch, pc);
+  bp_pc = amd64_nacl_skip_rsp_sandboxing (pc);
+  if (bp_pc != pc)
+    {
+      insert_single_step_breakpoint (gdbarch,
+                                     get_frame_address_space (frame),
+                                     bp_pc);
+      return 1;
+    }
+
+  return 0;
+}
+
 static void
 amd64_nacl_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
 {
@@ -130,6 +179,11 @@ amd64_nacl_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
   set_gdbarch_addr_bits_remove (gdbarch, amd64_nacl_addr_bits_remove);
   set_gdbarch_unwind_pc (gdbarch, amd64_nacl_unwind_pc);
   set_gdbarch_unwind_sp (gdbarch, amd64_nacl_unwind_sp);
+
+  /* Where to set breakpoints.  */
+  set_gdbarch_adjust_breakpoint_address (gdbarch,
+                                         amd64_nacl_adjust_breakpoint_address);
+  set_gdbarch_software_single_step (gdbarch, amd64_nacl_software_single_step);
 }
 
 /* Provide a prototype to silence -Wmissing-prototypes.  */