[AArch64][4/6] Prologue scan unwinder support for signed return address

[Jiong Wang <jiong dot wang at foss dot arm dot com>]

This patch add prologue scan unwinder support for signed (mangled) return
address on AArch64.

aarch64_analyze_prologue is taught about the new "paciasp" and "autiasp"
instructions which are used to sign and authenticate return address.  Prologue
scan unwinder scan their existence to record the signing status of return
address in "ra_state" register which will be used in register unwind method to
restore original value of return address.
                                                                         
I have checked "autiasp" in prologue scanner although it is supposed to be in
epilogue only if the debuggee is compiled from GCC.

gdb/
2017-08-09  Jiong Wang<jiong.wang@arm.com>

	* aarch64-tdep.c (aarch64_analyze_prologue): Recognize "paciasp"
	and "autiasp".  Record signing status of return address in
	"ra_state".
	(aarch64_prologue_prev_register): Mask off signature from return
	address if it's signed.
	(aarch64_analyze_prologue_test): Add new unit test for return
	address signing instruction.

commit 221194ec9eaa7113ff90632adbb68e0881f07467
Author: Jiong Wang <jiong.wang@arm.com>
Date:   Fri Aug 4 17:14:15 2017 +0100

    [Patch 4]

diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
index b505013..5f7a5a2 100644
--- a/gdb/aarch64-tdep.c
+++ b/gdb/aarch64-tdep.c
@@ -453,6 +453,40 @@ aarch64_analyze_prologue (struct gdbarch *gdbarch,
 	  /* Stop analysis on branch.  */
 	  break;
 	}
+      else if (inst.opcode->iclass == ic_system)
+	{
+	  struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
+	  /* Record the state of return address.
+	     1 means it is mangled, otherwise 0.  */
+	  int ra_state_val = 0;
+
+	  /* PACIASP (HINT 25).
+	     we can't match the name because PACIASP is an alias of HINT while
+	     we are passing a TRUE noaliases_p to aarch64_decode_insn.  */
+	  if (insn == 0xd503233f)
+	    ra_state_val = 1;
+	  /* AUTIASP (HINT 29).  */
+	  else if (insn == 0xd50323bf)
+	    ra_state_val = 0;
+	  else
+	    {
+	      if (aarch64_debug)
+		{
+		  debug_printf ("aarch64: prologue analysis gave up addr=%s"
+				" opcode=0x%x\n",
+				core_addr_to_string_nz (start), insn);
+		}
+	      break;
+	    }
+
+	  if (aarch64_tdep_has_pauth_p (tdep) && cache != NULL)
+	    {
+	      int ra_state = (tdep->regnum.pauth_ra_state_regnum
+			      + gdbarch_num_regs (gdbarch));
+
+	      trad_frame_set_value (cache->saved_regs, ra_state, ra_state_val);
+	    }
+	}
       else
 	{
 	  if (aarch64_debug)
@@ -644,6 +678,58 @@ aarch64_analyze_prologue_test (void)
 		      == -1);
       }
   }
+
+  /* Test a prologue in which there is return address signing instruction.  */
+  {
+    struct aarch64_prologue_cache cache;
+    cache.saved_regs = trad_frame_alloc_saved_regs (gdbarch);
+
+    struct gdbarch_info info;
+
+    gdbarch_info_init (&info);
+    info.bfd_arch_info = bfd_scan_arch ("aarch64");
+    info.target_desc = tdesc_aarch64_pauth;
+
+    struct gdbarch *gdbarch = gdbarch_find_by_info (info);
+    SELF_CHECK (gdbarch != NULL);
+
+    int ra_state = (gdbarch_tdep (gdbarch)->regnum.pauth_ra_state_regnum
+		    + gdbarch_num_regs (gdbarch));
+
+    static const uint32_t insns[] = {
+      0xd503233f, /* paciasp (hint 25) */
+      0xa9bd7bfd, /* stp	x29, x30, [sp, #-48]! */
+      0x910003fd, /* mov	x29, sp */
+      0xf801c3f3, /* str	x19, [sp, #28] */
+      0xb9401fa0, /* ldr	x19, [x29, #28] */
+    };
+    instruction_reader_test reader (insns);
+
+    CORE_ADDR end = aarch64_analyze_prologue (gdbarch, 0, 128, &cache, reader);
+
+    SELF_CHECK (end == 4 * 4);
+
+    SELF_CHECK (cache.framereg == AARCH64_FP_REGNUM);
+    SELF_CHECK (cache.framesize == 48);
+
+    for (int i = 0; i < AARCH64_X_REGISTER_COUNT; i++)
+      {
+	if (i == 19)
+	  SELF_CHECK (cache.saved_regs[i].addr == -20);
+	else if (i == AARCH64_FP_REGNUM)
+	  SELF_CHECK (cache.saved_regs[i].addr == -48);
+	else if (i == AARCH64_LR_REGNUM)
+	  SELF_CHECK (cache.saved_regs[i].addr == -40);
+	else
+	  SELF_CHECK (cache.saved_regs[i].addr == -1);
+      }
+
+    if (aarch64_tdep_has_pauth_p (gdbarch_tdep (gdbarch)))
+      {
+	SELF_CHECK (trad_frame_value_p (cache.saved_regs, ra_state));
+	SELF_CHECK (cache.saved_regs[ra_state].addr == 1);
+      }
+  }
 }
 } // namespace selftests
 #endif /* GDB_SELF_TEST */
@@ -853,8 +939,30 @@ aarch64_prologue_prev_register (struct frame_info *this_frame,
   if (prev_regnum == AARCH64_PC_REGNUM)
     {
       CORE_ADDR lr;
+      struct gdbarch *gdbarch = get_frame_arch (this_frame);
+      struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
 
       lr = frame_unwind_register_unsigned (this_frame, AARCH64_LR_REGNUM);
+
+      if (aarch64_tdep_has_pauth_p (tdep))
+	{
+	  int ra_state_regno = (tdep->regnum.pauth_ra_state_regnum
+				+ gdbarch_num_regs (gdbarch));
+	  if (trad_frame_value_p (cache->saved_regs, ra_state_regno))
+	    {
+	      CORE_ADDR ra_state
+		= frame_unwind_register_unsigned (this_frame, ra_state_regno);
+
+	      if (ra_state)
+		{
+		  int cmask_num = tdep->regnum.pauth_reg_base + 1;
+		  CORE_ADDR cmask
+		    = frame_unwind_register_unsigned (this_frame, cmask_num);
+		  lr = lr & ~cmask;
+		}
+	    }
+	}
+
       return frame_unwind_got_constant (this_frame, prev_regnum, lr);
     }