Fix issue #15778: GDB Aarch64 signal frame unwinder issue

The root cause of this issue is unwinder of "#3  <signal handler called>"
doesn't supply right values of registers.
When GDB want to get the previous frame of "#3  <signal handler called>",
it will call cache init function of unwinder "aarch64_linux_sigframe_init".
The address or the value of the registers is get from this function.
So the bug is inside thie function.

I check the asm code of "#3  <signal handler called>":
(gdb) frame 3
(gdb) p $pc
$1 = (void (*)()) 0x7f931fa4d0
(gdb) disassemble $pc, +10
Dump of assembler code from 0x7f931fa4d0 to 0x7f931fa4da:
=> 0x0000007f931fa4d0:	mov	x8, #0x8b                  	// #139
   0x0000007f931fa4d4:	svc	#0x0
   0x0000007f931fa4d8:	nop

This is the syscall sys_rt_sigreturn, Linux kernel function "restore_sigframe"
will set the frame:
	for (i = 0; i < 31; i++)
		__get_user_error(regs->regs[i], &sf->uc.uc_mcontext.regs[i],
				 err);
	__get_user_error(regs->sp, &sf->uc.uc_mcontext.sp, err);
	__get_user_error(regs->pc, &sf->uc.uc_mcontext.pc, err);
The struct of uc_mcontext is:
struct sigcontext {
	__u64 fault_address;
	/* AArch64 registers */
	__u64 regs[31];
	__u64 sp;
	__u64 pc;
	__u64 pstate;
	/* 4K reserved for FP/SIMD state and future expansion */
	__u8 __reserved[4096] __attribute__((__aligned__(16)));
};

But in GDB function "aarch64_linux_sigframe_init", the code the get address
of registers is:
  for (i = 0; i < 31; i++)
    {
      trad_frame_set_reg_addr (this_cache,
			       AARCH64_X0_REGNUM + i,
			       sigcontext_addr + AARCH64_SIGCONTEXT_XO_OFFSET
			       + i * AARCH64_SIGCONTEXT_REG_SIZE);
    }

  trad_frame_set_reg_addr (this_cache, AARCH64_FP_REGNUM, fp);
  trad_frame_set_reg_addr (this_cache, AARCH64_LR_REGNUM, fp + 8);
  trad_frame_set_reg_addr (this_cache, AARCH64_PC_REGNUM, fp + 8);

The code that get pc and sp is not right, so I change the code according
to Linux kernel code:
  trad_frame_set_reg_addr (this_cache, AARCH64_SP_REGNUM,
			   sigcontext_addr + AARCH64_SIGCONTEXT_XO_OFFSET
			     + 31 * AARCH64_SIGCONTEXT_REG_SIZE);
  trad_frame_set_reg_addr (this_cache, AARCH64_PC_REGNUM,
			   sigcontext_addr + AARCH64_SIGCONTEXT_XO_OFFSET
			     + 32 * AARCH64_SIGCONTEXT_REG_SIZE);

The issue was fixed by this change, and I did the regression test.  It
also fixed a lot of other XFAIL and FAIL.

2014-05-20  Hui Zhu  <hui@codesourcery.com>
	    Yao Qi  <yao@codesourcery.com>

	PR backtrace/16558
	* aarch64-linux-tdep.c (aarch64_linux_sigframe_init): Update comments
	and change address of sp and pc.

2 files changed, 41 insertions, 29 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 394f1ed..22ca25c8 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,10 @@
+2014-05-20  Hui Zhu  <hui@codesourcery.com>
+	    Yao Qi  <yao@codesourcery.com>
+
+	PR backtrace/16558
+	* aarch64-linux-tdep.c (aarch64_linux_sigframe_init): Update comments
+	and change address of sp and pc.
+
 2014-05-19  Tom Tromey  <tromey@redhat.com>
 
 	* gdbtypes.c (rank_function): Use XNEWVEC.
diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
index 92d1248..a89bf32 100644
--- a/gdb/aarch64-linux-tdep.c
+++ b/gdb/aarch64-linux-tdep.c
@@ -53,28 +53,30 @@
 
 /* Signal frame handling.
 
-      +----------+  ^
-      | saved lr |  |
-   +->| saved fp |--+
-   |  |          |
-   |  |          |
-   |  +----------+
-   |  | saved lr |
-   +--| saved fp |
-   ^  |          |
-   |  |          |
-   |  +----------+
-   ^  |          |
-   |  | signal   |
-   |  |          |
-   |  | saved lr |-->interrupted_function_pc
-   +--| saved fp |
-   |  +----------+
-   |  | saved lr |--> default_restorer (movz x8, NR_sys_rt_sigreturn; svc 0)
-   +--| saved fp |<- FP
-      |          |
-      |          |<- SP
-      +----------+
+      +------------+  ^
+      | saved lr   |  |
+   +->| saved fp   |--+
+   |  |            |
+   |  |            |
+   |  +------------+
+   |  | saved lr   |
+   +--| saved fp   |
+   ^  |            |
+   |  |            |
+   |  +------------+
+   ^  |            |
+   |  | signal     |
+   |  |            |        SIGTRAMP_FRAME (struct rt_sigframe)
+   |  | saved regs |
+   +--| saved sp   |--> interrupted_sp
+   |  | saved pc   |--> interrupted_pc
+   |  |            |
+   |  +------------+
+   |  | saved lr   |--> default_restorer (movz x8, NR_sys_rt_sigreturn; svc 0)
+   +--| saved fp   |<- FP
+      |            |         NORMAL_FRAME
+      |            |<- SP
+      +------------+
 
   On signal delivery, the kernel will create a signal handler stack
   frame and setup the return address in LR to point at restorer stub.
@@ -123,6 +125,8 @@
   d28015a8        movz    x8, #0xad
   d4000001        svc     #0x0
 
+  This is a system call sys_rt_sigreturn.
+
   We detect signal frames by snooping the return code for the restorer
   instruction sequence.
 
@@ -146,7 +150,6 @@ aarch64_linux_sigframe_init (const struct tramp_frame *self,
 {
   struct gdbarch *gdbarch = get_frame_arch (this_frame);
   CORE_ADDR sp = get_frame_register_unsigned (this_frame, AARCH64_SP_REGNUM);
-  CORE_ADDR fp = get_frame_register_unsigned (this_frame, AARCH64_FP_REGNUM);
   CORE_ADDR sigcontext_addr =
     sp
     + AARCH64_RT_SIGFRAME_UCONTEXT_OFFSET
@@ -160,12 +163,14 @@ aarch64_linux_sigframe_init (const struct tramp_frame *self,
 			       sigcontext_addr + AARCH64_SIGCONTEXT_XO_OFFSET
 			       + i * AARCH64_SIGCONTEXT_REG_SIZE);
     }
-
-  trad_frame_set_reg_addr (this_cache, AARCH64_FP_REGNUM, fp);
-  trad_frame_set_reg_addr (this_cache, AARCH64_LR_REGNUM, fp + 8);
-  trad_frame_set_reg_addr (this_cache, AARCH64_PC_REGNUM, fp + 8);
-
-  trad_frame_set_id (this_cache, frame_id_build (fp, func));
+  trad_frame_set_reg_addr (this_cache, AARCH64_SP_REGNUM,
+			   sigcontext_addr + AARCH64_SIGCONTEXT_XO_OFFSET
+			     + 31 * AARCH64_SIGCONTEXT_REG_SIZE);
+  trad_frame_set_reg_addr (this_cache, AARCH64_PC_REGNUM,
+			   sigcontext_addr + AARCH64_SIGCONTEXT_XO_OFFSET
+			     + 32 * AARCH64_SIGCONTEXT_REG_SIZE);
+
+  trad_frame_set_id (this_cache, frame_id_build (sp, func));
 }
 
 static const struct tramp_frame aarch64_linux_rt_sigframe =