Re: [Patch,ARM] Next pc of sigreturn/rt_sigreturn syscall

[Yao Qi <yao@codesourcery.com>]

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Daniel Jacobowitz wrote:
> Generally looks OK.
> 
> On Tue, Aug 24, 2010 at 08:05:55PM -0700, Yao Qi wrote:
>> Here is the updated patch, in which:
>>   1.  Add arm_linux_syscall_next_pc, similar to
>> mips_linux_syscall_next_pc.  Compute the return address of SWI in both
>> ARM mode and Thumb mode.
>>   2.  Extract some common code from arm_linux_copy_svc.
> 
> A valid return address won't be zero, but it's still confusing.
> Please do this the way that e.g. mips_linux_get_longjmp_target does;
> return 0 or 1, and have a CORE_ADDR * parameter.
> 
OK, done as you suggested.

>> +static int
>> +arm_linux_sigreturn_return_addr(struct frame_info *frame,
>> +				unsigned long svc_number)
> 
> Space before "(".  Same problem in other places, too.
> 

Done.

>> +/* When FRAME is at a syscall instruction, return the PC of the next
>> +   instruction to be executed.  */
>> +
>> +static CORE_ADDR
>> +arm_linux_syscall_next_pc (struct frame_info *frame)
>> +{
>> +  CORE_ADDR pc = get_frame_pc (frame);
>> +  CORE_ADDR return_addr = 0;
>> +  return_addr = arm_linux_sigreturn_return_addr(frame,
>> +						get_frame_register_unsigned (frame, 7));
> 
> Line too long; move the read of r7 to another temporary.
> 

Done.

> What about non-EABI?  We shouldn't wire this up for non-EABI binaries,
> because the syscall number won't be in r7.

I've added code for non-EABI to decode SWI instruction for syscall
number.  See details in my patch.

> 
>> @@ -2808,7 +2808,16 @@ thumb_get_next_pc_raw (struct frame_info *frame, CORE_ADDR pc, int insert_bkpt)
>>    else if ((inst1 & 0xf000) == 0xd000)	/* conditional branch */
>>      {
>>        unsigned long cond = bits (inst1, 8, 11);
>> -      if (cond != 0x0f && condition_true (cond, status))    /* 0x0f = SWI */
>> +      if (cond == 0x0f)  /* 0x0f = SWI */
> 
> Why did you remove the condition_true check?

Because I noticed that condition_true always returns true if cond is 0xf
(INST_NV).

>> +	{
>> +	  struct gdbarch_tdep *tdep;
>> +	  tdep = gdbarch_tdep (get_frame_arch (frame));
> 
> You can just use gdbarch_tdep (gdbarch).

OK, done in my patch.

-- 
Yao Qi
CodeSourcery
yao@codesourcery.com
(650) 331-3385 x739

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2010-08-26  Yao Qi  <yao@codesourcery.com>

	* arm-linux-tdep.c (arm_linux_sigreturn_return_addr): New.
	(arm_linux_syscall_next_pc): New.
	(arm_linux_copy_svc): Use arm_linux_sigreturn_return_addr instead. 
	(arm_linux_init_abi): Initialize syscall_next_pc.
	* arm-tdep.c (thumb_get_next_pc_raw):  Get next pc of SWI in Thumb mode.
	(arm_get_next_pc_raw): Get next pc of SWI in ARM mode.
	* arm-tdep.h (struct gdbarch_tdep): Add a function pointer syscall_next_pc. 
	Declare arm_frame_is_thumb.

diff --git a/gdb/arm-linux-tdep.c b/gdb/arm-linux-tdep.c
index 682054c..f0e1dfa 100644
--- a/gdb/arm-linux-tdep.c
+++ b/gdb/arm-linux-tdep.c
@@ -630,6 +630,82 @@ arm_linux_regset_from_core_section (struct gdbarch *gdbarch,
   return NULL;
 }
 
+/* Copy the value of next pc of sigreturn and rt_sigrturn into PC,
+   and return 1.  Return 0 if it is not a rt_sigreturn/sigreturn
+   syscall.  */
+static int
+arm_linux_sigreturn_return_addr (struct frame_info *frame,
+				 unsigned long svc_number,
+				 CORE_ADDR *pc)
+{
+  /* Is this a sigreturn or rt_sigreturn syscall?  */
+  if (svc_number == 119 || svc_number == 173)
+    {
+      if (get_frame_type (frame) == SIGTRAMP_FRAME)
+	{
+	  *pc = frame_unwind_caller_pc (frame);
+	  return 1;
+	}
+    }
+  return 0;
+}
+
+/* When FRAME is at a syscall instruction, return the PC of the next
+   instruction to be executed.  */
+
+static CORE_ADDR
+arm_linux_syscall_next_pc (struct frame_info *frame)
+{
+  CORE_ADDR pc = get_frame_pc (frame);
+  CORE_ADDR return_addr = 0;
+  int is_thumb = arm_frame_is_thumb (frame);
+  ULONGEST svc_number = 0;
+  int is_sigreturn = 0;
+
+  if (is_thumb)
+    {
+      svc_number = get_frame_register_unsigned (frame, 7);
+    }
+  else
+    {
+      struct gdbarch *gdbarch = get_frame_arch (frame);
+      enum bfd_endian byte_order_for_code = 
+	gdbarch_byte_order_for_code (gdbarch);
+      unsigned long this_instr = 
+	read_memory_unsigned_integer (pc, 4, byte_order_for_code);
+
+      unsigned long svc_operand = (0x00ffffff & this_instr);
+      if (svc_operand)  /* OABI.  */
+	{
+	  svc_number = svc_operand - 0x900000;
+	}
+      else /* EABI.  */
+	{
+	  svc_number = get_frame_register_unsigned (frame, 7);
+	}
+    }
+
+  is_sigreturn = arm_linux_sigreturn_return_addr (frame, svc_number, 
+						  &return_addr);
+
+  if (is_sigreturn)
+    return return_addr;
+  
+  if (is_thumb)
+    {
+      return_addr = pc + 2;
+      /* Addresses for calling Thumb functions have the bit 0 set.  */
+      return_addr |= 1;
+    }
+  else
+    {
+      return_addr = pc + 4;
+    }
+
+  return return_addr;
+}
+
+
 /* Insert a single step breakpoint at the next executed instruction.  */
 
 static int
@@ -688,8 +764,11 @@ arm_linux_copy_svc (struct gdbarch *gdbarch, uint32_t insn, CORE_ADDR to,
 		    struct regcache *regs, struct displaced_step_closure *dsc)
 {
   CORE_ADDR from = dsc->insn_addr;
+  CORE_ADDR return_to = 0;
+
   struct frame_info *frame;
   unsigned int svc_number = displaced_read_reg (regs, from, 7);
+  int is_sigreturn = 0;
 
   if (debug_displaced)
     fprintf_unfiltered (gdb_stdlog, "displaced: copying Linux svc insn %.8lx\n",
@@ -697,13 +776,10 @@ arm_linux_copy_svc (struct gdbarch *gdbarch, uint32_t insn, CORE_ADDR to,
 
   frame = get_current_frame ();
 
-  /* Is this a sigreturn or rt_sigreturn syscall?  Note: these are only useful
-     for EABI.  */
-  if (svc_number == 119 || svc_number == 173)
+  is_sigreturn = arm_linux_sigreturn_return_addr(frame, svc_number,
+						 &return_to);
+  if (is_sigreturn)
     {
-      if (get_frame_type (frame) == SIGTRAMP_FRAME)
-	{
-	  CORE_ADDR return_to;
 	  struct symtab_and_line sal;
 
 	  if (debug_displaced)
@@ -711,7 +787,6 @@ arm_linux_copy_svc (struct gdbarch *gdbarch, uint32_t insn, CORE_ADDR to,
 	      "sigreturn/rt_sigreturn SVC call. PC in frame = %lx\n",
 	      (unsigned long) get_frame_pc (frame));
 
-	  return_to = frame_unwind_caller_pc (frame);
 	  if (debug_displaced)
 	    fprintf_unfiltered (gdb_stdlog, "displaced: unwind pc = %lx. "
 	      "Setting momentary breakpoint.\n", (unsigned long) return_to);
@@ -743,7 +818,7 @@ arm_linux_copy_svc (struct gdbarch *gdbarch, uint32_t insn, CORE_ADDR to,
       else if (debug_displaced)
 	fprintf_unfiltered (gdb_stdlog, "displaced: sigreturn/rt_sigreturn "
 			    "SVC call not in signal trampoline frame\n");
-    }
+    
 
   /* Preparation: If we detect sigreturn, set momentary breakpoint at resume
 		  location, else nothing.
@@ -946,6 +1021,9 @@ arm_linux_init_abi (struct gdbarch_info info,
   set_gdbarch_displaced_step_free_closure (gdbarch,
 					   simple_displaced_step_free_closure);
   set_gdbarch_displaced_step_location (gdbarch, displaced_step_at_entry_point);
+
+
+  tdep->syscall_next_pc = arm_linux_syscall_next_pc;
 }
 
 /* Provide a prototype to silence -Wmissing-prototypes.  */
diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
index 1ac8817..36b46b5 100644
--- a/gdb/arm-tdep.c
+++ b/gdb/arm-tdep.c
@@ -257,7 +257,7 @@ int arm_apcs_32 = 1;
 
 /* Determine if FRAME is executing in Thumb mode.  */
 
-static int
+int
 arm_frame_is_thumb (struct frame_info *frame)
 {
   CORE_ADDR cpsr;
@@ -2808,7 +2808,16 @@ thumb_get_next_pc_raw (struct frame_info *frame, CORE_ADDR pc, int insert_bkpt)
   else if ((inst1 & 0xf000) == 0xd000)	/* conditional branch */
     {
       unsigned long cond = bits (inst1, 8, 11);
-      if (cond != 0x0f && condition_true (cond, status))    /* 0x0f = SWI */
+      if (cond == 0x0f)  /* 0x0f = SWI */
+	{
+	  struct gdbarch_tdep *tdep;
+	  tdep = gdbarch_tdep (gdbarch);
+
+	  if (tdep->syscall_next_pc != NULL)
+	    nextpc = tdep->syscall_next_pc (frame);
+
+	}
+      else if (cond != 0x0f && condition_true (cond, status))
 	nextpc = pc_val + (sbits (inst1, 0, 7) << 1);
     }
   else if ((inst1 & 0xf800) == 0xe000)	/* unconditional branch */
@@ -3257,7 +3266,16 @@ arm_get_next_pc_raw (struct frame_info *frame, CORE_ADDR pc, int insert_bkpt)
 	case 0xc:
 	case 0xd:
 	case 0xe:		/* coproc ops */
+	  break;
 	case 0xf:		/* SWI */
+	  {
+	    struct gdbarch_tdep *tdep;
+	    tdep = gdbarch_tdep (gdbarch);
+
+	    if (tdep->syscall_next_pc != NULL)
+	      nextpc = tdep->syscall_next_pc (frame);
+
+	  }
 	  break;
 
 	default:
diff --git a/gdb/arm-tdep.h b/gdb/arm-tdep.h
index b6283ef..2f4e99b 100644
--- a/gdb/arm-tdep.h
+++ b/gdb/arm-tdep.h
@@ -193,6 +193,10 @@ struct gdbarch_tdep
   struct type *arm_ext_type;
   struct type *neon_double_type;
   struct type *neon_quad_type;
+
+  /* Return the expected next PC if FRAME is stopped at a syscall
+     instruction.  */
+  CORE_ADDR (*syscall_next_pc) (struct frame_info *frame);
 };
 
 /* Structures used for displaced stepping.  */
@@ -294,6 +298,7 @@ extern void
 CORE_ADDR arm_skip_stub (struct frame_info *, CORE_ADDR);
 CORE_ADDR arm_get_next_pc (struct frame_info *, CORE_ADDR);
 int arm_software_single_step (struct frame_info *);
+int arm_frame_is_thumb (struct frame_info *frame);
 
 extern struct displaced_step_closure *
   arm_displaced_step_copy_insn (struct gdbarch *, CORE_ADDR, CORE_ADDR,