[PATCH] Fix passing/returning of complex data for PowerPC 32-bit

[Luis Machado <lgustavo at codesourcery dot com>]

The PowerPC 32-bit unified ABI states that there are two ways of passing 
and returning complex type data:

- Pointer, in a register, to a memory area.
- Data in registers.

The problem is that it is not clear how to detect which variation a 
program is using. GDB currently does a bit of both. It uses the first 
mechanism for passing parameters and uses both to return data, depending 
on the size of the data type. It is a bit messy because GDB is not 
handling complex types explicitly.

Checking the gdb.base/callfuncs.exp testcase for a PowerPC 32-bit 
target, with code built with GCC, showed a few failures related to 
complex types.

This patch steers GDB towards what GCC seems to generate for PowerPC 
32-bit and handles complex type passing/return via general registers 
(the second option). All failures are gone.

The problem here is if some other target/compiler is using the other 
variation. So, for those that have a PowerPC 32-bit handy, can you 
confirm it works reliably? I'm thinking AIX, Darwin or some other eabi 
target.

Otherwise, does this look reasonable?

Regards,
Luis

2014-06-26  Luis Machado  <lgustavo@codesourcery.com>

	* ppc-sysv-tdep.c (ppc_sysv_abi_push_dummy_call): Explicitly
	handle passing of complex arguments.
	(do_ppc_sysv_return_value): Explicitly handle return of
	complex types.

diff --git a/gdb/ppc-sysv-tdep.c b/gdb/ppc-sysv-tdep.c
index 1a880a6..2ea7796 100644
--- a/gdb/ppc-sysv-tdep.c
+++ b/gdb/ppc-sysv-tdep.c
@@ -269,6 +269,57 @@ ppc_sysv_abi_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
 		  greg += 4;
 		}
 	    }
+	  else if (TYPE_CODE (type) == TYPE_CODE_COMPLEX)
+	    {
+	      int lgpr = 11;
+	      int type_size = TYPE_LENGTH (type);
+	      int ngpr = type_size / tdep->wordsize;
+
+	      /* The PowerPC Unified 32-bit ABI states that complex types should
+		 be handled in two different ways.  Either they are passed via
+		 general registers or they are returned as a pointer, in a
+		 general register, to an area that contains the data.
+
+		 Unfortunately there is no straightforward way to decide what
+    		 variation a program is using.  Therefore we assume the GCC
+    		 mechanism of passing the complex data in general registers.
+
+		 Float complex uses 2 consecutive GPR's.
+
+		 Double complex uses 4 consecutive GPR's.
+
+		 Long Double complex uses 4 or 8 consecutive GPR's, depending on
+    		 whether the long double is represented as a double or as a
+    		 128-bit entity.
+
+		 Scalar-based complex types are passed in the same way as their
+		 floating point counterparts.  */
+
+	      /* Check if we should pass this parameter in registers or
+		 stack.  */
+	      if (ngpr + greg > lgpr)
+		{
+		  /* Pass parameter in the stack.  */
+		  argoffset = align_up (argoffset, 8);
+		  if (write_pass)
+		    write_memory (sp + argoffset, val, len);
+		  argoffset += len;
+		}
+	      else
+		{
+		  /* Pass the parameter in registers.  */
+		  if (write_pass)
+		    {
+		      int i;
+
+		      for (i = 0; i < ngpr; i++)
+			regcache_cooked_write (regcache,
+					       tdep->ppc_gp0_regnum + greg + i,
+					       val + i * 4);
+		    }
+		  greg += ngpr;
+		}
+	    }
 	  else if (TYPE_CODE (type) == TYPE_CODE_DECFLOAT && len <= 8
 		   && !tdep->soft_float)
 	    {
@@ -724,6 +775,45 @@ do_ppc_sysv_return_value (struct gdbarch *gdbarch, struct type *func_type,
 	}
       return RETURN_VALUE_REGISTER_CONVENTION;
     }
+
+  /* The PowerPC Unified 32-bit ABI handles return of complex types in two
+     different ways.  Either they are returned via general registers or they are
+     returned as a pointer, in a general register, to an area that contains the
+     data.
+
+     Unfortunately there is no straightforward way to decide what variation a
+     program is using.  Therefore we assume the GCC mechanism of returning the
+     complex data in general registers.
+
+     Float complex uses 2 consecutive GPR's.
+
+     Double complex uses 4 consecutive GPR's.
+
+     Long Double complex uses 4 or 8 consecutive GPR's, depending on whether the
+     long double is represented as a double or as a 128-bit entity.
+
+     Scalar-based complex types are returned in the same way as their floating
+     point counterparts.  */
+  if (TYPE_CODE (type) == TYPE_CODE_COMPLEX)
+    {
+      int i, nregs;
+      int return_reg = tdep->ppc_gp0_regnum + 3;
+
+      nregs = TYPE_LENGTH (type) / tdep->wordsize;
+
+      for (i = 0; i < nregs; i++)
+	{
+	  if (readbuf)
+	    regcache_cooked_read (regcache, return_reg + i,
+				  readbuf + i * tdep->wordsize);
+	  if (writebuf)
+	    regcache_cooked_write (regcache, return_reg + i,
+				   writebuf + i * tdep->wordsize);
+	}
+	    
+      return RETURN_VALUE_REGISTER_CONVENTION;
+    }
+
   if (TYPE_CODE (type) == TYPE_CODE_FLT
       && TYPE_LENGTH (type) == 16
       && !tdep->soft_float