[PATCH] MIPS: Add a GNU attribute for -mips32 -mfp64 objects

[PATCH] MIPS: Add a GNU attribute for -mips32 -mfp64 objects

[Thiemo Seufer]

Hello All,

the appended patch extends the exisiting GNU attribute which tags the
MIPS floating point ABI variant. The new tag is used for MIPS32 R2
CPUs which allow to run the FPU in a mode with 64-bit wide registers.
I failed to come up with a better name than "-mips32r2 -mfp64", which
are the command line options to select this mode.

While I wrote this patch I noticed that the tagging takes only place
when the respective gnu_attribute is found in the source code. This
leaves objects created from assembly untagged. I wonder if it is a good
idea to generally add a FP ABI attribute, derived from the assembler's
command line flags, unless this is overridden by a gnu_attribute
directive in the source. Is there a backward compatibility issue I fail
to see, or some other effect which makes this a bad idea?


Thiemo


2007-11-14  Thiemo Seufer  <ths@mips.com>

	[ld/testsuite/ChangeLog]
	* ld-mips-elf/attr-gnu-4-14.d, ld-mips-elf/attr-gnu-4-41.d:
	Adjust warning message for -mfp64 flag.
	* ld-mips-elf/attr-gnu-4-5.s, ld-mips-elf/attr-gnu-4-04.d,
	ld-mips-elf/attr-gnu-4-51.d, ld-mips-elf/attr-gnu-4-05.d,
	ld-mips-elf/attr-gnu-4-15.d, ld-mips-elf/attr-gnu-4-24.d,
	ld-mips-elf/attr-gnu-4-25.d, ld-mips-elf/attr-gnu-4-34.d,
	ld-mips-elf/attr-gnu-4-35.d, ld-mips-elf/attr-gnu-4-42.d,
	ld-mips-elf/attr-gnu-4-43.d, ld-mips-elf/attr-gnu-4-44.d,
	ld-mips-elf/attr-gnu-4-45.d, ld-mips-elf/attr-gnu-4-40.d,
	ld-mips-elf/attr-gnu-4-14.d: New testcases files.
	* ld-mips-elf/mips-elf.exp: Run new testcases.

	[binutils/ChangeLog]
	* readelf.c (display_mips_gnu_attribute): Recognize -mips32r2 -mfp64
	objects.

	[include/ChangeLog]
	* elf/mips.h (Tag_GNU_MIPS_ABI_FP): Mention -mips32r2 -mfp64 variant
	in comment.

	[bfd/ChangeLog]
	* elfxx-mips.c (mips_elf_merge_obj_attributes): Handle -mips32r2
	-mfp64 attribute.


Index: head/bfd/elfxx-mips.c
===================================================================
--- head.orig/bfd/elfxx-mips.c	2007-11-14 19:15:45.000000000 +0000
+++ head/bfd/elfxx-mips.c	2007-11-14 19:15:49.000000000 +0000
@@ -11055,11 +11055,11 @@
 	out_attr[Tag_GNU_MIPS_ABI_FP].i = in_attr[Tag_GNU_MIPS_ABI_FP].i;
       else if (in_attr[Tag_GNU_MIPS_ABI_FP].i == 0)
 	;
-      else if (in_attr[Tag_GNU_MIPS_ABI_FP].i > 3)
+      else if (in_attr[Tag_GNU_MIPS_ABI_FP].i > 4)
 	_bfd_error_handler
 	  (_("Warning: %B uses unknown floating point ABI %d"), ibfd,
 	   in_attr[Tag_GNU_MIPS_ABI_FP].i);
-      else if (out_attr[Tag_GNU_MIPS_ABI_FP].i > 3)
+      else if (out_attr[Tag_GNU_MIPS_ABI_FP].i > 4)
 	_bfd_error_handler
 	  (_("Warning: %B uses unknown floating point ABI %d"), obfd,
 	   out_attr[Tag_GNU_MIPS_ABI_FP].i);
@@ -11081,6 +11081,12 @@
 		   obfd, ibfd);
 		break;
 
+	      case 4:
+		_bfd_error_handler
+		  (_("Warning: %B uses -msingle-float, %B uses -mips32r2 -mfp64"),
+		   obfd, ibfd);
+		break;
+
 	      default:
 		abort ();
 	      }
@@ -11101,6 +11107,12 @@
 		   obfd, ibfd);
 		break;
 
+	      case 4:
+		_bfd_error_handler
+		  (_("Warning: %B uses -mdouble-float, %B uses -mips32r2 -mfp64"),
+		   obfd, ibfd);
+		break;
+
 	      default:
 		abort ();
 	      }
@@ -11111,6 +11123,7 @@
 	      {
 	      case 1:
 	      case 2:
+	      case 4:
 		_bfd_error_handler
 		  (_("Warning: %B uses hard float, %B uses soft float"),
 		   ibfd, obfd);
@@ -11121,6 +11134,32 @@
 	      }
 	    break;
 
+	  case 4:
+	    switch (in_attr[Tag_GNU_MIPS_ABI_FP].i)
+	      {
+	      case 1:
+		_bfd_error_handler
+		  (_("Warning: %B uses -msingle-float, %B uses -mips32r2 -mfp64"),
+		   ibfd, obfd);
+		break;
+
+	      case 2:
+		_bfd_error_handler
+		  (_("Warning: %B uses -mdouble-float, %B uses -mips32r2 -mfp64"),
+		   ibfd, obfd);
+		break;
+
+	      case 3:
+		_bfd_error_handler
+		  (_("Warning: %B uses hard float, %B uses soft float"),
+		   obfd, ibfd);
+		break;
+
+	      default:
+		abort ();
+	      }
+	    break;
+
 	  default:
 	    abort ();
 	  }
Index: head/include/elf/mips.h
===================================================================
--- head.orig/include/elf/mips.h	2007-11-14 19:01:30.000000000 +0000
+++ head/include/elf/mips.h	2007-11-14 19:15:49.000000000 +0000
@@ -1012,9 +1012,9 @@
   /* 0-3 are generic.  */
   Tag_GNU_MIPS_ABI_FP = 4, /* Value 1 for hard-float -mdouble-float, 2
 			      for hard-float -msingle-float, 3 for
-			      soft-float; 0 for not tagged or not
-			      using any ABIs affected by the
-			      differences.  */
+			      soft-float, 4 for -mips32r2 -mfp64; 0 for
+			      not tagged or not using any ABIs affected
+			      by the differences.  */
 };
 
 #endif /* _ELF_MIPS_H */
Index: head/binutils/readelf.c
===================================================================
--- head.orig/binutils/readelf.c	2007-11-14 19:01:30.000000000 +0000
+++ head/binutils/readelf.c	2007-11-14 19:15:49.000000000 +0000
@@ -8833,6 +8833,9 @@
 	case 3:
 	  printf ("Soft float\n");
 	  break;
+	case 4:
+	  printf ("64-bit float (-mips32r2 -mfp64)\n");
+	  break;
 	default:
 	  printf ("??? (%d)\n", val);
 	  break;
Index: head/ld/testsuite/ld-mips-elf/attr-gnu-4-5.s
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/attr-gnu-4-5.s	2007-11-14 19:15:49.000000000 +0000
@@ -0,0 +1 @@
+.gnu_attribute 4,5
Index: head/ld/testsuite/ld-mips-elf/mips-elf.exp
===================================================================
--- head.orig/ld/testsuite/ld-mips-elf/mips-elf.exp	2007-11-14 19:01:30.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/mips-elf.exp	2007-11-14 19:15:49.000000000 +0000
@@ -285,17 +285,30 @@
 run_dump_test "attr-gnu-4-01"
 run_dump_test "attr-gnu-4-02"
 run_dump_test "attr-gnu-4-03"
+run_dump_test "attr-gnu-4-04"
+run_dump_test "attr-gnu-4-05"
 run_dump_test "attr-gnu-4-10"
 run_dump_test "attr-gnu-4-11"
 run_dump_test "attr-gnu-4-12"
 run_dump_test "attr-gnu-4-13"
 run_dump_test "attr-gnu-4-14"
+run_dump_test "attr-gnu-4-15"
 run_dump_test "attr-gnu-4-20"
 run_dump_test "attr-gnu-4-21"
 run_dump_test "attr-gnu-4-22"
 run_dump_test "attr-gnu-4-23"
+run_dump_test "attr-gnu-4-24"
+run_dump_test "attr-gnu-4-25"
 run_dump_test "attr-gnu-4-30"
 run_dump_test "attr-gnu-4-31"
 run_dump_test "attr-gnu-4-32"
 run_dump_test "attr-gnu-4-33"
+run_dump_test "attr-gnu-4-34"
+run_dump_test "attr-gnu-4-35"
+run_dump_test "attr-gnu-4-40"
 run_dump_test "attr-gnu-4-41"
+run_dump_test "attr-gnu-4-42"
+run_dump_test "attr-gnu-4-43"
+run_dump_test "attr-gnu-4-44"
+run_dump_test "attr-gnu-4-45"
+run_dump_test "attr-gnu-4-51"
Index: head/ld/testsuite/ld-mips-elf/attr-gnu-4-04.d
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/attr-gnu-4-04.d	2007-11-14 19:15:49.000000000 +0000
@@ -0,0 +1,10 @@
+#source: attr-gnu-4-0.s
+#source: attr-gnu-4-4.s
+#as: -EB -32
+#ld: -r -melf32btsmip
+#readelf: -A
+#target: mips*-*-*
+
+Attribute Section: gnu
+File Attributes
+  Tag_GNU_MIPS_ABI_FP: 64-bit float \(-mips32r2 -mfp64\)
Index: head/ld/testsuite/ld-mips-elf/attr-gnu-4-51.d
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/attr-gnu-4-51.d	2007-11-14 19:15:49.000000000 +0000
@@ -0,0 +1,6 @@
+#source: attr-gnu-4-5.s
+#source: attr-gnu-4-1.s
+#as: -EB -32
+#ld: -r -melf32btsmip
+#warning: Warning: .* uses unknown floating point ABI 5
+#target: mips*-*-*
Index: head/ld/testsuite/ld-mips-elf/attr-gnu-4-05.d
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/attr-gnu-4-05.d	2007-11-14 19:15:49.000000000 +0000
@@ -0,0 +1,10 @@
+#source: attr-gnu-4-0.s
+#source: attr-gnu-4-5.s
+#as: -EB -32
+#ld: -r -melf32btsmip
+#readelf: -A
+#target: mips*-*-*
+
+Attribute Section: gnu
+File Attributes
+  Tag_GNU_MIPS_ABI_FP: \?\?\? \(5\)
Index: head/ld/testsuite/ld-mips-elf/attr-gnu-4-15.d
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/attr-gnu-4-15.d	2007-11-14 19:15:49.000000000 +0000
@@ -0,0 +1,11 @@
+#source: attr-gnu-4-1.s
+#source: attr-gnu-4-5.s
+#as: -EB -32
+#ld: -r -melf32btsmip
+#readelf: -A
+#warning: Warning: .* uses unknown floating point ABI 5
+#target: mips*-*-*
+
+Attribute Section: gnu
+File Attributes
+  Tag_GNU_MIPS_ABI_FP: Hard float \(-mdouble-float\)
Index: head/ld/testsuite/ld-mips-elf/attr-gnu-4-24.d
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/attr-gnu-4-24.d	2007-11-14 19:15:49.000000000 +0000
@@ -0,0 +1,6 @@
+#source: attr-gnu-4-2.s
+#source: attr-gnu-4-4.s
+#as: -EB -32
+#ld: -r -melf32btsmip
+#warning: Warning: .* uses -mips32r2 -mfp64
+#target: mips*-*-*
Index: head/ld/testsuite/ld-mips-elf/attr-gnu-4-25.d
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/attr-gnu-4-25.d	2007-11-14 19:15:49.000000000 +0000
@@ -0,0 +1,11 @@
+#source: attr-gnu-4-2.s
+#source: attr-gnu-4-5.s
+#as: -EB -32
+#ld: -r -melf32btsmip
+#readelf: -A
+#warning: Warning: .* uses unknown floating point ABI 5
+#target: mips*-*-*
+
+Attribute Section: gnu
+File Attributes
+  Tag_GNU_MIPS_ABI_FP: Hard float \(-msingle-float\)
Index: head/ld/testsuite/ld-mips-elf/attr-gnu-4-34.d
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/attr-gnu-4-34.d	2007-11-14 19:15:49.000000000 +0000
@@ -0,0 +1,6 @@
+#source: attr-gnu-4-3.s
+#source: attr-gnu-4-4.s
+#as: -EB -32
+#ld: -r -melf32btsmip
+#warning: Warning: .* uses hard float, .* uses soft float
+#target: mips*-*-*
Index: head/ld/testsuite/ld-mips-elf/attr-gnu-4-35.d
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/attr-gnu-4-35.d	2007-11-14 19:15:49.000000000 +0000
@@ -0,0 +1,11 @@
+#source: attr-gnu-4-3.s
+#source: attr-gnu-4-5.s
+#as: -EB -32
+#ld: -r -melf32btsmip
+#readelf: -A
+#warning: Warning: .* uses unknown floating point ABI 5
+#target: mips*-*-*
+
+Attribute Section: gnu
+File Attributes
+  Tag_GNU_MIPS_ABI_FP: Soft float
Index: head/ld/testsuite/ld-mips-elf/attr-gnu-4-42.d
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/attr-gnu-4-42.d	2007-11-14 19:15:49.000000000 +0000
@@ -0,0 +1,6 @@
+#source: attr-gnu-4-4.s
+#source: attr-gnu-4-2.s
+#as: -EB -32
+#ld: -r -melf32btsmip
+#warning: Warning: .* uses -mips32r2 -mfp64
+#target: mips*-*-*
Index: head/ld/testsuite/ld-mips-elf/attr-gnu-4-43.d
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/attr-gnu-4-43.d	2007-11-14 19:15:49.000000000 +0000
@@ -0,0 +1,6 @@
+#source: attr-gnu-4-4.s
+#source: attr-gnu-4-3.s
+#as: -EB -32
+#ld: -r -melf32btsmip
+#warning: Warning: .* uses hard float, .* uses soft float
+#target: mips*-*-*
Index: head/ld/testsuite/ld-mips-elf/attr-gnu-4-44.d
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/attr-gnu-4-44.d	2007-11-14 19:15:49.000000000 +0000
@@ -0,0 +1,10 @@
+#source: attr-gnu-4-4.s
+#source: attr-gnu-4-4.s
+#as: -EB -32
+#ld: -r -melf32btsmip
+#readelf: -A
+#target: mips*-*-*
+
+Attribute Section: gnu
+File Attributes
+  Tag_GNU_MIPS_ABI_FP: 64-bit float \(-mips32r2 -mfp64\)
Index: head/ld/testsuite/ld-mips-elf/attr-gnu-4-45.d
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/attr-gnu-4-45.d	2007-11-14 19:15:49.000000000 +0000
@@ -0,0 +1,10 @@
+#source: attr-gnu-4-4.s
+#source: attr-gnu-4-5.s
+#as: -EB -32
+#ld: -r -melf32btsmip
+#warning: Warning: .* uses unknown floating point ABI 5
+#target: mips*-*-*
+
+Attribute Section: gnu
+File Attributes
+  Tag_GNU_MIPS_ABI_FP: 64-bit float \(-mips32r2 -mfp64\)
Index: head/ld/testsuite/ld-mips-elf/attr-gnu-4-40.d
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/attr-gnu-4-40.d	2007-11-14 19:15:49.000000000 +0000
@@ -0,0 +1,10 @@
+#source: attr-gnu-4-4.s
+#source: attr-gnu-4-0.s
+#as: -EB -32
+#ld: -r -melf32btsmip
+#readelf: -A
+#target: mips*-*-*
+
+Attribute Section: gnu
+File Attributes
+  Tag_GNU_MIPS_ABI_FP: 64-bit float \(-mips32r2 -mfp64\)
Index: head/ld/testsuite/ld-mips-elf/attr-gnu-4-14.d
===================================================================
--- head.orig/ld/testsuite/ld-mips-elf/attr-gnu-4-14.d	2007-11-14 19:01:30.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/attr-gnu-4-14.d	2007-11-14 19:15:49.000000000 +0000
@@ -2,5 +2,5 @@
 #source: attr-gnu-4-4.s
 #as: -EB -32
 #ld: -r -melf32btsmip
-#warning: Warning: .* uses unknown floating point ABI 4
+#warning: Warning: .* uses -msingle-float, .* uses -mips32r2 -mfp64
 #target: mips*-*-*
Index: head/ld/testsuite/ld-mips-elf/attr-gnu-4-41.d
===================================================================
--- head.orig/ld/testsuite/ld-mips-elf/attr-gnu-4-41.d	2007-11-14 19:01:30.000000000 +0000
+++ head/ld/testsuite/ld-mips-elf/attr-gnu-4-41.d	2007-11-14 19:15:49.000000000 +0000
@@ -2,5 +2,5 @@
 #source: attr-gnu-4-1.s
 #as: -EB -32
 #ld: -r -melf32btsmip
-#warning: Warning: .* uses unknown floating point ABI 4
+#warning: Warning: .* uses -msingle-float, .* uses -mips32r2 -mfp64
 #target: mips*-*-*

Re: [PATCH] MIPS: Add a GNU attribute for -mips32 -mfp64 objects

[Joseph S. Myers]

On Wed, 14 Nov 2007, Thiemo Seufer wrote:

> While I wrote this patch I noticed that the tagging takes only place
> when the respective gnu_attribute is found in the source code. This
> leaves objects created from assembly untagged. I wonder if it is a good
> idea to generally add a FP ABI attribute, derived from the assembler's
> command line flags, unless this is overridden by a gnu_attribute
> directive in the source. Is there a backward compatibility issue I fail
> to see, or some other effect which makes this a bad idea?

I didn't think the compiler passed the -msoft-float/-mhard-float ABI 
information to the assembler, so this could cause problems with incorrect 
tagging when older compilers are used with newer assemblers.  The ABI is a 
separate matter from what instructions are enabled, and a valid ABI is 
being compatible with both hard and soft float; a file with purely integer 
instructions could be a soft-float file if the functions are taking 
floating-point parameters, or a file compatible with both if they are 
taking integer parameters.  How would you deduce the C language function 
call compatibility of an object (which is what the attributes describe) 
from the assembler source and command line options?

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: [PATCH] MIPS: Add a GNU attribute for -mips32 -mfp64 objects

[Joseph S. Myers]

On Wed, 14 Nov 2007, Thiemo Seufer wrote:

> 	[ld/testsuite/ChangeLog]
> 	[binutils/ChangeLog]
> 	[include/ChangeLog]
> 	[bfd/ChangeLog]

The attributes are now documented in gas/doc/as.texinfo so that needs 
updating as well.

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: [PATCH] MIPS: Add a GNU attribute for -mips32 -mfp64 objects

[Thiemo Seufer]

Joseph S. Myers wrote:
> On Wed, 14 Nov 2007, Thiemo Seufer wrote:
> 
> > While I wrote this patch I noticed that the tagging takes only place
> > when the respective gnu_attribute is found in the source code. This
> > leaves objects created from assembly untagged. I wonder if it is a good
> > idea to generally add a FP ABI attribute, derived from the assembler's
> > command line flags, unless this is overridden by a gnu_attribute
> > directive in the source. Is there a backward compatibility issue I fail
> > to see, or some other effect which makes this a bad idea?
> 
> I didn't think the compiler passed the -msoft-float/-mhard-float ABI 
> information to the assembler, so this could cause problems with incorrect 
> tagging when older compilers are used with newer assemblers.

The compiler currently doesn't pass down the -m*-float options. So
the assembler won't see the option, and therefore won't tag the object.
The -mfp64 is passed, but it is AFAICS unlikely to generate invalid
tagging: Presumably the reason to use the compiler's -mfp64 option is
to generate 64-bit FP code, which isn't compatible to the other variants
as soon as e.g. a mfhc1 instruction is used.

The idea is to pass the relevent options to the assembler (at least for
.s/.S source files, for compiler generated files it would be redundant).

> The ABI is a 
> separate matter from what instructions are enabled, and a valid ABI is 
> being compatible with both hard and soft float; a file with purely integer 
> instructions could be a soft-float file if the functions are taking 
> floating-point parameters, or a file compatible with both if they are 
> taking integer parameters.  How would you deduce the C language function 
> call compatibility of an object (which is what the attributes describe) 
> from the assembler source and command line options?

I think of all those, soft-float and "no-float" are the only compatible
ones. They would stay link compatible, as "no FP option" means tag 0.

A hard-float object which happens not to use floating point at all wouldn't
be link compatible any more, this is the same effect which was evidently
regarded as acceptable in newer GCC compilers.


Thiemo

Re: [PATCH] MIPS: Add a GNU attribute for -mips32 -mfp64 objects

[Joseph S. Myers]

On Thu, 15 Nov 2007, Thiemo Seufer wrote:

> The -mfp64 is passed, but it is AFAICS unlikely to generate invalid
> tagging: Presumably the reason to use the compiler's -mfp64 option is
> to generate 64-bit FP code, which isn't compatible to the other variants
> as soon as e.g. a mfhc1 instruction is used.

This tagging in the assembler would need of course to be conditioned on 
generating O32 code, since as I understand it -mfp64 only selects a novel 
ABI variant for O32, N32 and N64 are covered by the normal hard-float ABI 
setting.

> The idea is to pass the relevent options to the assembler (at least for
> .s/.S source files, for compiler generated files it would be redundant).

Indeed - for compiler generated files, if you need to modify the compiler 
to pass down the option, you may as well modify it to set the attribute 
itself.

> A hard-float object which happens not to use floating point at all wouldn't
> be link compatible any more, this is the same effect which was evidently
> regarded as acceptable in newer GCC compilers.

Acceptable but not ideal; we'd hope in future to make GCC detect whether 
the particular source file is or is not affected, and then set the 
attribute saying it's unaffected if it's unaffected.  I suppose unaffected 
assembler files can always explicitly set the attribute to say so.

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: [PATCH] MIPS: Add a GNU attribute for -mips32 -mfp64 objects

[Richard Sandiford]

Thiemo Seufer <ths@networkno.de> writes:
> Joseph S. Myers wrote:
>> On Wed, 14 Nov 2007, Thiemo Seufer wrote:
>> 
>> > While I wrote this patch I noticed that the tagging takes only place
>> > when the respective gnu_attribute is found in the source code. This
>> > leaves objects created from assembly untagged. I wonder if it is a good
>> > idea to generally add a FP ABI attribute, derived from the assembler's
>> > command line flags, unless this is overridden by a gnu_attribute
>> > directive in the source. Is there a backward compatibility issue I fail
>> > to see, or some other effect which makes this a bad idea?
>> 
>> I didn't think the compiler passed the -msoft-float/-mhard-float ABI 
>> information to the assembler, so this could cause problems with incorrect 
>> tagging when older compilers are used with newer assemblers.
>
> The compiler currently doesn't pass down the -m*-float options. So
> the assembler won't see the option, and therefore won't tag the object.
> The -mfp64 is passed, but it is AFAICS unlikely to generate invalid
> tagging: Presumably the reason to use the compiler's -mfp64 option is
> to generate 64-bit FP code, which isn't compatible to the other variants
> as soon as e.g. a mfhc1 instruction is used.
>
> The idea is to pass the relevent options to the assembler (at least for
> .s/.S source files, for compiler generated files it would be redundant).

I agree with Joseph here.  Although it's redundant to specify -mfp64
with -msoft-float, it isn't actively wrong.  The options have traditionally
been orthogonal.  I don't think the assembler should assume that -mfp64
implies -mhard-float.

I agree that it's a good idea to make -mfp64 -mgp32 a separate value for
the existing attribute (rather than introducing a new attribute, say).
But at the moment, only the compiler or assembly programmer knows the
right value for the attribute.

FWIW, I think it would be perfectly OK to add an extra case to gcc's
attribute code now, even though we're in stage 3.  I'll volunteer to
do that if you don't have a patch already.

Richard

Re: [PATCH] MIPS: Add a GNU attribute for -mips32 -mfp64 objects

[Paul Koning]

>>>>> "Richard" == Richard Sandiford <rsandifo@nildram.co.uk> writes:

 Richard> I agree with Joseph here.  Although it's redundant to
 Richard> specify -mfp64 with -msoft-float, it isn't actively wrong.
 Richard> The options have traditionally been orthogonal.  I don't
 Richard> think the assembler should assume that -mfp64 implies
 Richard> -mhard-float.

It seems strange, since -msoft-float means no float registers, while
-mfp64 says there are float registers and they are 64 bits wide.

       paul

Re: [PATCH] MIPS: Add a GNU attribute for -mips32 -mfp64 objects

[Richard Sandiford]

Paul Koning <pkoning@equallogic.com> writes:
>>>>>> "Richard" == Richard Sandiford <rsandifo@nildram.co.uk> writes:
>
>  Richard> I agree with Joseph here.  Although it's redundant to
>  Richard> specify -mfp64 with -msoft-float, it isn't actively wrong.
>  Richard> The options have traditionally been orthogonal.  I don't
>  Richard> think the assembler should assume that -mfp64 implies
>  Richard> -mhard-float.
>
> It seems strange, since -msoft-float means no float registers, while
> -mfp64 says there are float registers and they are 64 bits wide.

Well, -mhard-float and -msoft-float are ABI options.  -mfp64 is
an architectural configuration option, and only affects calling
conventions when combined with -mhard-float.  It is perfectly
possible to write code that conforms to the soft-float ABI while
still using FPU instructions within a function.  (Strictly speaking,
the use of FPU instructions is also part of the ABI.  But it isn't
what this attribute specifies; this attribute is about the calling
conventions.)

The practical example of the difference is MIPS16.  -mhard-float
-mips16 doesn't say "use the FPU from MIPS16 code"; you can't.
It says instead that the hard-float ABI is in effect, and that
we need to use special stubs to interface with non-MIPS16 code.

Richard

Re: [PATCH] MIPS: Add a GNU attribute for -mips32 -mfp64 objects

[Thiemo Seufer]

Richard Sandiford wrote:
> Paul Koning <pkoning@equallogic.com> writes:
> >>>>>> "Richard" == Richard Sandiford <rsandifo@nildram.co.uk> writes:
> >
> >  Richard> I agree with Joseph here.  Although it's redundant to
> >  Richard> specify -mfp64 with -msoft-float, it isn't actively wrong.
> >  Richard> The options have traditionally been orthogonal.  I don't
> >  Richard> think the assembler should assume that -mfp64 implies
> >  Richard> -mhard-float.
> >
> > It seems strange, since -msoft-float means no float registers, while
> > -mfp64 says there are float registers and they are 64 bits wide.
> 
> Well, -mhard-float and -msoft-float are ABI options.  -mfp64 is
> an architectural configuration option, and only affects calling
> conventions when combined with -mhard-float.

But "-mhard-float -mfp64" constitutes a new ABI variant. This is
the case I want to cover. The "-msoft-float -mfp64" should stay
tagged as soft float object.

> It is perfectly
> possible to write code that conforms to the soft-float ABI while
> still using FPU instructions within a function.

I wonder how relevant this possibility is in practice. To me it
sounds too subtle to be of much use.

> (Strictly speaking,
> the use of FPU instructions is also part of the ABI.  But it isn't
> what this attribute specifies; this attribute is about the calling
> conventions.)
> The practical example of the difference is MIPS16.  -mhard-float
> -mips16 doesn't say "use the FPU from MIPS16 code"; you can't.
> It says instead that the hard-float ABI is in effect, and that
> we need to use special stubs to interface with non-MIPS16 code.

And, for completeness, we have "-mips32r2 -mips16 -mhard-float -mfp64",
which tells the compiler to generate different stubs than the ones
needed for the standard hard float.


Thiemo

Re: [PATCH] MIPS: Add a GNU attribute for -mips32 -mfp64 objects

[Richard Sandiford]

Thiemo Seufer <ths@networkno.de> writes:
> Richard Sandiford wrote:
>> Paul Koning <pkoning@equallogic.com> writes:
>> >>>>>> "Richard" == Richard Sandiford <rsandifo@nildram.co.uk> writes:
>> >
>> >  Richard> I agree with Joseph here.  Although it's redundant to
>> >  Richard> specify -mfp64 with -msoft-float, it isn't actively wrong.
>> >  Richard> The options have traditionally been orthogonal.  I don't
>> >  Richard> think the assembler should assume that -mfp64 implies
>> >  Richard> -mhard-float.
>> >
>> > It seems strange, since -msoft-float means no float registers, while
>> > -mfp64 says there are float registers and they are 64 bits wide.
>> 
>> Well, -mhard-float and -msoft-float are ABI options.  -mfp64 is
>> an architectural configuration option, and only affects calling
>> conventions when combined with -mhard-float.
>
> But "-mhard-float -mfp64" constitutes a new ABI variant. This is
> the case I want to cover. The "-msoft-float -mfp64" should stay
> tagged as soft float object.

Right.  That's why in the other paragraph I agreed that adding a new
value to the current enumeration was the right way to go.  I just don't
think GAS has enough information to generate the enumeration value itself.

> And, for completeness, we have "-mips32r2 -mips16 -mhard-float -mfp64",
> which tells the compiler to generate different stubs than the ones
> needed for the standard hard float.

Right.  In theory, -mips16 supports all hard-float and soft-float ABI
combinations for o32 and o64 (including -msingle-float).

Richard