MIPS: Provide FPU info and decode FCSR in `info float'

This patch is the V2.  V1 can be found in
https://sourceware.org/ml/gdb-patches/2012-05/msg00938.html
V2 is to address Joel's comment
<https://sourceware.org/ml/gdb-patches/2012-06/msg00289.html> about
keeping dumping floating point registers.  Additionally, command
'info float' prints bits on nan2008 and abs2008.

------------------------------------------------------------------

 The change below provides a MIPS-specific handler for the:

(gdb) info float

command.  It provides information about the FPU type available (if any),
the FPU register width, and decodes the CP1 Floating Point Control and
Status Register (FCSR):

(gdb) print /x $fsr
$1 = 0xff83ffff
(gdb) info float
fpu type: double-precision
reg size: 32 bits
cond    : 0 1 2 3 4 5 6 7
cause   : inexact uflow oflow div0 inval unimp
mask    : inexact uflow oflow div0 inval
flags   : inexact uflow oflow div0 inval
rounding: -inf
flush   : zero

 One point to note about CP1.FCSR are the non-standard Flush-to-Nearest
and Flush-Override bits.  They are not a part of the MIPS architecture and
take two positions reserved for an implementation-dependent use in the
architecture.  They are present in all the FPU implementations made by
MIPS Technologies since the spin-off from SGI.

 I haven't been able to track down a single other MIPS FPU implementation
that would make any use of these bits and they are required to be
hardwired to zero by the architecture specification if unimplemented.
Therefore I think it makes sense to report them in the current way.

 GDB has no guaranteed access to the CP0 Processor Identification (PRId)
register to validate this feature properly and the ID information stored
in the CP1 Floating Point Implementation Register (FIR) is from my
experience not reliable enough (there's no Company ID available there for
once unlike in CP0.PRId and Processor ID is not guaranteed to be unique).

 As a side note we should probably dump CP1.FIR information as well, as
there's useful stuff indicating some FPU features there.  That's material
for another change however.

gdb/

2014-12-18  Nigel Stephens  <nigel@mips.com>
            Maciej W. Rozycki  <macro@codesourcery.com>

	* mips-tdep.c (print_fpu_flags): New function.
	(mips_print_float_info): Likewise.
	(mips_gdbarch_init): Install mips_print_float_info as gdbarch
	print_float_info routine.

gdb/testsuite/

2014-12-18  Nigel Stephens  <nigel@mips.com>
            Maciej W. Rozycki  <macro@codesourcery.com>

	* gdb.base/float.exp: Handle the new output from "info float" on
	MIPS targets.

1 files changed, 93 insertions, 0 deletions

diff --git a/gdb/mips-tdep.c b/gdb/mips-tdep.c
index eb99910..60f43ac 100644
--- a/gdb/mips-tdep.c
+++ b/gdb/mips-tdep.c
@@ -73,6 +73,9 @@ static int micromips_insn_at_pc_has_delay_slot (struct gdbarch *gdbarch,
 static int mips16_insn_at_pc_has_delay_slot (struct gdbarch *gdbarch,
 					     CORE_ADDR addr, int mustbe32);
 
+static void mips_print_float_info (struct gdbarch *, struct ui_file *,
+				   struct frame_info *, const char *);
+
 /* A useful bit in the CP0 status register (MIPS_PS_REGNUM).  */
 /* This bit is set if we are emulating 32-bit FPRs on a 64-bit chip.  */
 #define ST0_FR (1 << 26)
@@ -6387,6 +6390,94 @@ mips_print_register (struct ui_file *file, struct frame_info *frame,
 			      &opts, 0, file);
 }
 
+/* Print IEEE exception condition bits in FLAGS.  */
+
+static void
+print_fpu_flags (struct ui_file *file, int flags)
+{
+  if (flags & (1 << 0))
+    fputs_filtered (" inexact", file);
+  if (flags & (1 << 1))
+    fputs_filtered (" uflow", file);
+  if (flags & (1 << 2))
+    fputs_filtered (" oflow", file);
+  if (flags & (1 << 3))
+    fputs_filtered (" div0", file);
+  if (flags & (1 << 4))
+    fputs_filtered (" inval", file);
+  if (flags & (1 << 5))
+    fputs_filtered (" unimp", file);
+  fputc_filtered ('\n', file);
+}
+
+/* Print interesting information about the floating point processor
+   (if present) or emulator.  */
+
+static void
+mips_print_float_info (struct gdbarch *gdbarch, struct ui_file *file,
+		      struct frame_info *frame, const char *args)
+{
+  int fcsr = mips_regnum (gdbarch)->fp_control_status;
+  enum mips_fpu_type type = MIPS_FPU_TYPE (gdbarch);
+  ULONGEST fcs = 0;
+  int i;
+
+  if (fcsr == -1 || !read_frame_register_unsigned (frame, fcsr, &fcs))
+    type = MIPS_FPU_NONE;
+
+  fprintf_filtered (file, "fpu type: %s\n",
+		    type == MIPS_FPU_DOUBLE ? "double-precision"
+		    : type == MIPS_FPU_SINGLE ? "single-precision"
+		    : "none / unused");
+
+  if (type == MIPS_FPU_NONE)
+    return;
+
+  fprintf_filtered (file, "reg size: %d bits\n",
+		    register_size (gdbarch, mips_regnum (gdbarch)->fp0) * 8);
+
+  fputs_filtered ("cond    :", file);
+  if (fcs & (1 << 23))
+    fputs_filtered (" 0", file);
+  for (i = 1; i <= 7; i++)
+    if (fcs & (1 << (24 + i)))
+      fprintf_filtered (file, " %d", i);
+  fputc_filtered ('\n', file);
+
+  fputs_filtered ("cause   :", file);
+  print_fpu_flags (file, (fcs >> 12) & 0x3f);
+  fputs ("mask    :", stdout);
+  print_fpu_flags (file, (fcs >> 7) & 0x1f);
+  fputs ("flags   :", stdout);
+  print_fpu_flags (file, (fcs >> 2) & 0x1f);
+
+  fputs_filtered ("rounding: ", file);
+  switch (fcs & 3)
+    {
+    case 0: fputs_filtered ("nearest\n", file); break;
+    case 1: fputs_filtered ("zero\n", file); break;
+    case 2: fputs_filtered ("+inf\n", file); break;
+    case 3: fputs_filtered ("-inf\n", file); break;
+    }
+
+  fputs_filtered ("flush   :", file);
+  if (fcs & (1 << 21))
+    fputs_filtered (" nearest", file);
+  if (fcs & (1 << 22))
+    fputs_filtered (" override", file);
+  if (fcs & (1 << 24))
+    fputs_filtered (" zero", file);
+  if ((fcs & (0xb << 21)) == 0)
+    fputs_filtered (" no", file);
+  fputc_filtered ('\n', file);
+
+  fprintf_filtered (file, "nan2008 : %s\n", fcs & (1 << 18) ? "yes" : "no");
+  fprintf_filtered (file, "abs2008 : %s\n", fcs & (1 << 19) ? "yes" : "no");
+  fputc_filtered ('\n', file);
+
+  default_print_float_info (gdbarch, file, frame, args);
+}
+
 /* Replacement for generic do_registers_info.
    Print regs in pretty columns.  */
 
@@ -8737,6 +8828,8 @@ mips_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   set_gdbarch_push_dummy_code (gdbarch, mips_push_dummy_code);
   set_gdbarch_frame_align (gdbarch, mips_frame_align);
 
+  set_gdbarch_print_float_info (gdbarch, mips_print_float_info);
+
   set_gdbarch_convert_register_p (gdbarch, mips_convert_register_p);
   set_gdbarch_register_to_value (gdbarch, mips_register_to_value);
   set_gdbarch_value_to_register (gdbarch, mips_value_to_register);