Regression of GCC >= 4.8.5 for 32-bit powerpc

[Rin Okuyama <rokuyama%rk.phys.keio.ac.jp@localhost>]

GCC >= 4.8.5 passes ".machine ppc" pseudo-op to assembler for 32-bit
powerpc:

src/external/gpl3/gcc/dist/gcc/config/rs6000/rs6000.c

  5187  #ifdef USING_ELFOS_H
  5188    if (rs6000_default_cpu == 0 || rs6000_default_cpu[0] == '\0'
  5189        || !global_options_set.x_rs6000_cpu_index)
  5190      {
  5191        fputs ("\t.machine ", asm_out_file);
  5192        if ((rs6000_isa_flags & OPTION_MASK_DIRECT_MOVE) != 0)
  5193          fputs ("power8\n", asm_out_file);
  5194        else if ((rs6000_isa_flags & OPTION_MASK_POPCNTD) != 0)
  5195          fputs ("power7\n", asm_out_file);
  5196        else if ((rs6000_isa_flags & OPTION_MASK_CMPB) != 0)
  5197          fputs ("power6\n", asm_out_file);
  5198        else if ((rs6000_isa_flags & OPTION_MASK_POPCNTB) != 0)
  5199          fputs ("power5\n", asm_out_file);
  5200        else if ((rs6000_isa_flags & OPTION_MASK_MFCRF) != 0)
  5201          fputs ("power4\n", asm_out_file);
  5202        else if ((rs6000_isa_flags & OPTION_MASK_POWERPC64) != 0)
  5203          fputs ("ppc64\n", asm_out_file);
  5204        else
  5205          fputs ("ppc\n", asm_out_file);
  5206      }
  5207  #endif

This pseudo-op discards CPU type specified by compiler option
"-mcpu=XXX" or "-Wa,-mXXX". As a result, some mnemonics are misassembled
into instructions for generic ppc. This results in broken kernel for IBM
405, where indices of some special purpose registers are different from
those in generic ppc, cf. port-powerpc/51366:

  http://gnats.netbsd.org/51366

This is a clearly regression of GCC. The logic raised above seem to be
intended for 64-bit powerpc; without it, gas cannot assemble codes
generated by GCC for 64-bit powerpc. I therefore propose to restrict
usage of ".machine" pseudo-op to the 64-bit machines like this:

====
--- src/external/gpl3/gcc/dist/gcc/config/rs6000/rs6000.c.orig	2016-07-26 20:35:20.391415369 +0900
+++ src/external/gpl3/gcc/dist/gcc/config/rs6000/rs6000.c	2016-07-26 21:07:17.973106045 +0900
@@ -5185,8 +5185,13 @@
     }
 
 #ifdef USING_ELFOS_H
-  if (rs6000_default_cpu == 0 || rs6000_default_cpu[0] == '\0'
-      || !global_options_set.x_rs6000_cpu_index)
+/*
+ * XXX .machine overrides CPU type specified by -mcpu or -Wa,-m options, which
+ * can result in corrupted output with inline assembler for ppc32.
+ */
+  if ((rs6000_default_cpu == 0 || rs6000_default_cpu[0] == '\0'
+	|| !global_options_set.x_rs6000_cpu_index)
+      && (rs6000_isa_flags & OPTION_MASK_POWERPC64) != 0)
     {
       fputs ("\t.machine ", asm_out_file);
       if ((rs6000_isa_flags & OPTION_MASK_DIRECT_MOVE) != 0)
@@ -5199,10 +5204,8 @@
 	fputs ("power5\n", asm_out_file);
       else if ((rs6000_isa_flags & OPTION_MASK_MFCRF) != 0)
 	fputs ("power4\n", asm_out_file);
-      else if ((rs6000_isa_flags & OPTION_MASK_POWERPC64) != 0)
-	fputs ("ppc64\n", asm_out_file);
       else
-	fputs ("ppc\n", asm_out_file);
+	fputs ("ppc64\n", asm_out_file);
     }
 #endif
====
 
Could I commit this patch? Any comments or suggestions?

Thanks,
Rin