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[PATCH v2] [MIPS] GAS: Fix Loongson3 LLSC errata


From: Paul Hua <paul.hua.gm@gmail.com>

In some older Loongson 3A1000 processors there is a LL/SC errata that
can cause the CPU to deadlock occasionally.  The details are very
complicated. We find a way to work around this errata by adding a sync
before ll/lld instruction.

This patch also add a configure options
--enable-mips-fix-loongson3-llsc=[yes|no] to enable fix-loongson3-llsc
by config.

v1 -> v2:
  Regenerate configure file with the same version fo autotools,
  to make the patch shorter.

gas/
        * NEWS: Mention -m[no-]fix-loongson3-llsc.
        * configure.ac: Add --enable-mips-fix-loongson3-llsc.
          Define DEFAULT_MIPS_FIX_LOONGSON3_LLSC.
        * config.in: Regenerated.
        * configure: Likewise.
        * config/tc-mips.c (sync_insn, mips_fix_loongson3_llsc):
          New variables.
        (options): New OPTION_FIX_LOONGSON3_LLSC,
          OPTION_NO_FIX_LOONGSON3_LLSC.
        (md_longopts): Add -m[no-]fix-loongson3-llsc.
        (md_begin): Initialize sync insn.
        (fix_loongson3_llsc): New.
        (append_insn): Call fix_loongson3_llsc.
        (md_parse_option): Handle OPTION_FIX_LOONGSON3_LLSC,
          OPTION_NO_FIX_LOONGSON3_LLSC.
        (md_show_usage): Display -m[no-]fix-loongson3-llsc.
        * doc/c-mips.texi: Document -m[no-]fix-loongson3-llsc,
          --enable-mips-fix-loongson3-llsc=[yes|no].
---
 gas/NEWS             |  4 ++++
 gas/config.in        |  3 +++
 gas/config/tc-mips.c | 52 ++++++++++++++++++++++++++++++++++++++++++++
 gas/configure        | 23 ++++++++++++++++++++
 gas/configure.ac     | 18 +++++++++++++++
 gas/doc/c-mips.texi  |  7 ++++++
 6 files changed, 107 insertions(+)

diff --git a/gas/NEWS b/gas/NEWS
index 26f78b08..83634192 100644
--- a/gas/NEWS
+++ b/gas/NEWS
@@ -1,4 +1,8 @@
 -*- text -*-
+* For MIPS, Add -m[no-]fix-loongson3-llsc option to fix (or not) Loongson3 LLSC
+  Errata.  Add a --enable-mips-fix-loongson3-llsc=[yes|no] configure time option
+  to set the default behavior. Set the default if the configure option is not used
+  to "no".
 
 * Add -mvexwig=[0|1] option to x86 assembler to control encoding of
   VEX.W-ignored (WIG) VEX instructions.
diff --git a/gas/config.in b/gas/config.in
index 9c15a070..8a8a4c05 100644
--- a/gas/config.in
+++ b/gas/config.in
@@ -50,6 +50,9 @@
 /* Define to 1 if you want to generate x86 relax relocations by default. */
 #undef DEFAULT_GENERATE_X86_RELAX_RELOCATIONS
 
+/* Define to 1 if you want to fix Loongson3 LLSC Errata by default. */
+#undef DEFAULT_MIPS_FIX_LOONGSON3_LLSC
+
 /* Define to 1 if you want to generate GNU x86 used ISA and feature properties
    by default. */
 #undef DEFAULT_X86_USED_NOTE
diff --git a/gas/config/tc-mips.c b/gas/config/tc-mips.c
index 29420365..e577846c 100644
--- a/gas/config/tc-mips.c
+++ b/gas/config/tc-mips.c
@@ -808,6 +808,9 @@ static struct mips_cl_insn mips16_nop_insn;
 static struct mips_cl_insn micromips_nop16_insn;
 static struct mips_cl_insn micromips_nop32_insn;
 
+/* Sync instructions used by insert sync.  */
+static struct mips_cl_insn sync_insn;
+
 /* The appropriate nop for the current mode.  */
 #define NOP_INSN (mips_opts.mips16					\
 		  ? &mips16_nop_insn					\
@@ -943,6 +946,9 @@ static bfd_boolean mips_fix_cn63xxp1;
 static bfd_boolean mips_fix_r5900;
 static bfd_boolean mips_fix_r5900_explicit;
 
+/* ...likewise -mfix-loongson3-llsc.  */
+static bfd_boolean mips_fix_loongson3_llsc = DEFAULT_MIPS_FIX_LOONGSON3_LLSC;
+
 /* We don't relax branches by default, since this causes us to expand
    `la .l2 - .l1' if there's a branch between .l1 and .l2, because we
    fail to compute the offset before expanding the macro to the most
@@ -1482,6 +1488,8 @@ enum options
     OPTION_NO_FIX_24K,
     OPTION_FIX_RM7000,
     OPTION_NO_FIX_RM7000,
+    OPTION_FIX_LOONGSON3_LLSC,
+    OPTION_NO_FIX_LOONGSON3_LLSC,
     OPTION_FIX_LOONGSON2F_JUMP,
     OPTION_NO_FIX_LOONGSON2F_JUMP,
     OPTION_FIX_LOONGSON2F_NOP,
@@ -1628,6 +1636,8 @@ struct option md_longopts[] =
   {"mfix7000", no_argument, NULL, OPTION_M7000_HILO_FIX},
   {"no-fix-7000", no_argument, NULL, OPTION_MNO_7000_HILO_FIX},
   {"mno-fix7000", no_argument, NULL, OPTION_MNO_7000_HILO_FIX},
+  {"mfix-loongson3-llsc",   no_argument, NULL, OPTION_FIX_LOONGSON3_LLSC},
+  {"mno-fix-loongson3-llsc", no_argument, NULL, OPTION_NO_FIX_LOONGSON3_LLSC},
   {"mfix-loongson2f-jump", no_argument, NULL, OPTION_FIX_LOONGSON2F_JUMP},
   {"mno-fix-loongson2f-jump", no_argument, NULL, OPTION_NO_FIX_LOONGSON2F_JUMP},
   {"mfix-loongson2f-nop", no_argument, NULL, OPTION_FIX_LOONGSON2F_NOP},
@@ -3678,6 +3688,10 @@ md_begin (void)
 		nop_insn.insn_opcode = LOONGSON2F_NOP_INSN;
 	      nop_insn.fixed_p = 1;
 	    }
+          if (sync_insn.insn_mo == NULL && strcmp (name, "sync") == 0)
+            {
+              create_insn (&sync_insn, mips_opcodes + i);
+            }
 	  ++i;
 	}
       while ((i < NUMOPCODES) && !strcmp (mips_opcodes[i].name, name));
@@ -6859,6 +6873,22 @@ fix_loongson2f (struct mips_cl_insn * ip)
     fix_loongson2f_jump (ip);
 }
 
+/* Fix loongson3 llsc errata: Insert sync before ll/lld. */
+static void
+fix_loongson3_llsc (struct mips_cl_insn * ip)
+{
+  gas_assert (!HAVE_CODE_COMPRESSION);
+
+  /* Skip if there is a sync before ll/lld.  */
+  if ((strcmp (ip->insn_mo->name, "ll") == 0
+       || strcmp (ip->insn_mo->name, "lld") == 0)
+      && (strcmp (history[0].insn_mo->name, "sync") != 0))
+    {
+      add_fixed_insn (&sync_insn);
+      insert_into_history (0, 1, &sync_insn);
+    }
+}
+
 /* IP is a branch that has a delay slot, and we need to fill it
    automatically.   Return true if we can do that by swapping IP
    with the previous instruction.
@@ -7316,6 +7346,9 @@ append_insn (struct mips_cl_insn *ip, expressionS *address_expr,
   if (mips_fix_loongson2f && !HAVE_CODE_COMPRESSION)
     fix_loongson2f (ip);
 
+  if (mips_fix_loongson3_llsc && !HAVE_CODE_COMPRESSION)
+    fix_loongson3_llsc (ip);
+
   file_ase_mips16 |= mips_opts.mips16;
   file_ase_micromips |= mips_opts.micromips;
 
@@ -14731,6 +14764,14 @@ md_parse_option (int c, const char *arg)
       mips_fix_rm7000 = 0;
       break;
 
+    case OPTION_FIX_LOONGSON3_LLSC:
+      mips_fix_loongson3_llsc = TRUE;
+      break;
+
+    case OPTION_NO_FIX_LOONGSON3_LLSC:
+      mips_fix_loongson3_llsc = FALSE;
+      break;
+
     case OPTION_FIX_LOONGSON2F_JUMP:
       mips_fix_loongson2f_jump = TRUE;
       break;
@@ -20140,9 +20181,20 @@ MIPS options:\n\
   fprintf (stream, _("\
 -minsn32		only generate 32-bit microMIPS instructions\n\
 -mno-insn32		generate all microMIPS instructions\n"));
+#if DEFAULT_MIPS_FIX_LOONGSON3_LLSC
+  fprintf (stream, _("\
+-mfix-loongson3-llsc	work around Loongson3 LL/SC errata, default\n\
+-mno-fix-loongson3-llsc	disable work around Loongson3 LL/SC errata\n"));
+#else
+  fprintf (stream, _("\
+-mfix-loongson3-llsc	work around Loongson3 LL/SC errata\n\
+-mno-fix-loongson3-llsc	disable work around Loongson3 LL/SC errata, default\n"));
+#endif
   fprintf (stream, _("\
 -mfix-loongson2f-jump	work around Loongson2F JUMP instructions\n\
 -mfix-loongson2f-nop	work around Loongson2F NOP errata\n\
+-mfix-loongson3-llsc	work around Loongson3 LL/SC errata\n\
+-mno-fix-loongson3-llsc	disable work around Loongson3 LL/SC errata\n\
 -mfix-vr4120		work around certain VR4120 errata\n\
 -mfix-vr4130		work around VR4130 mflo/mfhi errata\n\
 -mfix-24k		insert a nop after ERET and DERET instructions\n\
diff --git a/gas/configure b/gas/configure
index 27b6e8e8..13732153 100755
--- a/gas/configure
+++ b/gas/configure
@@ -809,6 +809,7 @@ enable_x86_relax_relocations
 enable_elf_stt_common
 enable_generate_build_notes
 enable_x86_used_note
+enable_mips_fix_loongson3_llsc
 enable_werror
 enable_build_warnings
 with_cpu
@@ -1471,6 +1472,8 @@ Optional Features:
                           generate GNU Build notes if none are provided by the
                           input
   --enable-x86-used-note  generate GNU x86 used ISA and feature properties
+  --enable-mips-fix-loongson3-llsc
+                          enable MIPS fix Loongson3 LLSC errata
   --enable-werror         treat compile warnings as errors
   --enable-build-warnings enable build-time compiler warnings
   --disable-nls           do not use Native Language Support
@@ -12125,6 +12128,17 @@ if test "${enable_x86_used_note+set}" = set; then :
 esac
 fi
 
+# Decide if the MIPS assembler should default to enable MIPS fix Loongson3
+# LLSC errata.
+ac_default_mips_fix_loongson3_llsc=unset
+# Provide a configuration option to override the default.
+# Check whether --enable-mips-fix-loongson3-llsc was given.
+if test "${enable_mips_fix_loongson3_llsc+set}" = set; then :
+  enableval=$enable_mips_fix_loongson3_llsc; case "${enableval}" in
+  yes)  ac_default_mips_fix_loongson3_llsc=1 ;;
+  no)   ac_default_mips_fix_loongson3_llsc=0 ;;
+esac
+fi
 
 using_cgen=no
 
@@ -13102,6 +13116,15 @@ cat >>confdefs.h <<_ACEOF
 _ACEOF
 
 
+if test ${ac_default_mips_fix_loongson3_llsc} = unset; then
+  ac_default_mips_fix_loongson3_llsc=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define DEFAULT_MIPS_FIX_LOONGSON3_LLSC $ac_default_mips_fix_loongson3_llsc
+_ACEOF
+
+
 if test x$ac_default_compressed_debug_sections = xyes ; then
 
 $as_echo "#define DEFAULT_FLAG_COMPRESS_DEBUG 1" >>confdefs.h
diff --git a/gas/configure.ac b/gas/configure.ac
index 93faa411..329ce079 100644
--- a/gas/configure.ac
+++ b/gas/configure.ac
@@ -125,6 +125,17 @@ AC_ARG_ENABLE(x86-used-note,
   no)   ac_default_generate_x86_used_note=0 ;;
 esac])dnl
 
+# Decide if the MIPS assembler should default to enable MIPS fix Loongson3
+# LLSC errata.
+ac_default_mips_fix_loongson3_llsc=unset
+# Provide a configuration option to override the default.
+AC_ARG_ENABLE(mips-fix-loongson3-llsc,
+             AS_HELP_STRING([--enable-mips-fix-loongson3-llsc],
+             [enable MIPS fix Loongson3 LLSC errata]),
+[case "${enableval}" in
+  yes)  ac_default_mips_fix_loongson3_llsc=1 ;;
+  no)   ac_default_mips_fix_loongson3_llsc=0 ;;
+esac])dnl
 
 using_cgen=no
 
@@ -663,6 +674,13 @@ AC_DEFINE_UNQUOTED(DEFAULT_X86_USED_NOTE,
   [Define to 1 if you want to generate GNU x86 used ISA and feature
    properties by default.])
 
+if test ${ac_default_mips_fix_loongson3_llsc} = unset; then
+  ac_default_mips_fix_loongson3_llsc=0
+fi
+AC_DEFINE_UNQUOTED(DEFAULT_MIPS_FIX_LOONGSON3_LLSC,
+  $ac_default_mips_fix_loongson3_llsc,
+  [Define to 1 if you want to fix Loongson3 LLSC Errata by default.])
+
 if test x$ac_default_compressed_debug_sections = xyes ; then
   AC_DEFINE(DEFAULT_FLAG_COMPRESS_DEBUG, 1, [Define if you want compressed debug sections by default.])
 fi
diff --git a/gas/doc/c-mips.texi b/gas/doc/c-mips.texi
index 76dfb107..b5aa5781 100644
--- a/gas/doc/c-mips.texi
+++ b/gas/doc/c-mips.texi
@@ -308,6 +308,13 @@ Replace nops by @code{or at,at,zero} to work around the Loongson2F
 deadlock.  The issue has been solved in later Loongson2F batches, but
 this fix has no side effect to them.
 
+@item -mfix-loongson3-llsc
+@itemx -mno-fix-loongson3-llsc
+Insert @samp{sync} before @samp{ll} and @samp{lld} to work around
+Loongson3 LLSC errata.  Without it, under extrame cases, the CPU might
+deadlock. The default can be controlled by the
+@option{--enable-mips-fix-loongson3-llsc=[yes|no]} configure option.
+
 @item -mfix-vr4120
 @itemx -mno-fix-vr4120
 Insert nops to work around certain VR4120 errata.  This option is
-- 
2.20.0.rc2


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