[PATCH] LoongArch: adjust the default of -mexplicit-relocs by checking gas feature

[Xi Ruoyao <xry111@xry111.site>]

> > Maybe we can add a check in gcc/configure.ac to see if gcc_cv_ld
> > supports %got_pc_hi20 and adjust the default for -m[no]-explicit-relocs?

> I think this is a good way, I'll look at adding a check.

The following should work.  I've tested it locally by building GCC with
both old (2.38 with patch) and new (trunk) Binutils. Ok for trunk?

I simply checked as instead of ld.  If as supports explicitly
relocations, the produced .o file won't be supported by an old ld even
if we use -mno-explicit-relocs (because as will generate new relocation
types for la.local etc).  So such a mismatch between as and ld can be
considered "completely broken" and we don't need to support it.  And,
the Alpha port also check the assembler for the default of -mexplicit-
relocs.

This should be documented in invoke.texi, but currently it does not
mention -mexplicit-relocs for LoongArch at all.  So I'll submit the
doclater in another patch.

-- >8 --

The assembly produced with -mexplicit-relocs is not supported by gas <=
2.39.  Check if the assembler supports explicit relocations and set the
default accordingly.

gcc/ChangeLog:

	* configure.ac (HAVE_AS_EXPLICIT_RELOCS): Define to 1 if the
	assembler supports explicit relocation for LoongArch.
	* configure: Regenerate.
	* config/loongarch/loongarch-opts.h (HAVE_AS_EXPLICIT_RELOCS):
	Define to 0 if not defined.
	* config/loongarch/genopts/loongarch.opt.in
	(TARGET_EXPLICIT_RELOCS): Default to HAVE_AS_EXPLICIT_RELOCS.
	* config/loongarch/loongarch.opt: Regenerate.
---
 gcc/config/loongarch/genopts/loongarch.opt.in |  2 +-
 gcc/config/loongarch/loongarch-opts.h         |  4 ++
 gcc/config/loongarch/loongarch.opt            |  2 +-
 gcc/configure                                 | 37 +++++++++++++++++--
 gcc/configure.ac                              |  7 +++-
 5 files changed, 46 insertions(+), 6 deletions(-)

diff --git a/gcc/config/loongarch/genopts/loongarch.opt.in b/gcc/config/loongarch/genopts/loongarch.opt.in
index 6f39500935d..a571b6b7524 100644
--- a/gcc/config/loongarch/genopts/loongarch.opt.in
+++ b/gcc/config/loongarch/genopts/loongarch.opt.in
@@ -155,7 +155,7 @@ Target Joined RejectNegative UInteger Var(loongarch_max_inline_memcpy_size) Init
 -mmax-inline-memcpy-size=SIZE	Set the max size of memcpy to inline, default is 1024.
 
 mexplicit-relocs
-Target Var(TARGET_EXPLICIT_RELOCS) Init(1)
+Target Var(TARGET_EXPLICIT_RELOCS) Init(HAVE_AS_EXPLICIT_RELOCS)
 Use %reloc() assembly operators.
 
 ; The code model option names for -mcmodel.
diff --git a/gcc/config/loongarch/loongarch-opts.h b/gcc/config/loongarch/loongarch-opts.h
index eaa6fc07448..da24ecd2b50 100644
--- a/gcc/config/loongarch/loongarch-opts.h
+++ b/gcc/config/loongarch/loongarch-opts.h
@@ -87,4 +87,8 @@ loongarch_config_target (struct loongarch_target *target,
    while -m[no]-memcpy imposes a global constraint.  */
 #define TARGET_DO_OPTIMIZE_BLOCK_MOVE_P  loongarch_do_optimize_block_move_p()
 
+#ifndef HAVE_AS_EXPLICIT_RELOCS
+#define HAVE_AS_EXPLICIT_RELOCS 0
+#endif
+
 #endif /* LOONGARCH_OPTS_H */
diff --git a/gcc/config/loongarch/loongarch.opt b/gcc/config/loongarch/loongarch.opt
index 7a8c5b44418..9df7e187283 100644
--- a/gcc/config/loongarch/loongarch.opt
+++ b/gcc/config/loongarch/loongarch.opt
@@ -162,7 +162,7 @@ Target Joined RejectNegative UInteger Var(loongarch_max_inline_memcpy_size) Init
 -mmax-inline-memcpy-size=SIZE	Set the max size of memcpy to inline, default is 1024.
 
 mexplicit-relocs
-Target Var(TARGET_EXPLICIT_RELOCS) Init(1)
+Target Var(TARGET_EXPLICIT_RELOCS) Init(HAVE_AS_EXPLICIT_RELOCS)
 Use %reloc() assembly operators.
 
 ; The code model option names for -mcmodel.
diff --git a/gcc/configure b/gcc/configure
index 62872d132ea..7eb9479ae8e 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -19674,7 +19674,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 19679 "configure"
+#line 19677 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -19780,7 +19780,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 19785 "configure"
+#line 19783 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -28771,7 +28771,7 @@ $as_echo "#define HAVE_AS_MARCH_ZIFENCEI 1" >>confdefs.h
 fi
 
     ;;
-  loongarch*-*-*)
+    loongarch*-*-*)
     { $as_echo "$as_me:${as_lineno-$LINENO}: checking assembler for .dtprelword support" >&5
 $as_echo_n "checking assembler for .dtprelword support... " >&6; }
 if ${gcc_cv_as_loongarch_dtprelword+:} false; then :
@@ -28807,6 +28807,37 @@ if test $gcc_cv_as_loongarch_dtprelword != yes; then
 $as_echo "#define HAVE_AS_DTPRELWORD 1" >>confdefs.h
 
 fi
+    { $as_echo "$as_me:${as_lineno-$LINENO}: checking assembler for explicit relocation support" >&5
+$as_echo_n "checking assembler for explicit relocation support... " >&6; }
+if ${gcc_cv_as_loongarch_explicit_relocs+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  gcc_cv_as_loongarch_explicit_relocs=no
+  if test x$gcc_cv_as != x; then
+    $as_echo 'a:pcalau12i $t0,%pc_hi20(a)' > conftest.s
+    if { ac_try='$gcc_cv_as $gcc_cv_as_flags  -o conftest.o conftest.s >&5'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; }
+    then
+	gcc_cv_as_loongarch_explicit_relocs=yes
+    else
+      echo "configure: failed program was" >&5
+      cat conftest.s >&5
+    fi
+    rm -f conftest.o conftest.s
+  fi
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $gcc_cv_as_loongarch_explicit_relocs" >&5
+$as_echo "$gcc_cv_as_loongarch_explicit_relocs" >&6; }
+if test $gcc_cv_as_loongarch_explicit_relocs = yes; then
+
+$as_echo "#define HAVE_AS_EXPLICIT_RELOCS 1" >>confdefs.h
+
+fi
+
     ;;
     s390*-*-*)
     { $as_echo "$as_me:${as_lineno-$LINENO}: checking assembler for .gnu_attribute support" >&5
diff --git a/gcc/configure.ac b/gcc/configure.ac
index 446747311a6..e5f708c6b38 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -5287,7 +5287,7 @@ configured with --enable-newlib-nano-formatted-io.])
       [AC_DEFINE(HAVE_AS_MARCH_ZIFENCEI, 1,
 		 [Define if the assembler understands -march=rv*_zifencei.])])
     ;;
-  loongarch*-*-*)
+    loongarch*-*-*)
     gcc_GAS_CHECK_FEATURE([.dtprelword support],
       gcc_cv_as_loongarch_dtprelword, [2,18,0],,
       [.section .tdata,"awT",@progbits
@@ -5297,6 +5297,11 @@ x:
 	.dtprelword x+0x8000],,
       [AC_DEFINE(HAVE_AS_DTPRELWORD, 1,
 	  [Define if your assembler supports .dtprelword.])])
+    gcc_GAS_CHECK_FEATURE([explicit relocation support],
+      gcc_cv_as_loongarch_explicit_relocs,,
+      [a:pcalau12i $t0,%pc_hi20(a)],,
+      [AC_DEFINE(HAVE_AS_EXPLICIT_RELOCS, 1,
+	  [Define if your assembler supports explicit relocation.])])
     ;;
     s390*-*-*)
     gcc_GAS_CHECK_FEATURE([.gnu_attribute support],
-- 
2.37.1