i386: Access external function via GOT slot for -fno-plthjl/no-plt/got32x

i386 psABI has been updated to clarify that R_386_GOT32X and R_386_GOT32
relocations can be used to access GOT without base register when PIC is
disabled:

https://groups.google.com/forum/#!topic/ia32-abi/awsRSvJOJfs

32-bit x86 assembler and linker from binutils 2.26.1 and 2.27 support

call/jmp *_start@GOT
cmpl $0, bar@GOT

for both normal and IFUNC functions.  We check if 32-bit x86 assembler
and linker have the fix for:

https://sourceware.org/bugzilla/show_bug.cgi?id=20244

before accessing external function via GOT slot for -fno-plt in both PIC
and non-PIC modes.

	PR target/66232
	PR target/67400
	* configure.ac (as_ix86_tls_ldm_opt): Renamed to ...
	(as_ix86_gas_32_opt): This.
	(ld_ix86_tls_ldm_opt): Renamed to ...
	(ld_ix86_gld_32_opt): This.
	(R_386_TLS_LDM reloc): Updated.
	(R_386_GOT32X reloc): New assembler/linker check.
	(HAVE_AS_IX86_GOT32X): New.  Defined to 1 if 32-bit assembler and
	linker support "jmp *_start@GOT" and "cmpl $0, bar@GOT".  Otherise,
	defined to 0.
	* config.in: Regenerated.
	* configure: Likewise.
	* config/i386/i386.c (ix86_force_load_from_GOT_p): Return
	true if HAVE_AS_IX86_GOT32X is 1 in 32-bit mode.
	(ix86_legitimate_address_p): Allow UNSPEC_GOT for -fno-plt
	if ix86_force_load_from_GOT_p returns true.
	(ix86_print_operand_address_as): Also support UNSPEC_GOT if
	ix86_force_load_from_GOT_p returns true.
	(ix86_expand_move): Generate UNSPEC_GOT in 32-bit mode to load
	the external function address via the GOT slot.
	(ix86_nopic_noplt_attribute_p): Check both TARGET_64BIT and
	HAVE_AS_IX86_GOT32X before returning false.
	(ix86_output_call_insn): Generate "%!jmp/call\t*%p0@GOT" in
	32-bit mode if ix86_nopic_noplt_attribute_p returns true.

gcc/testsuite/

	PR target/66232
	PR target/67400
	* gcc.target/i386/pr66232-14.c: New file.
	* gcc.target/i386/pr66232-15.c: Likewise.
	* gcc.target/i386/pr66232-16.c: Likewise.
	* gcc.target/i386/pr66232-17.c: Likewise.
	* gcc.target/i386/pr67400-1.c: Don't disable for ia32.  Scan for
	ia32 if R_386_GOT32X relocation is supported.
	* gcc.target/i386/pr67400-2.c: Likewise.
	* gcc.target/i386/pr67400-3.c: Likewise.
	* gcc.target/i386/pr67400-4.c: Likewise.
	* gcc.target/i386/pr67400-6.c: Likewise.
	* gcc.target/i386/pr67400-7.c: Likewise.
	* lib/target-supports.exp (check_effective_target_got32x_reloc):
	New.

1 files changed, 34 insertions, 5 deletions

diff --git a/gcc/configure.ac b/gcc/configure.ac
index fabd48e5a25..b0f38d1e430 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -4164,13 +4164,13 @@ tls_ld:
 
     # Enforce 32-bit output with gas and gld.
     if test x$gas = xyes; then
-      as_ix86_tls_ldm_opt="--32"
+      as_ix86_gas_32_opt="--32"
     fi
     if echo "$ld_ver" | grep GNU > /dev/null; then
       if $gcc_cv_ld -V 2>/dev/null | grep elf_i386_sol2 > /dev/null; then
-        ld_ix86_tls_ldm_opt="-melf_i386_sol2"
+        ld_ix86_gld_32_opt="-melf_i386_sol2"
       else
-        ld_ix86_tls_ldm_opt="-melf_i386"
+        ld_ix86_gld_32_opt="-melf_i386"
       fi
     fi
     conftest_s='
@@ -4186,10 +4186,10 @@ _start:
 value:'
     gcc_GAS_CHECK_FEATURE([R_386_TLS_LDM reloc],
         gcc_cv_as_ix86_tlsldm,,
-	[$as_ix86_tls_ldm_opt],
+	[$as_ix86_gas_32_opt],
 	[$conftest_s],
 	[if test x$gcc_cv_ld != x && test x$gcc_cv_objdump != x \
-	    && $gcc_cv_ld $ld_ix86_tls_ldm_opt -o conftest conftest.o $ld_tls_libs -lc > /dev/null 2>&1; then
+	    && $gcc_cv_ld $ld_ix86_gld_32_opt -o conftest conftest.o $ld_tls_libs -lc > /dev/null 2>&1; then
 	   if $gcc_cv_objdump -d conftest 2>/dev/null | grep nop > /dev/null \
 	      || dis conftest 2>/dev/null | grep nop > /dev/null; then
 	     gcc_cv_as_ix86_tlsldm=yes
@@ -4200,6 +4200,35 @@ value:'
       [`if test $gcc_cv_as_ix86_tlsldm = yes; then echo 1; else echo 0; fi`],
       [Define to 1 if your assembler and linker support @tlsldm.])
 
+    conftest_s='
+	.data
+bar:
+	.byte 1
+	.text
+	.global _start
+_start:
+	 cmpl $0, bar@GOT
+	 jmp *_start@GOT'
+    gcc_GAS_CHECK_FEATURE([R_386_GOT32X reloc],
+        gcc_cv_as_ix86_got32x,,
+	[$as_ix86_gas_32_opt],
+	[$conftest_s],
+	[if test x$gcc_cv_ld != x && test x$gcc_cv_objdump != x \
+	    && test x$gcc_cv_readelf != x \
+	    && $gcc_cv_readelf --relocs --wide conftest.o 2>&1 \
+	       | grep R_386_GOT32X > /dev/null 2>&1 \
+	    && $gcc_cv_ld $ld_ix86_gld_32_opt -o conftest conftest.o > /dev/null 2>&1; then
+	   if $gcc_cv_objdump -dw conftest 2>&1 \
+	      | grep 0xffffff > /dev/null 2>&1; then
+	     gcc_cv_as_ix86_got32x=no
+	   else
+	     gcc_cv_as_ix86_got32x=yes
+	   fi
+	 fi
+	 rm -f conftest])
+    AC_DEFINE_UNQUOTED(HAVE_AS_IX86_GOT32X,
+      [`if test x"$gcc_cv_as_ix86_got32x" = xyes; then echo 1; else echo 0; fi`],
+      [Define 0/1 if your assembler and linker support @GOT.])
     ;;
 
   ia64*-*-*)