Use the section flag 'o' for __patchable_function_entries

This commit in GNU binutils 2.35:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=b7d072167715829eed0622616f6ae0182900de3e

added the section flag 'o' to .section directive:

.section __patchable_function_entries,"awo",@progbits,foo

which specifies the symbol name which the section references.  Assembler
creates a unique __patchable_function_entries section with the section,
where foo is defined, as its linked-to section.  Linker keeps a section
if its linked-to section is kept during garbage collection.

This patch checks assembler support for the section flag 'o' and uses
it to implement __patchable_function_entries section.  Since Solaris may
use GNU assembler with Solairs ld.  Even if GNU assembler supports the
section flag 'o', it doesn't mean that Solairs ld supports it.  This
feature is disabled for Solairs targets.

gcc/

	PR middle-end/93195
	PR middle-end/93197
	* configure.ac (HAVE_GAS_SECTION_LINK_ORDER): New.  Define 1 if
	the assembler supports the section flag 'o' for specifying
	section with link-order.
	* output.h (SECTION_LINK_ORDER): New.  Defined to 0x8000000.
	(SECTION_MACH_DEP): Changed from 0x8000000 to 0x10000000.
	* targhooks.c (default_print_patchable_function_entry): Pass
	SECTION_LINK_ORDER to switch_to_section if the section flag 'o'
	works.  Pass current_function_decl to switch_to_section.
	* varasm.c (default_elf_asm_named_section): Use 'o' flag for
	SECTION_LINK_ORDER if assembler supports it.
	* config.in: Regenerated.
	* configure: Likewise.
	* doc/sourcebuild.texi: Document o_flag_in_section.

gcc/testsuite/

	PR middle-end/93195
	* g++.dg/pr93195a.C: New test.
	* g++.dg/pr93195b.C: Likewise.
	* lib/target-supports.exp
	(check_effective_target_o_flag_in_section): New proc.

gcc/config.in

@@ -1386,6 +1386,12 @@
 #endif
 
 
+/* Define 0/1 if your assembler supports 'o' flag in .section directive. */
+#ifndef USED_FOR_TARGET
+#undef HAVE_GAS_SECTION_LINK_ORDER
+#endif
+
+
 /* Define 0/1 if your assembler supports marking sections with SHF_GNU_RETAIN
    flag. */
 #ifndef USED_FOR_TARGET

gcc/configure

@@ -24481,6 +24481,58 @@ cat >>confdefs.h <<_ACEOF
 _ACEOF
 
 
+# Test if the assembler supports the section flag 'o' for specifying
+# section with link-order.
+case "${target}" in
+  # Solaris may use GNU assembler with Solairs ld.  Even if GNU
+  # assembler supports the section flag 'o', it doesn't mean that
+  # Solairs ld supports it.
+  *-*-solaris2*)
+    gcc_cv_as_section_link_order=no
+    ;;
+  *)
+    { $as_echo "$as_me:${as_lineno-$LINENO}: checking assembler for section 'o' flag" >&5
+$as_echo_n "checking assembler for section 'o' flag... " >&6; }
+if ${gcc_cv_as_section_link_order+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  gcc_cv_as_section_link_order=no
+    if test $in_tree_gas = yes; then
+    if test $gcc_cv_gas_vers -ge `expr \( \( 2 \* 1000 \) + 35 \) \* 1000 + 0`
+  then gcc_cv_as_section_link_order=yes
+fi
+  elif test x$gcc_cv_as != x; then
+    $as_echo '.section .foo,"a"
+.byte 0
+.section __patchable_function_entries,"awo",%progbits,.foo
+.byte 0' > conftest.s
+    if { ac_try='$gcc_cv_as $gcc_cv_as_flags --fatal-warnings -o conftest.o conftest.s >&5'
+  { { eval echo "\"\$as_me\":${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_section_link_order=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: $gcc_cv_as_section_link_order" >&5
+$as_echo "$gcc_cv_as_section_link_order" >&6; }
+
+
+    ;;
+esac
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_GAS_SECTION_LINK_ORDER `if test $gcc_cv_as_section_link_order = yes; then echo 1; else echo 0; fi`
+_ACEOF
+
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking assembler for section merging support" >&5
 $as_echo_n "checking assembler for section merging support... " >&6; }
 if ${gcc_cv_as_shf_merge+:} false; then :

gcc/configure.ac

@@ -3350,6 +3350,28 @@ AC_DEFINE_UNQUOTED(HAVE_GAS_SHF_GNU_RETAIN,
   [`if test $gcc_cv_as_shf_gnu_retain = yes; then echo 1; else echo 0; fi`],
   [Define 0/1 if your assembler supports marking sections with SHF_GNU_RETAIN flag.])
 
+# Test if the assembler supports the section flag 'o' for specifying
+# section with link-order.
+case "${target}" in
+  # Solaris may use GNU assembler with Solairs ld.  Even if GNU
+  # assembler supports the section flag 'o', it doesn't mean that
+  # Solairs ld supports it.
+  *-*-solaris2*)
+    gcc_cv_as_section_link_order=no
+    ;;
+  *)
+    gcc_GAS_CHECK_FEATURE([section 'o' flag], gcc_cv_as_section_link_order,
+      [2,35,0], [--fatal-warnings],
+      [.section .foo,"a"
+.byte 0
+.section __patchable_function_entries,"awo",%progbits,.foo
+.byte 0])
+    ;;
+esac
+AC_DEFINE_UNQUOTED(HAVE_GAS_SECTION_LINK_ORDER,
+  [`if test $gcc_cv_as_section_link_order = yes; then echo 1; else echo 0; fi`],
+  [Define 0/1 if your assembler supports 'o' flag in .section directive.])
+
 gcc_GAS_CHECK_FEATURE(section merging support, gcc_cv_as_shf_merge,
  [elf,2,12,0], [--fatal-warnings],
  [.section .rodata.str, "aMS", @progbits, 1])

gcc/doc/sourcebuild.texi

@@ -2548,6 +2548,9 @@ Target supports the @code{noinit} variable attribute.
 @item nonpic
 Target does not generate PIC by default.
 
+@item o_flag_in_section
+Target supports the 'o' flag in .section directive in assembly inputs.
+
 @item offload_gcn
 Target has been configured for OpenACC/OpenMP offloading on AMD GCN.
 

gcc/output.h

@@ -382,10 +382,11 @@ extern void no_asm_to_stream (FILE *);
 #define SECTION_RELRO	 0x1000000	/* data is readonly after relocation processing */
 #define SECTION_EXCLUDE  0x2000000	/* discarded by the linker */
 #define SECTION_RETAIN	 0x4000000	/* retained by the linker.  */
+#define SECTION_LINK_ORDER 0x8000000	/* section needs link-order.  */
 
 /* NB: The maximum SECTION_MACH_DEP is 0x10000000 since AVR needs 4 bits
    in SECTION_MACH_DEP.  */
-#define SECTION_MACH_DEP 0x8000000	/* subsequent bits reserved for target */
+#define SECTION_MACH_DEP 0x10000000	/* subsequent bits reserved for target */
 
 /* This SECTION_STYLE is used for unnamed sections that we can switch
    to using a special assembler directive.  */

gcc/targhooks.c

@@ -1864,8 +1864,11 @@ default_print_patchable_function_entry (FILE *file,
       patch_area_number++;
       ASM_GENERATE_INTERNAL_LABEL (buf, "LPFE", patch_area_number);
 
+      unsigned int flags = SECTION_WRITE | SECTION_RELRO;
+      if (HAVE_GAS_SECTION_LINK_ORDER)
+	flags |= SECTION_LINK_ORDER;
       switch_to_section (get_section ("__patchable_function_entries",
-				      SECTION_WRITE | SECTION_RELRO, NULL));
+				      flags, current_function_decl));
       assemble_align (POINTER_SIZE);
       fputs (asm_op, file);
       assemble_name_raw (file, buf);

gcc/testsuite/g++.dg/pr93195a.C

@@ -0,0 +1,27 @@
+/* { dg-do link { target { ! { nvptx*-*-* visium-*-* } } } } */
+// { dg-require-effective-target o_flag_in_section }
+/* { dg-options "-O0 -fpatchable-function-entry=1" } */
+/* { dg-additional-options "-fno-pie" { target sparc*-*-* } } */
+/* { dg-additional-sources pr93195b.C } */
+
+extern void bar1 (void);
+
+inline void
+foo (void)
+{
+}
+
+void
+bar (void)
+{
+  foo ();
+  bar1 ();
+}
+
+int
+main ()
+{
+  bar ();
+  return 0;
+}
+

gcc/testsuite/g++.dg/pr93195b.C

@@ -0,0 +1,14 @@
+/* { dg-do compile { target { ! { nvptx*-*-* visium-*-* } } } } */
+/* { dg-options "-O0 -fpatchable-function-entry=1" } */
+/* { dg-additional-options "-fno-pie" { target sparc*-*-* } } */
+
+inline void
+foo (void)
+{
+}
+
+void
+bar1 (void)
+{
+  foo ();
+}

gcc/testsuite/lib/target-supports.exp

@@ -10702,3 +10702,43 @@ proc check_effective_target_R_flag_in_section { } {
 	}
     }]
 }
+
+# Return 1 if this target supports 'o' flag in .section directive, 0
+# otherwise.  Cache the result.
+
+proc check_effective_target_o_flag_in_section { } {
+    global tool
+    global GCC_UNDER_TEST
+
+    # Need auto-host.h to check linker support.
+    if { ![file exists ../../auto-host.h ] } {
+	return 0
+    }
+
+    return [check_cached_effective_target o_flag_in_section {
+
+	set src pie[pid].c
+	set obj pie[pid].o
+
+	set f [open $src "w"]
+	puts $f "#include \"../../auto-host.h\""
+	puts $f "#if HAVE_GAS_SECTION_LINK_ORDER == 0"
+	puts $f "# error Assembler does not support 'o' flag in .section directive."
+	puts $f "#endif"
+	close $f
+
+	verbose "check_effective_target_o_flag_in_section compiling testfile $src" 2
+	set lines [${tool}_target_compile $src $obj object ""]
+
+	file delete $src
+	file delete $obj
+
+	if [string match "" $lines] then {
+	    verbose "check_effective_target_o_flag_in_section testfile compilation passed" 2
+	    return 1
+	} else {
+	    verbose "check_effective_target_o_flag_in_section testfile compilation failed" 2
+	    return 0
+	}
+    }]
+}

gcc/varasm.c

@@ -6789,6 +6789,8 @@ default_elf_asm_named_section (const char *name, unsigned int flags,
 	*f++ = 'G';
       if (flags & SECTION_RETAIN)
 	*f++ = 'R';
+      if (flags & SECTION_LINK_ORDER)
+	*f++ = 'o';
 #ifdef MACH_DEP_SECTION_ASM_FLAG
       if (flags & SECTION_MACH_DEP)
 	*f++ = MACH_DEP_SECTION_ASM_FLAG;
@@ -6821,6 +6823,14 @@ default_elf_asm_named_section (const char *name, unsigned int flags,
 
       if (flags & SECTION_ENTSIZE)
 	fprintf (asm_out_file, ",%d", flags & SECTION_ENTSIZE);
+      if (flags & SECTION_LINK_ORDER)
+	{
+	  tree id = DECL_ASSEMBLER_NAME (decl);
+	  ultimate_transparent_alias_target (&id);
+	  const char *name = IDENTIFIER_POINTER (id);
+	  name = targetm.strip_name_encoding (name);
+	  fprintf (asm_out_file, ",%s", name);
+	}
       if (HAVE_COMDAT_GROUP && (flags & SECTION_LINKONCE))
 	{
 	  if (TREE_CODE (decl) == IDENTIFIER_NODE)