[PATCH v2, rs6000] Enable absolute jump table for PPC AIX and Linux

[HAO CHEN GUI via Gcc-patches]

Hi,
   This patch enables absolute jump tables on PPC AIX and Linux. For AIX, the 
jump
table is placed in data section. For Linux, it is placed in RELRO section when
relocation is needed.

   Bootstrapped and tested on AIX,Linux BE and LE with no regressions. Is this 
okay for trunk?
Any recommendations? Thanks a lot.

ChangeLog
2022-02-16 Haochen Gui <guih...@linux.ibm.com>

gcc/
        * config/rs6000/aix.h (JUMP_TABLES_IN_TEXT_SECTION): Define.
        * config/rs6000/linux64.h (JUMP_TABLES_IN_TEXT_SECTION): Likewise.
        * config/rs6000/rs6000.cc (rs6000_option_override_internal): Enable
        absolute jump tables for AIX and Linux.
        (rs6000_xcoff_function_rodata_section): Implement.
        * config/rs6000/xcoff.h (TARGET_ASM_FUNCTION_RODATA_SECTION): Define.

patch.diff
diff --git a/gcc/config/rs6000/aix.h b/gcc/config/rs6000/aix.h
index ad3238bf09a..b52208c2ee7 100644
--- a/gcc/config/rs6000/aix.h
+++ b/gcc/config/rs6000/aix.h
@@ -253,7 +253,7 @@

 /* Indicate that jump tables go in the text section.  */

-#define JUMP_TABLES_IN_TEXT_SECTION 1
+#define JUMP_TABLES_IN_TEXT_SECTION 0

 /* Define any extra SPECS that the compiler needs to generate.  */
 #undef  SUBTARGET_EXTRA_SPECS
diff --git a/gcc/config/rs6000/linux64.h b/gcc/config/rs6000/linux64.h
index b2a7afabc73..16df9ef167f 100644
--- a/gcc/config/rs6000/linux64.h
+++ b/gcc/config/rs6000/linux64.h
@@ -239,7 +239,7 @@ extern int dot_symbols;

 /* Indicate that jump tables go in the text section.  */
 #undef  JUMP_TABLES_IN_TEXT_SECTION
-#define JUMP_TABLES_IN_TEXT_SECTION TARGET_64BIT
+#define JUMP_TABLES_IN_TEXT_SECTION 0

 /* The linux ppc64 ABI isn't explicit on whether aggregates smaller
    than a doubleword should be padded upward or downward.  You could
diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index bc3ef0721a4..e9c5552c082 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -4954,6 +4954,10 @@ rs6000_option_override_internal (bool global_init_p)
     warning (0, "%qs is deprecated and not recommended in any circumstances",
             "-mno-speculate-indirect-jumps");

+  /* Enable absolute jump tables for AIX and Linux.  */
+  if (DEFAULT_ABI == ABI_AIX || DEFAULT_ABI == ABI_ELFv2)
+    rs6000_relative_jumptables = 0;
+
   return ret;
 }

@@ -28751,6 +28755,15 @@ constant_generates_xxspltidp (vec_const_128bit_type 
*vsx_const)
   return sf_value;
 }

+section * rs6000_xcoff_function_rodata_section (tree decl ATTRIBUTE_UNUSED,
+                                               bool relocatable)
+{
+  if (relocatable)
+    return data_section;
+  else
+    return readonly_data_section;
+}
+
 
 struct gcc_target targetm = TARGET_INITIALIZER;

diff --git a/gcc/config/rs6000/xcoff.h b/gcc/config/rs6000/xcoff.h
index cd0f99cb9c6..0dacd86eed9 100644
--- a/gcc/config/rs6000/xcoff.h
+++ b/gcc/config/rs6000/xcoff.h
@@ -98,7 +98,7 @@
 #define TARGET_ASM_SELECT_SECTION  rs6000_xcoff_select_section
 #define TARGET_ASM_SELECT_RTX_SECTION  rs6000_xcoff_select_rtx_section
 #define TARGET_ASM_UNIQUE_SECTION  rs6000_xcoff_unique_section
-#define TARGET_ASM_FUNCTION_RODATA_SECTION default_no_function_rodata_section
+#define TARGET_ASM_FUNCTION_RODATA_SECTION rs6000_xcoff_function_rodata_section
 #define TARGET_STRIP_NAME_ENCODING  rs6000_xcoff_strip_name_encoding
 #define TARGET_SECTION_TYPE_FLAGS  rs6000_xcoff_section_type_flags
 #ifdef HAVE_AS_TLS