[PATCH] Add support for putting jump table into relocation read-only section

HAO CHEN GUI guihaoc@linux.ibm.com
Fri Aug 14 07:20:03 GMT 2020


This patch adds a section selection for jump tables. The jump tables can 
be put into read-only data section or relocation read-only data section 
by the relocation flags. When the PIC flag is set and jump table is 
non-relative, the jump table is put into relocation read-only section.

section *
select_jump_table_section (tree decl)
   int reloc;
   bool section_reloc;

   reloc = (! CASE_VECTOR_PC_RELATIVE && flag_pic &&
            ! targetm.asm_out.generate_pic_addr_diff_vec ()) ? 1 : 0;

   section_reloc = (reloc & targetm.asm_out.reloc_rw_mask ());
   return targetm.asm_out.function_rodata_section (decl, section_reloc);

The attachments are the patch diff file and change log file.

Bootstrapped and tested on powerpc64le-linux-gnu with no regressions.  
Is this okay for trunk? Any recommendations? Thanks a lot.

-------------- next part --------------
        * final.c (select_jump_table_section): Implement a function to select 
		the section of jump tables by reloc_rw_mask and other flags.
		* output.h (default_function_rodata_section, default_no_function_rodata_section):
		Add the second argument to the declarations.
        * target.def (function_rodata_section): Change the doc and add the second argument.
		* doc/tm.texi: Regenerate.
        * varasm.c (default_function_rodata_section, default_no_function_rodata_section, 
		function_mergeable_rodata_prefix): Add the second argument in default_function_rodata_section.
		It indicates the section should be read-only or relocation read-only.
		Add the second argument in default_function_rodata_section. Set the second argument to
		false when default_function_rodata_section calls function_rodata_section.
		* config/mips/mips.c (mips_function_rodata_section): Add the second arugment and set it
		to false when it calls function_rodata_section.
		* config/s390/s390.c (targetm.asm_out.function_rodata_section): 
		Set the second argument to false.
		* config/s390/s390.md Likewise.
-------------- next part --------------
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 6e7d9dc54a9..3ff7527f2cc 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -7712,6 +7712,15 @@ if function is in @code{.text.name}, and the normal readonly-data section
 @end deftypefn
+@deftypefn {Target Hook} {section *} TARGET_ASM_FUNCTION_RELRO_SECTION (tree @var{decl})
+Return the relro section associated with
+@samp{DECL_SECTION_NAME (@var{decl})}.
+The default version of this function selects @code{.gnu.linkonce.r.name} if
+the function's section is @code{.gnu.linkonce.t.name}, 
+@code{.data.rel.ro.name} if function is in @code{.text.name}, 
+and the normal data relro section otherwise.
+@end deftypefn
 @deftypevr {Target Hook} {const char *} TARGET_ASM_MERGEABLE_RODATA_PREFIX
 Usually, the compiler uses the prefix @code{".rodata"} to construct
 section names for mergeable constant data.  Define this macro to override
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index 3be984bbd5c..0ac1488c837 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -5007,6 +5007,8 @@ it is unlikely to be called.
diff --git a/gcc/final.c b/gcc/final.c
index a3601964a8d..ba198182663 100644
--- a/gcc/final.c
+++ b/gcc/final.c
@@ -107,6 +107,10 @@ along with GCC; see the file COPYING3.  If not see
 /* Bitflags used by final_scan_insn.  */
 #define SEEN_NOTE	1
 #define SEEN_EMITTED	2
@@ -2154,6 +2158,23 @@ asm_show_source (const char *filename, int linenum)
   fputc ('\n', asm_out_file);
+/* Select sections for jump table.
+   If the jump table need to be relocated, 
+   select relro sections. Otherwise in readonly section */
+section *
+select_jump_table_section (tree decl)
+  int relco;
+  if (relco & targetm.asm_out.reloc_rw_mask ())
+    return targetm.asm_out.function_relro_section (decl);
+  else 
+    return targetm.asm_out.function_rodata_section (decl);
 /* The final scan for one insn, INSN.
    Args are same as in `final', except that INSN
    is the insn being scanned.
@@ -2492,7 +2513,7 @@ final_scan_insn_1 (rtx_insn *insn, FILE *file, int optimize_p ATTRIBUTE_UNUSED,
 	      int log_align;
-	      switch_to_section (targetm.asm_out.function_rodata_section
+	      switch_to_section (select_jump_table_section
@@ -2571,7 +2592,7 @@ final_scan_insn_1 (rtx_insn *insn, FILE *file, int optimize_p ATTRIBUTE_UNUSED,
-	      switch_to_section (targetm.asm_out.function_rodata_section
+	      switch_to_section (select_jump_table_section
 	      switch_to_section (current_function_section ());
diff --git a/gcc/output.h b/gcc/output.h
index eb253c50329..9a463c42955 100644
--- a/gcc/output.h
+++ b/gcc/output.h
@@ -573,6 +573,7 @@ extern section *default_elf_select_section (tree, int, unsigned HOST_WIDE_INT);
 extern void default_unique_section (tree, int);
 extern section *default_function_rodata_section (tree);
 extern section *default_no_function_rodata_section (tree);
+extern section *default_function_relro_section (tree);
 extern section *default_clone_table_section (void);
 extern section *default_select_rtx_section (machine_mode, rtx,
 					    unsigned HOST_WIDE_INT);
diff --git a/gcc/target.def b/gcc/target.def
index 07059a87caf..9bd61b4e018 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -561,6 +561,18 @@ otherwise.",
  section *, (tree decl),
+/* Return the relro section associated with function DECL.  */
+ "Return the relro section associated with\n\
+@samp{DECL_SECTION_NAME (@var{decl})}.\n\
+The default version of this function selects @code{.gnu.linkonce.r.name} if\n\
+the function's section is @code{.gnu.linkonce.t.name}, \n\
+@code{.data.rel.ro.name} if function is in @code{.text.name}, \n\
+and the normal data relro section otherwise.",
+ section *, (tree decl),
+ default_function_relro_section)
 /* Nonnull if the target wants to override the default ".rodata" prefix
    for mergeable data sections.  */
diff --git a/gcc/varasm.c b/gcc/varasm.c

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