Segher,
Seems I sent the wrong diff file. Now the attachments should be correct
ones. Sorry for that.
For the reloc, my understanding is the jump table needs to be relocated
if it's a non-relative jump table and PIC flag is set at the same time.
//stmt.c
if (CASE_VECTOR_PC_RELATIVE
|| (flag_pic && targetm.asm_out.generate_pic_addr_diff_vec ()))
emit_jump_table_data (gen_rtx_ADDR_DIFF_VEC (CASE_VECTOR_MODE,
gen_rtx_LABEL_REF (Pmode,
table_label),
gen_rtvec_v (ncases,
labelvec),
const0_rtx, const0_rtx));
else
emit_jump_table_data (gen_rtx_ADDR_VEC (CASE_VECTOR_MODE,
gen_rtvec_v (ncases,
labelvec)));
According to the slice of code in stmt.c, the non-relative jump table
is created with PIC flag set when CASE_VECTOR_PC_RELATIVE is false,
flag_pic is true and targetm.asm_out.generate_pic_addr_diff_vec is
false. So I set the reloc to
reloc = (! CASE_VECTOR_PC_RELATIVE && flag_pic &&
! targetm.asm_out.generate_pic_addr_diff_vec ()) ? 1 : 0;
The funcation_rodata_section is not only for jump tables. It's no relro
in other cases. I am not sure if it's suitable to put selecting relro
section in it. Of course, I can create a separate function for section
selection of jump table and send its output to funcation_rodata_section.
Please advice. Thanks a lot.
On 15/8/2020 上午 7:39, Segher Boessenkool wrote:
Hi!
On Fri, Aug 14, 2020 at 03:20:03PM +0800, HAO CHEN GUI wrote:
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;
(Modern style is no space after "!", and your mailer wrapped the code).
section_reloc = (reloc & targetm.asm_out.reloc_rw_mask ());
(No space after & either).
return targetm.asm_out.function_rodata_section (decl, section_reloc);
So you are saying it should not go into relro if either there is no pic
flag, the targets are pc relative, or pic uses some address diff?
This seems too complicated, and/or not the right abstraction.
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.
@hook TARGET_ASM_FUNCTION_RODATA_SECTION
+@hook TARGET_ASM_FUNCTION_RELRO_SECTION
I would expect people to just use TARGET_ASM_FUNCTION_RODATA_SECTION to
get the .data.rel.ro? With another argument then.
+section *
+select_jump_table_section (tree decl)
+{
+ int relco;
"reloc"?
+ relco = JUMP_TABLES_IN_RELRO;
Just put that on the same line as the declaration?
+ 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);
+}
(trailing spaces btw)
@@ -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
(current_function_decl));
section *section
= select_jump_table_section (current_function_decl));
switch_to_section (section);
(but it would be better if we didn't indent so deeply here).
I think this should be split into a function just selecting the relro
section (either directly, or from the rodata selection function), and
then separately the jumptable section thing.
There is a lot of stuff here that seems confused, and a lot of that
already was there :-(
Segher
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
otherwise.
@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.
@hook TARGET_ASM_FUNCTION_RODATA_SECTION
+@hook TARGET_ASM_FUNCTION_RELRO_SECTION
+
@hook TARGET_ASM_MERGEABLE_RODATA_PREFIX
@hook TARGET_ASM_TM_CLONE_TABLE_SECTION
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
#define JUMP_TABLES_IN_TEXT_SECTION 0
#endif
+#ifndef JUMP_TABLES_IN_RELRO
+#define JUMP_TABLES_IN_RELRO 0
+#endif
+
/* 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;
+
+ relco = JUMP_TABLES_IN_RELRO;
+
+ 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
(current_function_decl));
#ifdef ADDR_VEC_ALIGN
@@ -2571,7 +2592,7 @@ final_scan_insn_1 (rtx_insn *insn, FILE *file, int
optimize_p ATTRIBUTE_UNUSED,
#endif
if (! JUMP_TABLES_IN_TEXT_SECTION)
- switch_to_section (targetm.asm_out.function_rodata_section
+ switch_to_section (select_jump_table_section
(current_function_decl));
else
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),
default_function_rodata_section)
+/* Return the relro section associated with function DECL. */
+DEFHOOK
+(function_relro_section,
+ "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. */
DEFHOOKPOD
diff --git a/gcc/varasm.c b/gcc/varasm.c * 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.
