[PATCH] Add support for putting jump table into relocation read-only section
HAO CHEN GUI
guihaoc@linux.ibm.com
Mon Aug 17 02:28:31 GMT 2020
Segher,
Please ignore the attachments in my last email. My editor cached the old
things. Now they should be correct. Sorry for that.
On 17/8/2020 上午 10:20, HAO CHEN GUI wrote:
> 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
-------------- 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/config/mips/mips.c b/gcc/config/mips/mips.c
index 513fc5fe295..afb0e1a9f2f 100644
--- a/gcc/config/mips/mips.c
+++ b/gcc/config/mips/mips.c
@@ -9315,10 +9315,11 @@ mips_select_rtx_section (machine_mode mode, rtx x,
default_function_rodata_section. */
static section *
-mips_function_rodata_section (tree decl)
+mips_function_rodata_section (tree decl,
+ bool section_reloc ATTRIBUTE_UNUSED)
{
if (!TARGET_ABICALLS || TARGET_ABSOLUTE_ABICALLS || TARGET_GPWORD)
- return default_function_rodata_section (decl);
+ return default_function_rodata_section (decl, false);
if (decl && DECL_SECTION_NAME (decl))
{
diff --git a/gcc/config/s390/s390.c b/gcc/config/s390/s390.c
index 758315c0c72..eb619d39ad7 100644
--- a/gcc/config/s390/s390.c
+++ b/gcc/config/s390/s390.c
@@ -11639,7 +11639,7 @@ s390_output_split_stack_data (rtx parm_block, rtx call_done,
rtx ops[] = { parm_block, call_done };
switch_to_section (targetm.asm_out.function_rodata_section
- (current_function_decl));
+ (current_function_decl, false));
if (TARGET_64BIT)
output_asm_insn (".align\t8", NULL);
diff --git a/gcc/config/s390/s390.md b/gcc/config/s390/s390.md
index cd1c0634b71..6ca03ed9002 100644
--- a/gcc/config/s390/s390.md
+++ b/gcc/config/s390/s390.md
@@ -11218,7 +11218,7 @@
""
{
switch_to_section (targetm.asm_out.function_rodata_section
- (current_function_decl));
+ (current_function_decl, false));
return "";
}
[(set_attr "length" "0")])
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 6e7d9dc54a9..fd65cc4dbe7 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -7703,13 +7703,13 @@ example, the function @code{foo} would be placed in @code{.text.foo}.
Whatever the actual target object format, this is often good enough.
@end deftypefn
-@deftypefn {Target Hook} {section *} TARGET_ASM_FUNCTION_RODATA_SECTION (tree @var{decl})
-Return the readonly data section associated with
+@deftypefn {Target Hook} {section *} TARGET_ASM_FUNCTION_RODATA_SECTION (tree @var{decl}, bool @var{section_reloc})
+Return the readonly or reloc readonly data 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{.rodata.name}
-if function is in @code{.text.name}, and the normal readonly-data section
-otherwise.
+or @code{.data.rel.ro.name} if function is in @code{.text.name}, and
+the normal readonly-data or reloc readonly data section otherwise.
@end deftypefn
@deftypevr {Target Hook} {const char *} TARGET_ASM_MERGEABLE_RODATA_PREFIX
diff --git a/gcc/final.c b/gcc/final.c
index a3601964a8d..380829db4f7 100644
--- a/gcc/final.c
+++ b/gcc/final.c
@@ -2154,6 +2154,23 @@ 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 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 final scan for one insn, INSN.
Args are same as in `final', except that INSN
is the insn being scanned.
@@ -2492,7 +2509,7 @@ 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 +2588,7 @@ 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..661ce9074ae 100644
--- a/gcc/output.h
+++ b/gcc/output.h
@@ -571,8 +571,8 @@ extern void default_ctor_section_asm_out_constructor (rtx, int);
extern section *default_select_section (tree, int, unsigned HOST_WIDE_INT);
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_rodata_section (tree, bool);
+extern section *default_no_function_rodata_section (tree, bool);
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..fb34507dd89 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -549,16 +549,16 @@ Whatever the actual target object format, this is often good enough.",
void, (tree decl, int reloc),
default_unique_section)
-/* Return the readonly data section associated with function DECL. */
+/* Return the readonly or reloc readonly data section associated with function DECL. */
DEFHOOK
(function_rodata_section,
- "Return the readonly data section associated with\n\
+ "Return the readonly or reloc readonly data 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}, @code{.rodata.name}\n\
-if function is in @code{.text.name}, and the normal readonly-data section\n\
-otherwise.",
- section *, (tree decl),
+or @code{.data.rel.ro.name} if function is in @code{.text.name}, and \n\
+the normal readonly-data or reloc readonly data section otherwise.",
+ section *, (tree decl, bool section_reloc),
default_function_rodata_section)
/* Nonnull if the target wants to override the default ".rodata" prefix
diff --git a/gcc/varasm.c b/gcc/varasm.c
index 4070f9c17e8..bf5a8fbb0ea 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -726,12 +726,25 @@ switch_to_other_text_partition (void)
switch_to_section (current_function_section ());
}
-/* Return the read-only data section associated with function DECL. */
+/* Return the read-only or relocation read-only data section associated with function DECL. */
section *
-default_function_rodata_section (tree decl)
+default_function_rodata_section (tree decl, bool section_reloc)
{
- if (decl != NULL_TREE && DECL_SECTION_NAME (decl))
+ const char* sname;
+ unsigned int flags;
+
+ flags = 0;
+
+ if (section_reloc)
+ {
+ sname = ".data.rel.ro";
+ flags = (SECTION_WRITE | SECTION_RELRO);
+ }
+ else
+ sname = ".rodata";
+
+ if (decl && DECL_SECTION_NAME (decl))
{
const char *name = DECL_SECTION_NAME (decl);
@@ -744,12 +757,12 @@ default_function_rodata_section (tree decl)
dot = strchr (name + 1, '.');
if (!dot)
dot = name;
- len = strlen (dot) + 8;
+ len = strlen (dot) + strlen (sname) + 1;
rname = (char *) alloca (len);
- strcpy (rname, ".rodata");
+ strcpy (rname, sname);
strcat (rname, dot);
- return get_section (rname, SECTION_LINKONCE, decl);
+ return get_section (rname, (SECTION_LINKONCE | flags), decl);
}
/* For .gnu.linkonce.t.foo we want to use .gnu.linkonce.r.foo. */
else if (DECL_COMDAT_GROUP (decl)
@@ -767,15 +780,18 @@ default_function_rodata_section (tree decl)
&& strncmp (name, ".text.", 6) == 0)
{
size_t len = strlen (name) + 1;
- char *rname = (char *) alloca (len + 2);
+ char *rname = (char *) alloca (len + strlen(sname) - 5);
- memcpy (rname, ".rodata", 7);
- memcpy (rname + 7, name + 5, len - 5);
- return get_section (rname, 0, decl);
+ memcpy (rname, sname, strlen(sname));
+ memcpy (rname + strlen(sname), name + 5, len - 5);
+ return get_section (rname, flags, decl);
}
}
- return readonly_data_section;
+ if (section_reloc)
+ return get_section (sname, flags, decl);
+ else
+ return readonly_data_section;
}
/* Return the read-only data section associated with function DECL
@@ -783,7 +799,8 @@ default_function_rodata_section (tree decl)
readonly data section. */
section *
-default_no_function_rodata_section (tree decl ATTRIBUTE_UNUSED)
+default_no_function_rodata_section (tree decl ATTRIBUTE_UNUSED,
+ bool section_reloc ATTRIBUTE_UNUSED)
{
return readonly_data_section;
}
@@ -793,7 +810,8 @@ default_no_function_rodata_section (tree decl ATTRIBUTE_UNUSED)
static const char *
function_mergeable_rodata_prefix (void)
{
- section *s = targetm.asm_out.function_rodata_section (current_function_decl);
+ section *s = targetm.asm_out.function_rodata_section (current_function_decl,
+ false);
if (SECTION_STYLE (s) == SECTION_NAMED)
return s->named.name;
else
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