[PATCH] Add support for putting jump table into relocation read-only section
HAO CHEN GUI
guihaoc@linux.ibm.com
Mon Aug 24 07:53:44 GMT 2020
Hi,
I revised the patch according to the advice. The attachment is the
revised change log and diff file. Thanks a lot.
Now it first judges if it's absolute jump table or not. Then decide if
the relocation is needed.
abs_jump_table = (!CASE_VECTOR_PC_RELATIVE
&&
!targetm.asm_out.generate_pic_addr_diff_vec ()) ? 1 : 0;
reloc = (abs_jump_table && targetm.asm_out.reloc_rw_mask ());
switch_to_section (targetm.asm_out.function_rodata_section
(current_function_decl, reloc));
On 17/8/2020 下午 10:50, Segher Boessenkool wrote:
> Hi!
>
> On Mon, Aug 17, 2020 at 10:28:31AM +0800, HAO CHEN GUI wrote:
>>> 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.
> Yes, I did say the *existing* code seems sub-optimal, too :-)
>
>>> 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.
> .data.rel.ro is just another kind of .rodata, one that *can* be
> relocated. So when we use it, fPIC or not doesn't matter. Also, we can
> just use the existing rodata functions for generating .data.rel.ro, and
> it should simplify all code even.
>
>> -@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
> Should this take the 2-bit int "reloc" field like other functions,
> instead of this bool?
>
>
> Segher
-------------- next part --------------
* final.c (final_scan_insn_1): Judge if a jump table is relative or
absoluted, and if it needs to be relocated.
* 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): Add the second argument
to default_function_rodata_section. It indicates the section should be
read-only or relocated read-only.
(default_no_function_rodata_section): Add the second argument.
(function_mergeable_rodata_prefix): 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..b22a7161052 100644
--- a/gcc/config/mips/mips.c
+++ b/gcc/config/mips/mips.c
@@ -9315,10 +9315,10 @@ 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 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))
{
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..b19609f9c96 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{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..54947818320 100644
--- a/gcc/final.c
+++ b/gcc/final.c
@@ -2491,9 +2491,17 @@ final_scan_insn_1 (rtx_insn *insn, FILE *file, int optimize_p ATTRIBUTE_UNUSED,
if (! JUMP_TABLES_IN_TEXT_SECTION)
{
int log_align;
+ bool reloc;
+ bool abs_jump_table;
+
+ abs_jump_table = (!CASE_VECTOR_PC_RELATIVE
+ && !targetm.asm_out.generate_pic_addr_diff_vec ()) ? 1 : 0;
+
+ reloc = (abs_jump_table && targetm.asm_out.reloc_rw_mask ());
+
switch_to_section (targetm.asm_out.function_rodata_section
- (current_function_decl));
+ (current_function_decl, reloc));
#ifdef ADDR_VEC_ALIGN
log_align = ADDR_VEC_ALIGN (table);
@@ -2569,10 +2577,16 @@ final_scan_insn_1 (rtx_insn *insn, FILE *file, int optimize_p ATTRIBUTE_UNUSED,
#if !(defined(ASM_OUTPUT_ADDR_VEC) || defined(ASM_OUTPUT_ADDR_DIFF_VEC))
int vlen, idx;
#endif
+ bool reloc;
+ bool abs_jump_table;
+
+ abs_jump_table = (!CASE_VECTOR_PC_RELATIVE
+ && !targetm.asm_out.generate_pic_addr_diff_vec ()) ? 1 : 0;
+ reloc = (abs_jump_table && targetm.asm_out.reloc_rw_mask ());
if (! JUMP_TABLES_IN_TEXT_SECTION)
switch_to_section (targetm.asm_out.function_rodata_section
- (current_function_decl));
+ (current_function_decl, reloc));
else
switch_to_section (current_function_section ());
diff --git a/gcc/output.h b/gcc/output.h
index eb253c50329..d64963b0ffa 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 reloc);
+extern section *default_no_function_rodata_section (tree, bool reloc);
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..b2e82fcfedc 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -549,16 +549,17 @@ 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 relocated 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 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..19b47ea7c46 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -726,12 +726,26 @@ 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 relocated read-only data section
+ associated with function DECL. */
section *
-default_function_rodata_section (tree decl)
+default_function_rodata_section (tree decl, bool reloc)
{
- if (decl != NULL_TREE && DECL_SECTION_NAME (decl))
+ const char* sname;
+ unsigned int flags;
+
+ flags = 0;
+
+ if (reloc)
+ {
+ sname = ".data.rel.ro.local";
+ flags = (SECTION_WRITE | SECTION_RELRO);
+ }
+ else
+ sname = ".rodata";
+
+ if (decl && DECL_SECTION_NAME (decl))
{
const char *name = DECL_SECTION_NAME (decl);
@@ -744,12 +758,12 @@ 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 +781,18 @@ 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 (reloc)
+ return get_section (sname, flags, decl);
+ else
+ return readonly_data_section;
}
/* Return the read-only data section associated with function DECL
@@ -783,7 +800,8 @@ 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 reloc ATTRIBUTE_UNUSED)
{
return readonly_data_section;
}
@@ -793,7 +811,8 @@ 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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