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