[PATCHv2][ARM] -mpure-code option for ARM

Andre Vieira (lists) Andre.SimoesDiasVieira@arm.com
Mon Jul 11 16:57:00 GMT 2016


On 07/07/16 13:30, mickael guene wrote:
> Hi Andre,
> 
>  Another feedback on your purecode patch.
>  You have to disable casesi pattern since then it will
> generate wrong code with -mpure-code option.
>  Indeed it will generate an 'adr rx, .Lx' (aka
> 'subs rx, PC, #offset') which will not work in our
> case since 'Lx' label is put in an .rodata section.
> So offset value is unknown and can be impossible
> to encode correctly.
> 
> Regards
> Mickael
> 
> On 06/30/2016 04:32 PM, Andre Vieira (lists) wrote:
>> Hello,
>>
>> This patch adds the -mpure-code option for ARM. This option ensures
>> functions are put into sections that contain only code and no data. To
>> ensure this throughout compilation we give these sections the ARM
>> processor-specific ELF section attribute "SHF_ARM_PURECODE". This option
>> is only supported for non-pic code for armv7-m targets.
>>
>> This patch introduces a new target hook 'TARGET_ASM_ELF_FLAGS_NUMERIC'.
>> This target hook enables a target to use the numeric value for elf
>> section attributes rather than their alphabetical representation. If
>> TARGET_ASM_ELF_FLAGS_NUMERIC returns TRUE, the existing
>> 'default_elf_asm_named_section', will print the numeric value of the
>> section attributes for the current section. This target hook has two
>> parameters:
>> unsigned int FLAGS, the input parameter that tells the function the
>> current section's attributes;
>> unsigned int *NUM, used to pass down the numerical representation of the
>> section's attributes.
>>
>> The default implementation for TARGET_ASM_ELF_FLAGS_NUMERIC will return
>> false, so existing behavior is not changed.
>>
>> Bootstrapped and tested for arm-none-linux-gnueabihf. Further tested for
>> arm-none-eabi with a Cortex-M3 target.
>>
>>
>> gcc/ChangeLog:
>> 2016-06-30  Andre Vieira  <andre.simoesdiasvieira@arm.com>
>>             Terry Guo  <terry.guo@arm.com>
>>
>>         * target.def (elf_flags_numeric): New target hook.
>>         * targhooks.h (default_asm_elf_flags_numeric): New.
>>         * varasm.c (default_asm_elf_flags_numeric): New.
>>           (default_elf_asm_named_section): Use new target hook.
>>         * config/arm/arm.opt (mpure-code): New.
>>         * config/arm/arm.h (SECTION_ARM_PURECODE): New.
>>         * config/arm/arm.c (arm_asm_init_sections): Add section
>>           attribute to default text section if -mpure-code.
>>           (arm_option_check_internal): Diagnose use of option with
>>           non supported targets and/or options.
>>           (arm_asm_elf_flags_numeric): New.
>>           (arm_function_section): New.
>>           (arm_elf_section_type_flags): New.
>>         * config/arm/elf.h (JUMP_TABLES_IN_TEXT_SECTION): Disable
>>           for -mpure-code.
>>         * gcc/doc/texi (TARGET_ASM_ELF_FLAGS_NUMERIC): New.
>>         * gcc/doc/texi.in (TARGET_ASM_ELF_FLAGS_NUMERIC): Likewise.
>>
>>
>>
>> gcc/testsuite/ChangeLog:
>> 2016-06-30  Andre Vieira  <andre.simoesdiasvieira@arm.com>
>>             Terry Guo  <terry.guo@arm.com>
>>
>>         * gcc.target/arm/pure-code/ffunction-sections.c: New.
>>         * gcc.target/arm/pure-code/no-literal-pool.c: New.
>>         * gcc.target/arm/pure-code/pure-code.exp: New.
>>
> 
Hi Sandra, Mickael,

Thank you for your comments. I changed the description of -mpure-code in
invoke.texi to better reflect the error message you get wrt supported
targets.

As for the target hook description, I hope the text is clearer now. Let
me know if you think it needs further explanation.

I also fixed the double '%' in the text string for unnamed text sections
and disabled the casesi pattern.

I duplicated the original casesi test
'gcc/testsuite/gcc.c-torture/compile/pr46934.c' for pure-code to make
sure the casesi was disabled and other patterns were selected instead.

Reran regressions for pure-code.exp for Cortex-M3.

Cheers,
Andre


gcc/ChangeLog:
2016-07-11  Andre Vieira  <andre.simoesdiasvieira@arm.com>
            Terry Guo  <terry.guo@arm.com>

        * target.def (elf_flags_numeric): New target hook.
        * hooks.c (hook_uint_uintp_false): New generic hook.
        * varasm.c (default_elf_asm_named_section): Use new target hook.
        * config/arm/arm.opt (mpure-code): New.
        * config/arm/arm.h (SECTION_ARM_PURECODE): New.
        * config/arm/arm.c (arm_asm_init_sections): Add section
        attribute to default text section if -mpure-code.
        (arm_option_check_internal): Diagnose use of option with
        non supported targets and/or options.
        (arm_asm_elf_flags_numeric): New.
        (arm_function_section): New.
        (arm_elf_section_type_flags): New.
        * config/arm/elf.h (JUMP_TABLES_IN_TEXT_SECTION): Disable
        for -mpure-code.
        * config/arm/arm.md (casesi): Disable pattern for
        -mpure-code.
        * gcc/doc/texi (TARGET_ASM_ELF_FLAGS_NUMERIC): New.
        * gcc/doc/texi.in (TARGET_ASM_ELF_FLAGS_NUMERIC): Likewise.



gcc/testsuite/ChangeLog:
2016-07-11  Andre Vieira  <andre.simoesdiasvieira@arm.com>
            Terry Guo  <terry.guo@arm.com>

        * gcc.target/arm/pure-code/ffunction-sections.c: New.
        * gcc.target/arm/pure-code/no-literal-pool.c: New.
        * gcc.target/arm/pure-code/no-casesi.c: New.
        * gcc.target/arm/pure-code/pure-code.exp: New.
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