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Re: [patch] [arm] New option for PIC offset unfixed


On 13/11/13 06:18, Joey Ye wrote:
>> -----Original Message-----
>> From: Richard Earnshaw
>> Sent: Tuesday, November 12, 2013 18:49
>> To: Joey Ye
>> Cc: gcc-patches@gcc.gnu.org
>> Subject: Re: [patch] [arm] New option for PIC offset unfixed
>>
>> The name of the option and the documentation highlights that the
>> option's concept is confusing.
>>
>> I think what you really need to do is to reverse the sense of the option
>> name and have
>>
>> -mpic-data-is-text-relative
>>
>> with the inverse (-mno-pic-data-is-text-relative) being the active value
>> that triggers for vxworks.  That is, PIC data being text-relative is the
>> default for all targets except vxworks.
>>
>> R.
>>
>> Oh, and at run time, we should be talking about segments, not sections!
> Richard, Thanks for quick response.
> 
> Updated patch renamed the option, variables and macro. Also use segments in
> document. OK?
> 
> 2013-11-13  Joey Ye  <joey.ye@arm.com>
> 
> 	* config/arm/arm.c (arm_option_override):  Error if
> 	-mpic-data-is-text-relative without -fpic, and set for
> 	VxWorks RTP.
> 	(legitimize_pic_address): Use arm_pic_data_is_text_relative
> 	(arm_assemble_integer): Likewise.
> 	* config/arm/arm.h
> 	(TARGET_DEFAULT_PIC_DATA_IS_TEXT_RELATIVE): New macro.
> 	* config/arm/arm.opt (mpic-data-is-text-relative): New option.
> 	* doc/invoke.texi (-mpic-data-is-text-relative): Doc for new option.
> 
> 
> pic_data_text_rel-1113.patch.txt
> 
> 
> diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
> index 7757e86..fdd5684 100644
> --- a/gcc/config/arm/arm.c
> +++ b/gcc/config/arm/arm.c
> @@ -2504,6 +2504,13 @@ arm_option_override (void)
>  	arm_pic_register = pic_register;
>      }
>  
> +  if (TARGET_VXWORKS_RTP)
> +    arm_pic_data_is_text_relative = 0;

Why is this needed?  Surely, even a VxWorks user should have the right
to force the compiler to behave differently.  You've set things up
through the default, now just accept what the user has asked for.


> +
> +  if (arm_pic_data_is_text_relative != TARGET_DEFAULT_PIC_DATA_IS_TEXT_RELATIVE
> +      && !flag_pic)
> +    error ("-mpic-data-is-text-relative must be used with -fpic");

I'm not sure about this either.  The option should just be ignored when
not PIC.

> +
>    /* Enable -mfix-cortex-m3-ldrd by default for Cortex-M3 cores.  */
>    if (fix_cm3_ldrd == 2)
>      {
> @@ -6020,7 +6027,7 @@ legitimize_pic_address (rtx orig, enum machine_mode mode, rtx reg)
>  	   || (GET_CODE (orig) == SYMBOL_REF &&
>  	       SYMBOL_REF_LOCAL_P (orig)))
>  	  && NEED_GOT_RELOC
> -	  && !TARGET_VXWORKS_RTP)
> +	  && arm_pic_data_is_text_relative)
>  	insn = arm_pic_static_addr (orig, reg);
>        else
>  	{
> @@ -21498,7 +21505,7 @@ arm_assemble_integer (rtx x, unsigned int size, int aligned_p)
>  	{
>  	  /* See legitimize_pic_address for an explanation of the
>  	     TARGET_VXWORKS_RTP check.  */
> -	  if (TARGET_VXWORKS_RTP
> +	  if (!arm_pic_data_is_text_relative
>  	      || (GET_CODE (x) == SYMBOL_REF && !SYMBOL_REF_LOCAL_P (x)))
>  	    fputs ("(GOT)", asm_out_file);
>  	  else
> diff --git a/gcc/config/arm/arm.h b/gcc/config/arm/arm.h
> index 1781b75..dbd841e 100644
> --- a/gcc/config/arm/arm.h
> +++ b/gcc/config/arm/arm.h
> @@ -568,6 +568,10 @@ extern int prefer_neon_for_64bits;
>  #define NEED_PLT_RELOC	0
>  #endif
>  
> +#ifndef TARGET_DEFAULT_PIC_DATA_IS_TEXT_RELATIVE
> +#define TARGET_DEFAULT_PIC_DATA_IS_TEXT_RELATIVE 1
> +#endif
> +
>  /* Nonzero if we need to refer to the GOT with a PC-relative
>     offset.  In other words, generate
>  
> diff --git a/gcc/config/arm/arm.opt b/gcc/config/arm/arm.opt
> index 9b74038..fa0839a 100644
> --- a/gcc/config/arm/arm.opt
> +++ b/gcc/config/arm/arm.opt
> @@ -158,6 +158,10 @@ mlong-calls
>  Target Report Mask(LONG_CALLS)
>  Generate call insns as indirect calls, if necessary
>  
> +mpic-data-is-text-relative
> +Target Report Var(arm_pic_data_is_text_relative) Init(TARGET_DEFAULT_PIC_DATA_IS_TEXT_RELATIVE)
> +Assume data segments are relative to text segment.
                           ^
Assume data segment will be loaded at a fixed relative offset to the
text segment.

> +
>  mpic-register=
>  Target RejectNegative Joined Var(arm_pic_register_string)
>  Specify the register to be used for PIC addressing
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 863e518..298fcc3 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -12120,6 +12120,12 @@ before execution begins.
>  Specify the register to be used for PIC addressing.  The default is R10
>  unless stack-checking is enabled, when R9 is used.
>  
> +@item -mpic-data-is-text-relative
> +@opindex mpic-data-is-text-relative
> +Assume that each data segments are relative to text segment at load time.

> +Therefore, prevent PC relative and GOTOFF style relocations to reference
> +data.  

I think the sense of this sentence is now backwards.  I'd also try to
avoid GOTOFF in the user part of the manual.

> This is on by default for targets other than VxWorks RTP.
> +
>  @item -mpoke-function-name
>  @opindex mpoke-function-name
>  Write the name of each function into the text section, directly
> 

R.


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