Re: Fix even more merging PIC and PIE options

[Martin Liška <mliska at suse dot cz>]

On 08/10/2018 04:33 PM, Jan Hubicka wrote:
> Hi,
> this patch should fix merging of PIC and PIE options so we always resort
> to the least common denominator of the object files compiled (i.e. 
> linking together -fpic and -fPIE will result in -fpie binary).
> Note that we also use information about format of output passed by linker
> plugin so we will disable pic/pie when resulting binary is not relocatable.
> However for shared libraries and pie we want to pick right mode that makes
> sense.
> 
> I wrote simple script that tries all possible options of combining two files.
> Mode picked is specified in the output file.
> 
> To support targets that default to pic/pie well, I had to also hack
> lto_write_options to always stream what mode was used in the given file.
> 
> lto-bootstrapped/regtested x86_64-linux, OK?
> 
> Honza

Thank you Honza for it. Would it be then subject for backporting into GCC-8 branch?

Martin

> 
> 	PR lto/86517
> 	* lto-opts.c (lto_write_options): Always stream PIC/PIE mode.
> 	* lto-wrapper.c (merge_and_complain): Fix merging of PIC/PIE
> Index: lto-opts.c
> ===================================================================
> --- lto-opts.c	(revision 263356)
> +++ lto-opts.c	(working copy)
> @@ -78,6 +78,22 @@ lto_write_options (void)
>        && !global_options.x_flag_openacc)
>      append_to_collect_gcc_options (&temporary_obstack, &first_p,
>  				   "-fno-openacc");
> +  /* Append PIC/PIE mode because its default depends on target and it is
> +     subject of merging in lto-wrapper.  */
> +  if ((!global_options_set.x_flag_pic || global_options.x_flag_pic == 0)
> +      && !global_options_set.x_flag_pie)
> +    {
> +       append_to_collect_gcc_options (&temporary_obstack, &first_p,
> +				      global_options.x_flag_pic == 2
> +				      ? "-fPIC"
> +				      : global_options.x_flag_pic == 1
> +				      ? "-fpic"
> +				      : global_options.x_flag_pie == 2
> +				      ? "-fPIE"
> +				      : global_options.x_flag_pie == 1
> +				      ? "-fpie"
> +				      : "-fno-pie");
> +    }
>  
>    /* Append options from target hook and store them to offload_lto section.  */
>    if (lto_stream_offload_p)
> Index: lto-wrapper.c
> ===================================================================
> --- lto-wrapper.c	(revision 263356)
> +++ lto-wrapper.c	(working copy)
> @@ -408,6 +408,11 @@ merge_and_complain (struct cl_decoded_op
>       It is a common mistake to mix few -fPIC compiled objects into otherwise
>       non-PIC code.  We do not want to build everything with PIC then.
>  
> +     Similarly we merge PIE options, however in addition we keep
> +      -fPIC + -fPIE = -fPIE
> +      -fpic + -fPIE = -fpie
> +      -fPIC/-fpic + -fpie = -fpie
> +
>       It would be good to warn on mismatches, but it is bit hard to do as
>       we do not know what nothing translates to.  */
>      
> @@ -415,11 +420,38 @@ merge_and_complain (struct cl_decoded_op
>      if ((*decoded_options)[j].opt_index == OPT_fPIC
>          || (*decoded_options)[j].opt_index == OPT_fpic)
>        {
> -	if (!pic_option
> -	    || (pic_option->value > 0) != ((*decoded_options)[j].value > 0))
> -	  remove_option (decoded_options, j, decoded_options_count);
> -	else if (pic_option->opt_index == OPT_fPIC
> -		 && (*decoded_options)[j].opt_index == OPT_fpic)
> +	/* -fno-pic in one unit implies -fno-pic everywhere.  */
> +	if ((*decoded_options)[j].value == 0)
> +	  j++;
> +	/* If we have no pic option or merge in -fno-pic, we still may turn
> +	   existing pic/PIC mode into pie/PIE if -fpie/-fPIE is present.  */
> +	else if ((pic_option && pic_option->value == 0)
> +		 || !pic_option)
> +	  {
> +	    if (pie_option)
> +	      {
> +		bool big = (*decoded_options)[j].opt_index == OPT_fPIC
> +			   && pie_option->opt_index == OPT_fPIE;
> +	        (*decoded_options)[j].opt_index = big ? OPT_fPIE : OPT_fpie;
> +		if (pie_option->value)
> +	          (*decoded_options)[j].canonical_option[0] = big ? "-fPIE" : "-fpie";
> +		else
> +	          (*decoded_options)[j].canonical_option[0] = big ? "-fno-pie" : "-fno-pie";
> +		(*decoded_options)[j].value = pie_option->value;
> +	        j++;
> +	      }
> +	    else if (pic_option)
> +	      {
> +	        (*decoded_options)[j] = *pic_option;
> +	        j++;
> +	      }
> +	    /* We do not know if target defaults to pic or not, so just remove
> +	       option if it is missing in one unit but enabled in other.  */
> +	    else
> +	      remove_option (decoded_options, j, decoded_options_count);
> +	  }
> +	else if (pic_option->opt_index == OPT_fpic
> +		 && (*decoded_options)[j].opt_index == OPT_fPIC)
>  	  {
>  	    (*decoded_options)[j] = *pic_option;
>  	    j++;
> @@ -430,11 +462,42 @@ merge_and_complain (struct cl_decoded_op
>     else if ((*decoded_options)[j].opt_index == OPT_fPIE
>              || (*decoded_options)[j].opt_index == OPT_fpie)
>        {
> -	if (!pie_option
> -	    || pie_option->value != (*decoded_options)[j].value)
> -	  remove_option (decoded_options, j, decoded_options_count);
> -	else if (pie_option->opt_index == OPT_fPIE
> -		 && (*decoded_options)[j].opt_index == OPT_fpie)
> +	/* -fno-pie in one unit implies -fno-pie everywhere.  */
> +	if ((*decoded_options)[j].value == 0)
> +	  j++;
> +	/* If we have no pie option or merge in -fno-pie, we still preserve
> +	   PIE/pie if pic/PIC is present.  */
> +	else if ((pie_option && pie_option->value == 0)
> +		 || !pie_option)
> +	  {
> +	    /* If -fPIC/-fpic is given, merge it with -fPIE/-fpie.  */
> +	    if (pic_option)
> +	      {
> +		if (pic_option->opt_index == OPT_fpic
> +		    && (*decoded_options)[j].opt_index == OPT_fPIE)
> +		  {
> +	            (*decoded_options)[j].opt_index = OPT_fpie;
> +	            (*decoded_options)[j].canonical_option[0]
> +			 = pic_option->value ? "-fpie" : "-fno-pie";
> +		  }
> +		else if (!pic_option->value)
> +		  (*decoded_options)[j].canonical_option[0] = "-fno-pie";
> +		(*decoded_options)[j].value = pic_option->value;
> +		j++;
> +	      }
> +	    else if (pie_option)
> +	      {
> +	        (*decoded_options)[j] = *pie_option;
> +		j++;
> +	      }
> +	    /* Because we always append pic/PIE options this code path should
> +	       not happen unless the LTO object was built by old lto1 which
> +	       did not contain that logic yet.  */
> +	    else
> +	      remove_option (decoded_options, j, decoded_options_count);
> +	  }
> +	else if (pie_option->opt_index == OPT_fpie
> +		 && (*decoded_options)[j].opt_index == OPT_fPIE)
>  	  {
>  	    (*decoded_options)[j] = *pie_option;
>  	    j++;
>