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++;
>
