https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115324
--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-13 branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:50b5019fde97c20a377e004c9d73df62e4898773 commit r13-8834-g50b5019fde97c20a377e004c9d73df62e4898773 Author: Jakub Jelinek <ja...@redhat.com> Date: Mon Jun 3 23:11:06 2024 +0200 rs6000: Fix up PCH in --enable-host-pie builds [PR115324] PCH doesn't work properly in --enable-host-pie configurations on powerpc*-linux*. The problem is that the rs6000_builtin_info and rs6000_instance_info arrays mix pointers to .rodata/.data (bifname and attr_string point to string literals in .rodata section, and the next member is either NULL or &rs6000_instance_info[XXX]) and GC member (tree fntype). Now, for normal GC this works just fine, we emit { &rs6000_instance_info[0].fntype, 1 * (RS6000_INST_MAX), sizeof (rs6000_instance_info[0]), >_ggc_mx_tree_node, >_pch_nx_tree_node }, { &rs6000_builtin_info[0].fntype, 1 * (RS6000_BIF_MAX), sizeof (rs6000_builtin_info[0]), >_ggc_mx_tree_node, >_pch_nx_tree_node }, GC roots which are strided and thus cover only the fntype members of all the elements of the two arrays. For PCH though it actually results in saving those huge arrays (one is 130832 bytes, another 81568 bytes) into the .gch files and loading them back in full. While the bifname and attr_string and next pointers are marked as GTY((skip)), they are actually saved to point to the .rodata and .data sections of the process which writes the PCH, but because cc1/cc1plus etc. are position independent executables with --enable-host-pie, when it is loaded from the PCH file, it can point in a completely different addresses where nothing is mapped at all or some random different thing appears at. While gengtype supports the callback option, that one is meant for relocatable function pointers and doesn't work in the case of GTY arrays inside of .data section anyway. So, either we'd need to add some further GTY extensions, or the following patch instead reworks it such that the fntype members which were the only reason for PCH in those arrays are moved to separate arrays. Size-wise in .data sections it is (in bytes): vanilla patched rs6000_builtin_info 130832 110704 rs6000_instance_info 81568 40784 rs6000_overload_info 7392 7392 rs6000_builtin_info_fntype 0 10064 rs6000_instance_info_fntype 0 20392 sum 219792 189336 where previously we saved/restored for PCH those 130832+81568 bytes, now we save/restore just 10064+20392 bytes, so this change is beneficial for the data section size. Unfortunately, it grows the size of the rs6000_init_generated_builtins function, vanilla had 218328 bytes, patched has 228668. When I applied void rs6000_init_generated_builtins () { + bifdata *rs6000_builtin_info_p; + tree *rs6000_builtin_info_fntype_p; + ovlddata *rs6000_instance_info_p; + tree *rs6000_instance_info_fntype_p; + ovldrecord *rs6000_overload_info_p; + __asm ("" : "=r" (rs6000_builtin_info_p) : "0" (rs6000_builtin_info)); + __asm ("" : "=r" (rs6000_builtin_info_fntype_p) : "0" (rs6000_builtin_info_fntype)); + __asm ("" : "=r" (rs6000_instance_info_p) : "0" (rs6000_instance_info)); + __asm ("" : "=r" (rs6000_instance_info_fntype_p) : "0" (rs6000_instance_info_fntype)); + __asm ("" : "=r" (rs6000_overload_info_p) : "0" (rs6000_overload_info)); + #define rs6000_builtin_info rs6000_builtin_info_p + #define rs6000_builtin_info_fntype rs6000_builtin_info_fntype_p + #define rs6000_instance_info rs6000_instance_info_p + #define rs6000_instance_info_fntype rs6000_instance_info_fntype_p + #define rs6000_overload_info rs6000_overload_info_p + hack by hand, the size of the function is 209700 though, so if really wanted, we could add __attribute__((__noipa__)) to the function when building with recent enough GCC and pass pointers to the first elements of the 5 arrays to the function as arguments. If you want such a change, could that be done incrementally? 2024-06-03 Jakub Jelinek <ja...@redhat.com> PR target/115324 * config/rs6000/rs6000-gen-builtins.cc (write_decls): Remove GTY markup from struct bifdata and struct ovlddata and remove their fntype members. Change next member in struct ovlddata and first_instance member of struct ovldrecord to have int type rather than struct ovlddata *. Remove GTY markup from rs6000_builtin_info and rs6000_instance_info arrays, declare new rs6000_builtin_info_fntype and rs6000_instance_info_fntype arrays, which have GTY markup. (write_bif_static_init): Adjust for the above changes. (write_ovld_static_init): Likewise. (write_init_bif_table): Likewise. (write_init_ovld_table): Likewise. * config/rs6000/rs6000-builtin.cc (rs6000_init_builtins): Likewise. * config/rs6000/rs6000-c.cc (find_instance): Likewise. Make static. (altivec_resolve_overloaded_builtin): Adjust for the above changes. (cherry picked from commit 4cf2de9b5268224816a3d53fdd2c3d799ebfd9c8)
