On Thu, Nov 24, 2022 at 7:26 PM Kewen.Lin via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: > > Hi Richard, > > on 2022/11/23 00:08, Richard Sandiford wrote: > > "Kewen.Lin" <li...@linux.ibm.com> writes: > >> Hi Richard, > >> > >> Many thanks for your review comments! > >> > >>>>> on 2022/8/24 16:17, Kewen.Lin via Gcc-patches wrote: > >>>>>> Hi, > >>>>>> > >>>>>> As discussed in PR98125, -fpatchable-function-entry with > >>>>>> SECTION_LINK_ORDER support doesn't work well on powerpc64 > >>>>>> ELFv1 because the filled "Symbol" in > >>>>>> > >>>>>> .section name,"flags"o,@type,Symbol > >>>>>> > >>>>>> sits in .opd section instead of in the function_section > >>>>>> like .text or named .text*. > >>>>>> > >>>>>> Since we already generates one label LPFE* which sits in > >>>>>> function_section of current_function_decl, this patch is > >>>>>> to reuse it as the symbol for the linked_to section. It > >>>>>> avoids the above ABI specific issue when using the symbol > >>>>>> concluded from current_function_decl. > >>>>>> > >>>>>> Besides, with this support some previous workarounds for > >>>>>> powerpc64 ELFv1 can be reverted. > >>>>>> > >>>>>> btw, rs6000_print_patchable_function_entry can be dropped > >>>>>> but there is another rs6000 patch which needs this rs6000 > >>>>>> specific hook rs6000_print_patchable_function_entry, not > >>>>>> sure which one gets landed first, so just leave it here. > >>>>>> > >>>>>> Bootstrapped and regtested on below: > >>>>>> > >>>>>> 1) powerpc64-linux-gnu P8 with default binutils 2.27 > >>>>>> and latest binutils 2.39. > >>>>>> 2) powerpc64le-linux-gnu P9 (default binutils 2.30). > >>>>>> 3) powerpc64le-linux-gnu P10 (default binutils 2.30). > >>>>>> 4) x86_64-redhat-linux with default binutils 2.30 > >>>>>> and latest binutils 2.39. > >>>>>> 5) aarch64-linux-gnu with default binutils 2.30 > >>>>>> and latest binutils 2.39. > >>>>>> > >> > >> [snip...] > >> > >>>>>> diff --git a/gcc/varasm.cc b/gcc/varasm.cc > >>>>>> index 4db8506b106..d4de6e164ee 100644 > >>>>>> --- a/gcc/varasm.cc > >>>>>> +++ b/gcc/varasm.cc > >>>>>> @@ -6906,11 +6906,16 @@ default_elf_asm_named_section (const char > >>>>>> *name, unsigned int flags, > >>>>>> fprintf (asm_out_file, ",%d", flags & SECTION_ENTSIZE); > >>>>>> if (flags & SECTION_LINK_ORDER) > >>>>>> { > >>>>>> - tree id = DECL_ASSEMBLER_NAME (decl); > >>>>>> - ultimate_transparent_alias_target (&id); > >>>>>> - const char *name = IDENTIFIER_POINTER (id); > >>>>>> - name = targetm.strip_name_encoding (name); > >>>>>> - fprintf (asm_out_file, ",%s", name); > >>>>>> + /* For now, only section "__patchable_function_entries" > >>>>>> + adopts flag SECTION_LINK_ORDER, internal label LPFE* > >>>>>> + was emitted in default_print_patchable_function_entry, > >>>>>> + just place it here for linked_to section. */ > >>>>>> + gcc_assert (!strcmp (name, "__patchable_function_entries")); > >>> > >>> I like the idea of removing the rs600 workaround in favour of making the > >>> target-independent more robust. But this seems a bit hackish. What > >>> would we do if SECTION_LINK_ORDER was used for something else in future? > >>> > >> > >> Good question! I think it depends on how we can get the symbol for the > >> linked_to section, if adopting the name of the decl will suffer the > >> similar issue which this patch wants to fix, we have to reuse the label > >> LPFE* or some kind of new artificial label in the related section; or > >> we can just go with the name of the given decl, or something related to > >> that decl. Since we can't predict any future uses, I just placed an > >> assertion here to ensure that we would revisit and adjust this part at > >> that time. Does it sound reasonable to you? > > > > Yeah, I guess that's good enough. If the old scheme ends up being > > correct for some future use, we can make the new behaviour conditional > > on __patchable_function_entries. > > Yes, we can check if the given section name is > "__patchable_function_entries". > > > > > So yeah, the patch LGTM to me, thanks. > > Thanks again! I rebased and re-tested it on x86/aarch64/powerpc64{,le}, > just committed in r13-4294-gf120196382ac5a. > > BR, > Kewen
Hi, Kewen, do you think whether your patch fixed https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110729 (__patchable_function_entries has wrong sh_link) ? If yes, it may be useful to include some assembly tests... Right now rg '\.section.*__patchable' gcc/testsuite/ returns nothing. -- 宋方睿