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?
BR,
Kewen
