"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.
So yeah, the patch LGTM to me, thanks.
Richard
