PING^5 [PATCH] Use the section flag 'o' for __patchable_function_entries

[H.J. Lu]

On Sat, Nov 7, 2020 at 7:47 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Sat, Oct 31, 2020 at 5:01 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > On Fri, Oct 23, 2020 at 5:41 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> > >
> > > On Fri, Oct 2, 2020 at 6:00 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> > > >
> > > > On Thu, Feb 6, 2020 at 6:57 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> > > > >
> > > > > This commit in GNU binutils 2.35:
> > > > >
> > > > > https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=b7d072167715829eed0622616f6ae0182900de3e
> > > > >
> > > > > added the section flag 'o' to .section directive:
> > > > >
> > > > > .section __patchable_function_entries,"awo",@progbits,foo
> > > > >
> > > > > which specifies the symbol name which the section references.  Assembler
> > > > > creates a unique __patchable_function_entries section with the section,
> > > > > where foo is defined, as its linked-to section.  Linker keeps a section
> > > > > if its linked-to section is kept during garbage collection.
> > > > >
> > > > > This patch checks assembler support for the section flag 'o' and uses
> > > > > it to implement __patchable_function_entries section.  Since Solaris may
> > > > > use GNU assembler with Solairs ld.  Even if GNU assembler supports the
> > > > > section flag 'o', it doesn't mean that Solairs ld supports it.  This
> > > > > feature is disabled for Solairs targets.
> > > > >
> > > > > gcc/
> > > > >
> > > > >         PR middle-end/93195
> > > > >         PR middle-end/93197
> > > > >         * configure.ac (HAVE_GAS_SECTION_LINK_ORDER): New.  Define if
> > > > >         the assembler supports the section flag 'o' for specifying
> > > > >         section with link-order.
> > > > >         * dwarf2out.c (output_comdat_type_unit): Pass 0 as flags2
> > > > >         to targetm.asm_out.named_section.
> > > > >         * config/sol2.c (solaris_elf_asm_comdat_section): Likewise.
> > > > >         * output.h (SECTION2_LINK_ORDER): New.
> > > > >         (switch_to_section): Add an unsigned int argument.
> > > > >         (default_no_named_section): Likewise.
> > > > >         (default_elf_asm_named_section): Likewise.
> > > > >         * target.def (asm_out.named_section): Likewise.
> > > > >         * targhooks.c (default_print_patchable_function_entry): Pass
> > > > >         current_function_decl to get_section and SECTION2_LINK_ORDER
> > > > >         to switch_to_section.
> > > > >         * varasm.c (default_no_named_section): Add an unsigned int
> > > > >         argument.
> > > > >         (default_elf_asm_named_section): Add an unsigned int argument,
> > > > >         flags2.  Use 'o' flag for SECTION2_LINK_ORDER if assembler
> > > > >         supports it.
> > > > >         (switch_to_section): Add an unsigned int argument and pass it
> > > > >         to targetm.asm_out.named_section.
> > > > >         (handle_vtv_comdat_section): Pass 0 to
> > > > >         targetm.asm_out.named_section.
> > > > >         * config.in: Regenerated.
> > > > >         * configure: Likewise.
> > > > >         * doc/tm.texi: Likewise.
> > > > >
> > > > > gcc/testsuite/
> > > > >
> > > > >         PR middle-end/93195
> > > > >         * g++.dg/pr93195a.C: New test.
> > > > >         * g++.dg/pr93195b.C: Likewise.
> > > > >         * lib/target-supports.exp
> > > > >         (check_effective_target_o_flag_in_section): New proc.
> > > >
> > > > PING
> > > >
> > > > https://gcc.gnu.org/pipermail/gcc-patches/2020-February/539963.html
> > >
> > > PING.
> > >
> >
> > PING.
> >
>
> PING.

Here is a simpler patch.  OK for master?

This commit in GNU binutils 2.35:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=b7d072167715
829eed0622616f6ae0182900de3e

added the section flag 'o' to .section directive:

.section __patchable_function_entries,"awo",@progbits,foo

which specifies the symbol name which the section references.  Assembler
creates a unique __patchable_function_entries section with the section,
where foo is defined, as its linked-to section.  Linker keeps a section
if its linked-to section is kept during garbage collection.

This patch checks assembler support for the section flag 'o' and uses
it to implement __patchable_function_entries section.  Since Solaris may
use GNU assembler with Solairs ld.  Even if GNU assembler supports the
section flag 'o', it doesn't mean that Solairs ld supports it.  This
feature is disabled for Solairs targets.

gcc/

PR middle-end/93195
PR middle-end/93197
* configure.ac (HAVE_GAS_SECTION_LINK_ORDER): New.  Define 1 if
the assembler supports the section flag 'o' for specifying
section with link-order.
* output.h (SECTION_LINK_ORDER): New.  Defined to 0x4000000.
(SECTION_MACH_DEP): Changed from 0x4000000 to 0x8000000.
* targhooks.c (default_print_patchable_function_entry): Pass
SECTION_LINK_ORDER to switch_to_section if the section flag 'o'
works.  Pass current_function_decl to switch_to_section.
* varasm.c (default_elf_asm_named_section): Use 'o' flag for
SECTION_LINK_ORDER if assembler supports it.
* config.in: Regenerated.
* configure: Likewise.

gcc/testsuite/

PR middle-end/93195
* g++.dg/pr93195a.C: New test.
* g++.dg/pr93195b.C: Likewise.
* lib/target-supports.exp
(check_effective_target_o_flag_in_section): New proc.

-- 
H.J.
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