[gcc(refs/users/giulianob/heads/pfe_backport_clean)] Backport varasm: Fix up __patchable_function_entries handling

[Giuliano Belinassi <giulianob@gcc.gnu.org>]

https://gcc.gnu.org/g:bb8b3f4aee3c81ccd4d884846a4d87f543c6b75b

commit bb8b3f4aee3c81ccd4d884846a4d87f543c6b75b
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Dec 16 16:15:35 2020 +0100

    Backport varasm: Fix up __patchable_function_entries handling
    
    The SECTION_LINK_ORDER changes don't seem to work properly.
    
    If I compile:
    static inline __attribute__((__gnu_inline__)) __attribute__((__unused__)) __attribute__((patchable_function_entry(0, 0))) int foo (int x)
    {
      return x + 1;
    }
    
    static inline __attribute__((__gnu_inline__)) __attribute__((__unused__)) __attribute__((patchable_function_entry(0, 0))) int bar (int x)
    {
      return x + 2;
    }
    
    int
    baz (int x)
    {
      return foo (x) + 1;
    }
    
    int
    qux (int x)
    {
      return bar (x) + 2;
    }
    (distilled from aarch64 Linux kernel) with
    -O2 -fpatchable-function-entry=2 on aarch64 compiler configured against
    latest binutils, I get:
    ...
            .section        __patchable_function_entries,"awo",@progbits,baz
    ...
            .section        __patchable_function_entries
    ...
    in the assembly, but when it is assembled, one gets:
      [ 4] __patchable_function_entries PROGBITS        0000000000000000 000060 000008 00 WAL  1   0  8
      [ 5] .rela__patchable_function_entries RELA            0000000000000000 000280 000018 18   I 12   4  8
      [ 6] __patchable_function_entries PROGBITS        0000000000000000 000068 000008 00      0   0  8
      [ 7] .rela__patchable_function_entries RELA            0000000000000000 000298 000018 18   I 12   6  8
    i.e. one writable allocated section with SHF_LINK_ORDER and another
    non-allocated non-writable without link order.  In the kernel case there is
    always one entry in the WAL section and then dozens or more in the
    non-allocated one.
    The kernel then fails to link:
    WARNING: modpost: vmlinux.o (__patchable_function_entries): unexpected non-allocatable section.
    Did you forget to use "ax"/"aw" in a .S file?
    Note that for example <linux/init.h> contains
    section definitions for use in .S files.
    ld: .init.data has both ordered [`__patchable_function_entries' in init/main.o] and unordered [`.init.data' in
    +./drivers/firmware/efi/libstub/vsprintf.stub.o] sections
    ld: final link failed: bad value
    make: *** [Makefile:1175: vmlinux] Error 1
    
    The following patch fixes it by always forcing full section flags for
    SECTION_LINK_ORDER sections.
    
    2020-12-16  Jakub Jelinek  <jakub@redhat.com>
    
            * varasm.c (default_elf_asm_named_section): Always force
            section flags even for sections with SECTION_LINK_ORDER flag.

Diff:
---
 gcc/varasm.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/gcc/varasm.c b/gcc/varasm.c
index 7b0792ddaed..9e0e7c0976f 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -6363,9 +6363,10 @@ default_elf_asm_named_section (const char *name, unsigned int flags,
 
   /* If we have already declared this section, we can use an
      abbreviated form to switch back to it -- unless this section is
-     part of a COMDAT groups, in which case GAS requires the full
-     declaration every time.  */
+     part of a COMDAT groups or with SHF_GNU_RETAIN or with SHF_LINK_ORDER,
+     in which case GAS requires the full declaration every time.  */
   if (!(HAVE_COMDAT_GROUP && (flags & SECTION_LINKONCE))
+      && !(flags & (SECTION_RETAIN | SECTION_LINK_ORDER))
       && (flags & SECTION_DECLARED))
     {
       fprintf (asm_out_file, "\t.section\t%s\n", name);