[PATCH] aarch64: Allow PC-relative relocations against protected STT_FUNC

[Fangrui Song]

On Wed, Jun 1, 2022 at 11:50 PM Fangrui Song <maskray@google.com> wrote:
>
>     __attribute__((visibility("protected"))) void *foo() {
>       return (void *)foo;
>     }
>
> gcc -fpic -shared incorrectly fails with:
>
>     relocation R_AARCH64_ADR_PREL_PG_HI21 against symbol `foo' which may bind externally can not be used when making a shared object; recompile with -fPIC
>
> Call _bfd_elf_symbol_refs_local_p with local_protected==true to suppress
> the error.  The new behavior matches gold and ld.lld.
>
> Note: if some code tries to use direct access relocations to take the
> address of foo (likely due to -fno-pic), the pointer equality will
> break, but the error should be reported on that link.
> ---
>  bfd/elfnn-aarch64.c                           |  2 +-
>  ld/testsuite/ld-aarch64/aarch64-elf.exp       |  1 +
>  ld/testsuite/ld-aarch64/pcrel-protected.s     | 13 +++++++++++++
>  ld/testsuite/ld-aarch64/pcrel_pic_protected.d |  7 +++++++
>  4 files changed, 22 insertions(+), 1 deletion(-)
>  create mode 100644 ld/testsuite/ld-aarch64/pcrel-protected.s
>  create mode 100644 ld/testsuite/ld-aarch64/pcrel_pic_protected.d
>
> diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c
> index cb316a928ef..2c8e3439d43 100644
> --- a/bfd/elfnn-aarch64.c
> +++ b/bfd/elfnn-aarch64.c
> @@ -5878,7 +5878,7 @@ elfNN_aarch64_final_link_relocate (reloc_howto_type *howto,
>        if (bfd_link_pic (info)
>           && (input_section->flags & SEC_ALLOC) != 0
>           && (input_section->flags & SEC_READONLY) != 0
> -         && !SYMBOL_REFERENCES_LOCAL (info, h))
> +         && !_bfd_elf_symbol_refs_local_p (h, info, 1))
>         {
>           int howto_index = bfd_r_type - BFD_RELOC_AARCH64_RELOC_START;
>
> diff --git a/ld/testsuite/ld-aarch64/aarch64-elf.exp b/ld/testsuite/ld-aarch64/aarch64-elf.exp
> index 64476f111e0..565a67aa9aa 100644
> --- a/ld/testsuite/ld-aarch64/aarch64-elf.exp
> +++ b/ld/testsuite/ld-aarch64/aarch64-elf.exp
> @@ -248,6 +248,7 @@ run_dump_test_lp64 "local-addend-r"
>  # test error handling on pcrel relocation for shared libraries.
>  run_dump_test_lp64 "pcrel_pic_undefined"
>  run_dump_test_lp64 "pcrel_pic_defined"
> +run_dump_test_lp64 "pcrel_pic_protected"
>
>  run_dump_test "limit-b"
>  run_dump_test "limit-bl"
> diff --git a/ld/testsuite/ld-aarch64/pcrel-protected.s b/ld/testsuite/ld-aarch64/pcrel-protected.s
> new file mode 100644
> index 00000000000..ce2a92851ad
> --- /dev/null
> +++ b/ld/testsuite/ld-aarch64/pcrel-protected.s
> @@ -0,0 +1,13 @@
> +.protected protected_a
> +.protected protected_b
> +.type protected_b, %object
> +.protected protected_c
> +.type protected_c, %function
> +
> +.text
> +       adrp    x0, protected_a
> +       add     x0, x0, :lo12:protected_a
> +       adrp    x0, protected_b
> +       add     x0, x0, :lo12:protected_b
> +       adrp    x0, protected_c
> +       add     x0, x0, :lo12:protected_c
> diff --git a/ld/testsuite/ld-aarch64/pcrel_pic_protected.d b/ld/testsuite/ld-aarch64/pcrel_pic_protected.d
> new file mode 100644
> index 00000000000..1b6f24cf2fb
> --- /dev/null
> +++ b/ld/testsuite/ld-aarch64/pcrel_pic_protected.d
> @@ -0,0 +1,7 @@
> +#name: PC-Rel relocation against protected
> +#source: pcrel-protected.s
> +#target: [check_shared_lib_support]
> +#ld: -shared -e0 --defsym protected_a=0x1000 --defsym protected_b=0x1010 --defsym protected_c=0x1020
> +#readelf: -r -W
> +#...
> +There are no relocations in this file.
> --
> 2.36.1.255.ge46751e96f-goog
>

:)