From: Fangrui Song <maskray@google.com>
To: binutils@sourceware.org, Szabolcs Nagy <szabolcs.nagy@arm.com>,
Nick Clifton <nickc@redhat.com>
Subject: Re: [PATCH] aarch64: Define elf_backend_extern_protected_data to 0 [PR 18705]
Date: Wed, 22 Jun 2022 10:58:44 -0700 [thread overview]
Message-ID: <CAFP8O3J7uSEH1W+nzgfpM7PxcqL+cGy6J-JD_FJs7fOpOxnaHA@mail.gmail.com> (raw)
In-Reply-To: <20220602042059.2898835-1-maskray@google.com>
On Wed, Jun 1, 2022 at 9:21 PM Fangrui Song <maskray@google.com> wrote:
>
> If an executable has copy relocations for extern protected data, that
> can only work if the library containing the definition is built with
> assumptions (a) the compiler emits GOT-generating relocations (b) the
> linker produces R_*_GLOB_DAT instead of R_*_RELATIVE. Otherwise the
> library uses its own definition directly and the executable accesses a
> stale copy.
>
> Commit 32f573bcb3aaa1c9defcad79dbb5851fcc02ae2d changed ld to produce
> R_AARCH64_GLOB_DAT but that defeated the purpose of protected visibility
> as an optimization. Restore the previous behavior (which matches
> ld.lld) by defining elf_backend_extern_protected_data to 0.
> ---
> bfd/elfnn-aarch64.c | 2 +-
> ld/testsuite/ld-aarch64/protected-data.d | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c
> index 4926bab9cf2..cb316a928ef 100644
> --- a/bfd/elfnn-aarch64.c
> +++ b/bfd/elfnn-aarch64.c
> @@ -10090,7 +10090,7 @@ const struct elf_size_info elfNN_aarch64_size_info =
> #define elf_backend_dtrel_excludes_plt 1
> #define elf_backend_got_header_size (GOT_ENTRY_SIZE * 3)
> #define elf_backend_default_execstack 0
> -#define elf_backend_extern_protected_data 1
> +#define elf_backend_extern_protected_data 0
> #define elf_backend_hash_symbol elf_aarch64_hash_symbol
>
> #undef elf_backend_obj_attrs_section
> diff --git a/ld/testsuite/ld-aarch64/protected-data.d b/ld/testsuite/ld-aarch64/protected-data.d
> index 5dabf04748c..ee9b4cfc6b5 100644
> --- a/ld/testsuite/ld-aarch64/protected-data.d
> +++ b/ld/testsuite/ld-aarch64/protected-data.d
> @@ -2,4 +2,4 @@
> #ld: -shared
> #readelf: -r -W
> #...
> -.* R_AARCH64_GLOB_DAT .* var.*
> +.* R_AARCH64_RELATIVE .*
> --
> 2.36.1.255.ge46751e96f-goog
>
:)
next prev parent reply other threads:[~2022-06-22 17:58 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-02 4:20 Fangrui Song
2022-06-22 17:58 ` Fangrui Song [this message]
2022-06-23 7:58 ` Szabolcs Nagy
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