[PATCH v2] arm64: errata: Add -mpc-relative-literal-loads to build flags

[PATCH v2] arm64: errata: Add -mpc-relative-literal-loads to build flags

[dann frazier]

GCC6 (and Linaro's 2015.12 snapshot of GCC5) has a new default that uses
adrp/ldr or adrp/add to address literal pools. When CONFIG_ARM64_ERRATUM_843419
is enabled, modules built with this toolchain fail to load:

  [ 2.156817] module libahci: unsupported RELA relocation: 275

Longterm, this will likely be superseded by -mfix-cortex-a53-843419, which
should disable this optimization in the future.

v2: Unconditionally use flag for both kernel and modules, as Ard notes we have
no requirement for supporting literals >1 MB away.

Cc: stable at vger.kernel.org
Fixes: df057cc7b4fa ("arm64: errata: add module build workaround for erratum #843419")
BugLink: http://bugs.launchpad.net/bugs/1533009
Suggested-by: Christophe Lyon <christophe.lyon@linaro.org>
Signed-off-by: dann frazier <dann.frazier@canonical.com>
---
 arch/arm64/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index cd822d8..b6c90e5 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -27,6 +27,7 @@ $(warning LSE atomics not supported by binutils)
 endif
 
 KBUILD_CFLAGS	+= -mgeneral-regs-only $(lseinstr)
+KBUILD_CFLAGS	+= $(call cc-option, -mpc-relative-literal-loads)
 KBUILD_AFLAGS	+= $(lseinstr)
 
 ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
-- 
2.7.0

[PATCH v2] arm64: errata: Add -mpc-relative-literal-loads to build flags

[Ard Biesheuvel]

On 26 January 2016 at 00:52, dann frazier <dann.frazier@canonical.com> wrote:
> GCC6 (and Linaro's 2015.12 snapshot of GCC5) has a new default that uses
> adrp/ldr or adrp/add to address literal pools. When CONFIG_ARM64_ERRATUM_843419
> is enabled, modules built with this toolchain fail to load:
>
>   [ 2.156817] module libahci: unsupported RELA relocation: 275
>
> Longterm, this will likely be superseded by -mfix-cortex-a53-843419, which
> should disable this optimization in the future.
>

Better drop this line, it does not apply to partially linked object
files (aka modules), only to fully linked binaries [afaik]

> v2: Unconditionally use flag for both kernel and modules, as Ard notes we have
> no requirement for supporting literals >1 MB away.
>

Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>


> Cc: stable at vger.kernel.org
> Fixes: df057cc7b4fa ("arm64: errata: add module build workaround for erratum #843419")
> BugLink: http://bugs.launchpad.net/bugs/1533009
> Suggested-by: Christophe Lyon <christophe.lyon@linaro.org>
> Signed-off-by: dann frazier <dann.frazier@canonical.com>
> ---
>  arch/arm64/Makefile | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index cd822d8..b6c90e5 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -27,6 +27,7 @@ $(warning LSE atomics not supported by binutils)
>  endif
>
>  KBUILD_CFLAGS  += -mgeneral-regs-only $(lseinstr)
> +KBUILD_CFLAGS  += $(call cc-option, -mpc-relative-literal-loads)
>  KBUILD_AFLAGS  += $(lseinstr)
>
>  ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
> --
> 2.7.0
>