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From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: linux-efi@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H . Peter Anvin" <hpa@zytor.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	linux-kernel@vger.kernel.org,
	Matt Fleming <matt@codeblueprint.co.uk>
Subject: [PATCH 04/14] efi/libstub: arm64: set -fpie when building the EFI stub
Date: Fri, 18 Aug 2017 20:49:37 +0100	[thread overview]
Message-ID: <20170818194947.19347-5-ard.biesheuvel@linaro.org> (raw)
In-Reply-To: <20170818194947.19347-1-ard.biesheuvel@linaro.org>

Clang may emit absolute symbol references when building in non-PIC mode,
even when using the default 'small' code model, which is already mostly
position independent to begin with, due to its use of adrp/add pairs
that have a relative range of +/- 4 GB. The remedy is to pass the -fpie
flag, which can be done safely now that the code has been updated to avoid
GOT indirections (which may be emitted due to the compiler assuming that
the PIC/PIE code may end up in a shared library that is subject to ELF
symbol preemption)

Passing -fpie when building code that needs to execute at an a priori
unknown offset is arguably an improvement in any case, and given that
the recent visibility changes allow the PIC build to pass with GCC as
well, let's add -fpie for all arm64 builds rather than only for Clang.

Cc: Matt Fleming <matt@codeblueprint.co.uk>
Tested-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 drivers/firmware/efi/libstub/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index 37e24f525162..cf81e6cf5ae8 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -10,7 +10,7 @@ cflags-$(CONFIG_X86)		+= -m$(BITS) -D__KERNEL__ -O2 \
 				   -fPIC -fno-strict-aliasing -mno-red-zone \
 				   -mno-mmx -mno-sse
 
-cflags-$(CONFIG_ARM64)		:= $(subst -pg,,$(KBUILD_CFLAGS))
+cflags-$(CONFIG_ARM64)		:= $(subst -pg,,$(KBUILD_CFLAGS)) -fpie
 cflags-$(CONFIG_ARM)		:= $(subst -pg,,$(KBUILD_CFLAGS)) \
 				   -fno-builtin -fpic -mno-single-pic-base
 
-- 
2.11.0

  parent reply	other threads:[~2017-08-18 19:49 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-18 19:49 [GIT PULL 00/14] EFI changes for v4.14 Ard Biesheuvel
2017-08-18 19:49 ` [PATCH 01/14] efi: arm: Don't mark ACPI reclaim memory as MEMBLOCK_NOMAP Ard Biesheuvel
2017-08-18 19:49 ` [PATCH 02/14] efi/libstub: arm64: use hidden attribute for struct screen_info reference Ard Biesheuvel
2017-08-18 19:49 ` Ard Biesheuvel [this message]
2017-08-18 19:49 ` [PATCH 05/14] efi: arm/arm64: Add missing assignment of efi.config_table Ard Biesheuvel
2017-08-18 19:49 ` [PATCH 07/14] drivers/fbdev: efifb: allow BAR to be moved instead of claiming it Ard Biesheuvel
2017-08-18 19:49 ` [PATCH 10/14] arm: efi: replace open coded constants with symbolic ones Ard Biesheuvel
2017-08-18 19:49 ` [PATCH 12/14] firmware: dcdbas: constify attribute_group structures Ard Biesheuvel
     [not found] ` <20170818194947.19347-1-ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
2017-08-18 19:49   ` [PATCH 03/14] efi/libstub: arm64: force 'hidden' visibility for section markers Ard Biesheuvel
2017-08-18 19:49   ` [PATCH 06/14] efi/reboot: Fall back to original power-off method if EFI_RESET_SHUTDOWN returns Ard Biesheuvel
2017-08-18 19:49   ` [PATCH 08/14] arm: efi: remove forbidden values from the PE/COFF header Ard Biesheuvel
2017-08-18 19:49   ` [PATCH 09/14] arm: efi: remove pointless dummy .reloc section Ard Biesheuvel
2017-08-18 19:49   ` [PATCH 11/14] arm: efi: split zImage code and data into separate PE/COFF sections Ard Biesheuvel
2017-08-18 19:49   ` [PATCH 13/14] firmware: efi: constify attribute_group structures Ard Biesheuvel
2017-08-18 19:49 ` [PATCH 14/14] firmware: efi: esrt: " Ard Biesheuvel
2017-08-21  9:34 ` [GIT PULL 00/14] EFI changes for v4.14 Ingo Molnar

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