[PATCH] ARM: drop Thumb-2 workaround for ancient binutils

From: Ard Biesheuvel <ardb@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: Dave Martin <Dave.Martin@arm.com>,
	linus.walleij@linaro.org, linux@armlinux.org.uk, arnd@arndb.de,
	Ard Biesheuvel <ardb@kernel.org>
Subject: [PATCH] ARM: drop Thumb-2 workaround for ancient binutils
Date: Thu,  7 May 2020 11:33:49 +0200	[thread overview]
Message-ID: <20200507093349.25313-1-ardb@kernel.org> (raw)

The CONFIG_THUMB2_AVOID_R_ARM_THM_JUMP11 workaround addresses an issue
which was fixed before the oldest supported binutils (2.23 at this time)
were released. So we can remove it now.

Cc: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm/Kconfig  | 31 -------------------------------
 arch/arm/Makefile |  4 ----
 2 files changed, 35 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 165987aa5bcd..9a4d4c14fbde 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1425,37 +1425,6 @@ config THUMB2_KERNEL
 
 	  If unsure, say N.
 
-config THUMB2_AVOID_R_ARM_THM_JUMP11
-	bool "Work around buggy Thumb-2 short branch relocations in gas"
-	depends on THUMB2_KERNEL && MODULES
-	default y
-	help
-	  Various binutils versions can resolve Thumb-2 branches to
-	  locally-defined, preemptible global symbols as short-range "b.n"
-	  branch instructions.
-
-	  This is a problem, because there's no guarantee the final
-	  destination of the symbol, or any candidate locations for a
-	  trampoline, are within range of the branch.  For this reason, the
-	  kernel does not support fixing up the R_ARM_THM_JUMP11 (102)
-	  relocation in modules at all, and it makes little sense to add
-	  support.
-
-	  The symptom is that the kernel fails with an "unsupported
-	  relocation" error when loading some modules.
-
-	  Until fixed tools are available, passing
-	  -fno-optimize-sibling-calls to gcc should prevent gcc generating
-	  code which hits this problem, at the cost of a bit of extra runtime
-	  stack usage in some cases.
-
-	  The problem is described in more detail at:
-	      https://bugs.launchpad.net/binutils-linaro/+bug/725126
-
-	  Only Thumb-2 kernels are affected.
-
-	  Unless you are sure your tools don't have this problem, say Y.
-
 config ARM_PATCH_IDIV
 	bool "Runtime patch udiv/sdiv instructions into __aeabi_{u}idiv()"
 	depends on CPU_32v7 && !XIP_KERNEL
diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index 7d5cd0f85461..ba65205ab609 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -125,10 +125,6 @@ AFLAGS_NOWARN	:=$(call as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W)
 ifeq ($(CONFIG_THUMB2_KERNEL),y)
 CFLAGS_ISA	:=-mthumb -Wa,-mimplicit-it=always $(AFLAGS_NOWARN)
 AFLAGS_ISA	:=$(CFLAGS_ISA) -Wa$(comma)-mthumb
-# Work around buggy relocation from gas if requested:
-ifeq ($(CONFIG_THUMB2_AVOID_R_ARM_THM_JUMP11),y)
-KBUILD_CFLAGS_MODULE	+=-fno-optimize-sibling-calls
-endif
 else
 CFLAGS_ISA	:=$(call cc-option,-marm,) $(AFLAGS_NOWARN)
 AFLAGS_ISA	:=$(CFLAGS_ISA)
-- 
2.17.1


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