Commit 1515b186 authored May 19, 2017 by Russell King

ARM: make configuration of userspace Thumb support an expert option



David Mosberger reports random segfaults and other problems when running
his buildroot userspace.  It turns out that his kernel did not have
support for Thumb userspace, nor did his application, but glibc made use
of Thumb instructions in glibc.

The kernel Thumb support option already recommends being enabled, and
is also so biased, but clearly this is not enough of a recommendation.

So, hide this behind CONFIG_EXPERT as well, and include a note to
indicate the potential issues if it's turned off and userspace Thumb
mode is made use of.

Reported-by: David Mosberger <davidm@egauge.net>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

parent 801f19b9

arch/arm/mm/Kconfig

+5 −1

Original line number	Diff line number	Diff line
		@@ -679,7 +679,7 @@ config ARCH_DMA_ADDR_T_64BIT
		bool

		config ARM_THUMB
		bool "Support Thumb user binaries" if !CPU_THUMBONLY
		bool "Support Thumb user binaries" if !CPU_THUMBONLY && EXPERT
		depends on CPU_THUMB_CAPABLE
		default y
		help
		@@ -690,6 +690,10 @@ config ARM_THUMB
		instruction set resulting in smaller binaries at the expense of
		slightly less efficient code.

		If this option is disabled, and you run userspace that switches to
		Thumb mode, signal handling will not work correctly, resulting in
		segmentation faults or illegal instruction aborts.

		If you don't know what this all is, saying Y is a safe choice.

		config ARM_THUMBEE