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>

diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index c6c4c9c8824b0f4b3c354538306d1c195ad7e90d..4f68659abe6c5ac9900022d2db21e7fb9809c126 100644 (file)
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -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