[PATCH] arm: Disable unaligned access if MMU is switched off

Andrey Smirnov andrew.smirnov at gmail.com
Wed Sep 23 20:17:25 PDT 2015

Form reading ARM architecture related documentation if appears that
while unaligned memory access is supported by the processor in general
it is not supported if MMU is disabled.

The problem in question can be easilty reproduced by building the code
without this patch, MMU disabled and trying to run 'memtest'
command. Which would in turn call mem_test() which would eventually
call show_progress(). That last function, if build without
-mno-unaligned-access would result in unaligned memory access which
would result in Barebox hanging.

This patch is a very conservative attempt to make sure that any code
that can potentially be executed with MMU disabled is built with
unaligned memory accesses disabled.

Signed-off-by: Andrey Smirnov <andrew.smirnov at gmail.com>
 arch/arm/Makefile      | 14 ++++++++++++++
 scripts/Makefile.build |  2 +-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index 721aa9b..9af4f3b 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -13,6 +13,20 @@ AS		+= -EL
 LD		+= -EL
+# Unaligned access is not supported when MMU is disabled, so if MMU is
+# enabled early on, only PBL, part of which will be executed with MMU
+# diabled, would have to be build with -mno-unaligned-accesses,
+# otherwise set this flag globally
+ifeq ($(CONFIG_MMU_EARLY),y)
+ifneq ($(CONFIG_PBL_IMAGE),y)
+PBL_CFLAGS += -mno-unaligned-access
+CFLAGS += -mno-unaligned-access
 # This selects which instruction set is used.
 # Note that GCC does not numerically define an architecture version
 # macro, but instead defines a whole series of macros which makes
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 56ee072..1624a7a 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -188,7 +188,7 @@ quiet_cmd_pbl_cc_o_c = PBLCC   $@
 cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<
-cmd_pbl_cc_o_c = $(CC) -D__PBL__ $(c_flags) $(PBL_CPPFLAGS) -c -o $@ $<
+cmd_pbl_cc_o_c = $(CC) -D__PBL__ $(c_flags) $(PBL_CFLAGS) $(PBL_CPPFLAGS) -c -o $@ $<
 # When module versioning is enabled the following steps are executed:

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