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common/cmd_boot: keep ARM v7M in thumb mode during do_go_exec()

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On ARM v7M, the processor will return to ARM mode when executing
a blx instruction with bit 0 of the address == 0. Always set it
to 1 to stay in thumb mode.

Signed-off-by: Matt Porter <mporter@konsulko.com>
This commit is contained in:
Matt Porter 2015-05-05 15:00:23 -04:00 committed by Tom Rini
parent c777efe3a1
commit f99993c108
2 changed files with 45 additions and 0 deletions
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1
arch/arm/lib/Makefile
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@ -26,6 +26,7 @@ ifndef CONFIG_SYS_GENERIC_BOARD
obj-y += board.o
endif
obj-$(CONFIG_CPU_V7M) += cmd_boot.o
obj-$(CONFIG_OF_LIBFDT) += bootm-fdt.o
obj-$(CONFIG_CMD_BOOTM) += bootm.o
obj-$(CONFIG_SYS_L2_PL310) += cache-pl310.o

44
arch/arm/lib/cmd_boot.c Normal file
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@ -0,0 +1,44 @@
/*
* (C) Copyright 2008-2011
* Graeme Russ, <graeme.russ@gmail.com>
*
* (C) Copyright 2002
* Daniel Engström, Omicron Ceti AB, <daniel@omicron.se>
*
* (C) Copyright 2002
* Wolfgang Denk, DENX Software Engineering, <wd@denx.de>
*
* (C) Copyright 2002
* Sysgo Real-Time Solutions, GmbH <www.elinos.com>
* Marius Groeger <mgroeger@sysgo.de>
*
* Copyright 2015 ATS Advanced Telematics Systems GmbH
* Copyright 2015 Konsulko Group, Matt Porter <mporter@konsulko.com>
*
* SPDX-License-Identifier: GPL-2.0+
*/
#include <common.h>
#include <command.h>
DECLARE_GLOBAL_DATA_PTR;
/*
* ARMv7M does not support ARM instruction mode. However, the
* interworking BLX and BX instructions do encode the ARM/Thumb
* field in bit 0. This means that when executing any Branch
* and eXchange instruction we must set bit 0 to one to guarantee
* that we keep the processor in Thumb instruction mode. From The
* ARMv7-M Instruction Set A4.1.1:
* "ARMv7-M only supports the Thumb instruction execution state,
* therefore the value of address bit [0] must be 1 in interworking
* instructions, otherwise a fault occurs."
*/
unsigned long do_go_exec(ulong (*entry)(int, char * const []),
int argc, char * const argv[])
{
ulong addr = (ulong)entry | 1;
entry = (void *)addr;
return entry(argc, argv);
}