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 --- v3: - Implement using an override of the weak do_go_exec() when building for ARMv7-M.
arch/arm/lib/Makefile | 1 + arch/arm/lib/cmd_boot.c | 44 ++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 45 insertions(+) create mode 100644 arch/arm/lib/cmd_boot.c
diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile index 8288d2f..4c95a77 100644 --- a/arch/arm/lib/Makefile +++ b/arch/arm/lib/Makefile @@ -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 diff --git a/arch/arm/lib/cmd_boot.c b/arch/arm/lib/cmd_boot.c new file mode 100644 index 0000000..37bb6a5 --- /dev/null +++ b/arch/arm/lib/cmd_boot.c @@ -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); +}