> On 07.05.2018, at 10:25, Chris Packham <judge.pack...@gmail.com> wrote: > > Hi Mans, Stefano, > > On Fri, Apr 27, 2018 at 9:00 PM Stefano Babic <sba...@denx.de> wrote: > >> On 21/04/2018 17:11, Mans Rullgard wrote: >>> The code attempts to preserve the value of LR by storing it in R12/IP >>> across the lowevel_init() call. However, this register is not saved >>> by the callee. Use a register that guaranteed to be preserved instead. >>> >>> Signed-off-by: Mans Rullgard <m...@mansr.com> >>> --- >>> arch/arm/cpu/arm926ejs/start.S | 4 ++-- >>> 1 file changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/arch/arm/cpu/arm926ejs/start.S > b/arch/arm/cpu/arm926ejs/start.S >>> index 959d1ed86d8a..a6f0bdb70345 100644 >>> --- a/arch/arm/cpu/arm926ejs/start.S >>> +++ b/arch/arm/cpu/arm926ejs/start.S >>> @@ -105,9 +105,9 @@ flush_dcache: >>> /* >>> * Go setup Memory and board specific bits prior to relocation. >>> */ >>> - mov ip, lr /* perserve link reg across call */ >>> + mov r4, lr /* perserve link reg across call */ >>> bl lowlevel_init /* go setup pll,mux,memory */ >>> - mov lr, ip /* restore link */ >>> + mov lr, r4 /* restore link */ >>> #endif >>> mov pc, lr /* back to my caller */ >>> #endif /* CONFIG_SKIP_LOWLEVEL_INIT */ >>> > >> Applied to u-boot-imx, thanks ! > > I think this might be causing me a problem on a Marvell Kirkwood board I'm > working on getting into upstream. It may also be problematic for orion5x > boards. Both of these use r4 in lowlevel_init. > > Obviously I can fix the board that I'm working on. Is there some > expectation as to which registers can be clobbered?
The "Procedure Call Standard for the ARM® Architecture” may help: http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042f/IHI0042F_aapcs.pdf Page 15 A subroutine must preserve the contents of the registers r4-r8, r10, r11 and SP (and r9 in PCS variants that designate r9 as v6). So for thumb r1-r3 and r12 should be usable without taking any care of them. Maybe r13 depending if you already have a stack or not. Regards, Klaus _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot
