On 04/18/2018 06:25 PM, Klaus Goger wrote: > When building the mxs platform in thumb mode gcc generates code using > the intra procedure call scratch register (ip/r12) for the calling the > lowlevel_init function. This modifies the lr in flush_dcache which > causes u-boot proper to end in an endless loop. > > 40002334: e1a0c00e mov ip, lr > 40002338: eb00df4c bl 4003a070 > <__lowlevel_init_from_arm> > 4000233c: e1a0e00c mov lr, ip > 40002340: e1a0f00e mov pc, lr > [...] > 4003a070 <__lowlevel_init_from_arm>: > 4003a070: e59fc004 ldr ip, [pc, #4] ; 4003a07c > <__lowlevel_init_from_arm+0xc> > 4003a074: e08fc00c add ip, pc, ip > 4003a078: e12fff1c bx ip > 4003a07c: fffc86cd .word 0xfffc86cd > > Instead of using the the ip/r12 register we use sl/r10 to preserve the > link register. > > According to "Procedure Call Standard for the ARM Architecture" by ARM > subroutines have to preserve the contents of register r4-r8, r10, r11 > and SP. So using r10 instead of r12 should be save. > > Signed-off-by: Klaus Goger <klaus.go...@theobroma-systems.com> > Signed-off-by: Christoph Muellner <christoph.muell...@theobroma-systems.com> > > --- > > arch/arm/cpu/arm926ejs/start.S | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/arch/arm/cpu/arm926ejs/start.S b/arch/arm/cpu/arm926ejs/start.S > index 959d1ed86d..103bd15914 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 */ > - bl lowlevel_init /* go setup pll,mux,memory */ > - mov lr, ip /* restore link */ > + mov sl, lr /* perserve link reg across call */ > + blx lowlevel_init /* go setup pll,mux,memory */ > + mov lr, sl /* restore link */ > #endif > - mov pc, lr /* back to my caller */ > + bx lr /* back to my caller */ > #endif /* CONFIG_SKIP_LOWLEVEL_INIT */
Are you sure this doesn't break the non-thumb operation ? Also, is this really MXS specific or not ? -- Best regards, Marek Vasut _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot
