Messages in this thread Patch in this message | | | Date | Wed, 9 Apr 2014 17:01:09 +0100 | From | Russell King - ARM Linux <> | Subject | Re: [PATCH] ARM: reinsert ARCH_MULTI_V4 Kconfig option |
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On Wed, Apr 09, 2014 at 05:50:57PM +0200, Arnd Bergmann wrote: > On Wednesday 09 April 2014 16:27:11 Russell King - ARM Linux wrote: > > If it's called from ARM code, then \reg will contain a 4-byte aligned > > address. If it's called from Thumb code, \reg will contain a 2-byte > > aligned address with bit 0 *always* set. > > Right, that is the assumption. > > > So, with the code originally quoted above, if the helper is called from > > thumb code, and CONFIG_CPU_32v4 is enabled, then we end up falling past > > the moveq to the "b ." and entering an infinite loop. > > As Uwe said, that "b ." was not meant to be in the patch used for > submission, it was to check what goes wrong when running this code > on ARMv4 -- either crash user space or hang in an infinite loop. > I forgot what the result of that experiment was. > > The trouble is that this code: > > .macro usr_ret, reg > #ifdef CONFIG_ARM_THUMB > #ifdef CONFIG_CPU_32v4 > tst \reg, #3 > moveq pc, \reg > #endif > bx \reg > #else > mov pc, \reg > #endif > .endm > > for some reason does the wrong thing running on ARMv4 (fa526) with non-thumb > user space when both CONFIG_CPU_32v4 and CONFIG_ARM_THUMB are enabled: > it still tries to do the 'bx' and triggers an invalid opcode exception.
I assume this has been discussed in off-list (maybe on some irc channel somewhere), because there's nothing on-list apart from these emails...
So, let's repeat the debugging which probably has already occured, but this time on-list...
It would be useful to see the register state from the undefined instruction exception. That needs this patch, CONFIG_DEBUG_USER in the kernel config enabled, and user_debug=1 passed on the kernel command line.
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c index 172ee18ff124..abd2fc067736 100644 --- a/arch/arm/kernel/traps.c +++ b/arch/arm/kernel/traps.c @@ -445,6 +445,7 @@ asmlinkage void __exception do_undefinstr(struct pt_regs *regs) if (user_debug & UDBG_UNDEFINED) { printk(KERN_INFO "%s (%d): undefined instruction: pc=%p\n", current->comm, task_pid_nr(current), pc); + __show_regs(regs); dump_instr(KERN_INFO, regs); } #endif
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