Messages in this thread | | | Date | Fri, 14 Jan 2011 10:24:52 -0600 | Subject | Re: [PATCH] ARM: vfp: Fix up exception location in Thumb mode | From | Dave Martin <> |
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Hi,
On Fri, Jan 14, 2011 at 8:10 AM, Catalin Marinas <catalin.marinas@arm.com> wrote: > On Fri, 2011-01-14 at 12:02 +0000, Russell King - ARM Linux wrote: >> On Fri, Jan 14, 2011 at 11:43:04AM +0000, Catalin Marinas wrote: >> > > pr_debug("VFP: bounce: trigger %08x fpexc %08x\n", trigger, fpexc); >> > > >> > > /* >> > > + * If the exception occured in thumb mode, pc is exception location + 2, >> > > + * the middle of the 32-bit VFP instruction. Add 2 to get exception >> > > + * location + 4, the same we get in ARM mode. >> > > + */ >> > > +#ifdef CONFIG_ARM_THUMB >> > > + if (regs->ARM_cpsr & PSR_T_BIT) >> > > + regs->ARM_pc += 2; >> > > +#endif >> > >> > You can use "if (thumb_mode(regs))" and avoid the #ifdef entirely. >> >> I don't think this is correct. On entry to the undefined instruction >> handler, we get the uncorrected PC value, so PC points to the >> instruction after the faulting instruction. >> >> If it was an ARM instruction, that is located at PC-4. If it was a >> Thumb instruction, it is located at PC-2. This PC value is passed >> unmodified to the VFP entry code, and the passed r2 reflect the >> value in regs->ARM_pc. > > The entry-armv.S code adds 2 to the r2 register in case of a 32-bit > Thumb instruction, so it is no longer the same as the ARM_pc. > > Since the VFP instructions in Thumb mode are always 32-bit, Colin's > patch made sense to me.
Is the comment preceding __und_usr_unknown causing some confusion here?
/* * The FP module is called with these registers set: * r0 = instruction * r2 = PC+4 ...
That reflects the ARM case only: for Thumb, r2 is always PC+2 (?)
The comment at the start of do_undefinstr() (which receives these registers) is correct though:
/* * According to the ARM ARM, PC is 2 or 4 bytes ahead, * depending whether we're in Thumb mode or not. * Correct this offset.
Cheers ---Dave -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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