From mboxrd@z Thu Jan 1 00:00:00 1970 From: catalin.marinas@arm.com (Catalin Marinas) Date: Fri, 14 Jan 2011 14:10:31 +0000 Subject: [PATCH] ARM: vfp: Fix up exception location in Thumb mode In-Reply-To: <20110114120229.GA15996@n2100.arm.linux.org.uk> References: <1294990949-2729-1-git-send-email-ccross@android.com> <20110114120229.GA15996@n2100.arm.linux.org.uk> Message-ID: <1295014231.7901.41.camel@e102109-lin.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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. > I think that the undefined instruction handling needs reworking for > Thumb entirely as we could be dealing with a 16-bit or 32-bit thumb > instruction, and we have no way of knowing without repeatedly > decoding that instruction. We already handle the r2 for in __und_usr. We don't deal with ARM_pc but we could either do it in __und_usr or let the code handling the undef fix it up. -- Catalin