From: Russell King - ARM Linux <linux@arm.linux.org.uk> To: Catalin Marinas <catalin.marinas@arm.com> Cc: Colin Cross <ccross@android.com>, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] ARM: vfp: Fix up exception location in Thumb mode Date: Fri, 14 Jan 2011 15:49:19 +0000 [thread overview] Message-ID: <20110114154919.GE15996@n2100.arm.linux.org.uk> (raw) In-Reply-To: <1295014231.7901.41.camel@e102109-lin.cambridge.arm.com> On Fri, Jan 14, 2011 at 02:10:31PM +0000, Catalin Marinas wrote: > On Fri, 2011-01-14 at 12:02 +0000, Russell King - ARM Linux wrote: > > 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. That's something that should be fixed - the entry conditions should be the same irrespective of thumb or arm encoding. > Since the VFP instructions in Thumb mode are always 32-bit, Colin's > patch made sense to me. I looked up the VADD instruction in the ARM ARM. It has both a 16-bit and 32-bit encoding. > > 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. At the moment its just confusing as things stand, as some things are changed in one place and not the other. Let's kill the pointless addition of 2 in the undefined instruction handler so that in every case we enter handlers with r2 == regs->ARM_pc, and regs->ARM_pc as per the ARM ARM undefined exception entry LR. Undefined instruction exception handlers can then rely on the meaning of both of these.
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From: linux@arm.linux.org.uk (Russell King - ARM Linux) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH] ARM: vfp: Fix up exception location in Thumb mode Date: Fri, 14 Jan 2011 15:49:19 +0000 [thread overview] Message-ID: <20110114154919.GE15996@n2100.arm.linux.org.uk> (raw) In-Reply-To: <1295014231.7901.41.camel@e102109-lin.cambridge.arm.com> On Fri, Jan 14, 2011 at 02:10:31PM +0000, Catalin Marinas wrote: > On Fri, 2011-01-14 at 12:02 +0000, Russell King - ARM Linux wrote: > > 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. That's something that should be fixed - the entry conditions should be the same irrespective of thumb or arm encoding. > Since the VFP instructions in Thumb mode are always 32-bit, Colin's > patch made sense to me. I looked up the VADD instruction in the ARM ARM. It has both a 16-bit and 32-bit encoding. > > 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. At the moment its just confusing as things stand, as some things are changed in one place and not the other. Let's kill the pointless addition of 2 in the undefined instruction handler so that in every case we enter handlers with r2 == regs->ARM_pc, and regs->ARM_pc as per the ARM ARM undefined exception entry LR. Undefined instruction exception handlers can then rely on the meaning of both of these.
next prev parent reply other threads:[~2011-01-14 15:49 UTC|newest] Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-01-14 7:42 [PATCH] ARM: vfp: Fix up exception location in Thumb mode Colin Cross 2011-01-14 7:42 ` Colin Cross 2011-01-14 11:43 ` Catalin Marinas 2011-01-14 11:43 ` Catalin Marinas 2011-01-14 12:02 ` Russell King - ARM Linux 2011-01-14 12:02 ` Russell King - ARM Linux 2011-01-14 14:10 ` Catalin Marinas 2011-01-14 14:10 ` Catalin Marinas 2011-01-14 15:49 ` Russell King - ARM Linux [this message] 2011-01-14 15:49 ` Russell King - ARM Linux 2011-01-14 16:23 ` Catalin Marinas 2011-01-14 16:23 ` Catalin Marinas 2011-01-14 16:35 ` Russell King - ARM Linux 2011-01-14 16:35 ` Russell King - ARM Linux 2011-01-14 16:58 ` Catalin Marinas 2011-01-14 16:58 ` Catalin Marinas 2011-01-14 17:30 ` Russell King - ARM Linux 2011-01-14 17:30 ` Russell King - ARM Linux 2011-01-14 18:47 ` Russell King - ARM Linux 2011-01-14 18:47 ` Russell King - ARM Linux 2011-01-14 19:23 ` Colin Cross 2011-01-14 19:23 ` Colin Cross 2011-01-14 19:51 ` Colin Cross 2011-01-14 19:51 ` Colin Cross 2011-01-14 21:24 ` Russell King - ARM Linux 2011-01-14 21:24 ` Russell King - ARM Linux 2011-01-25 23:33 ` Colin Cross 2011-01-25 23:33 ` Colin Cross 2011-01-26 11:26 ` Russell King - ARM Linux 2011-01-26 11:26 ` Russell King - ARM Linux 2011-01-27 6:11 ` Colin Cross 2011-01-27 6:11 ` Colin Cross 2011-01-27 6:35 ` Colin Cross 2011-01-27 6:35 ` Colin Cross 2011-01-27 7:30 ` Colin Cross 2011-01-27 7:30 ` Colin Cross 2011-02-09 18:12 ` Colin Cross 2011-02-09 18:12 ` Colin Cross 2011-01-15 15:38 ` Catalin Marinas 2011-01-15 15:38 ` Catalin Marinas 2011-01-15 15:43 ` Russell King - ARM Linux 2011-01-15 15:43 ` Russell King - ARM Linux 2011-01-16 11:51 ` Catalin Marinas 2011-01-16 11:51 ` Catalin Marinas 2011-01-15 15:31 ` Catalin Marinas 2011-01-15 15:31 ` Catalin Marinas 2011-01-15 15:40 ` Russell King - ARM Linux 2011-01-15 15:40 ` Russell King - ARM Linux 2011-01-16 11:49 ` Catalin Marinas 2011-01-16 11:49 ` Catalin Marinas 2011-01-23 15:51 ` Russell King - ARM Linux 2011-01-23 15:51 ` Russell King - ARM Linux 2011-01-25 13:19 ` Catalin Marinas 2011-01-25 13:19 ` Catalin Marinas 2011-01-16 21:25 ` Catalin Marinas 2011-01-16 21:25 ` Catalin Marinas 2011-01-23 15:46 ` Russell King - ARM Linux 2011-01-23 15:46 ` Russell King - ARM Linux 2011-01-25 13:45 ` Catalin Marinas 2011-01-25 13:45 ` Catalin Marinas 2011-01-14 16:24 ` Dave Martin 2011-01-14 16:24 ` Dave Martin 2011-01-14 16:52 ` Russell King - ARM Linux 2011-01-14 16:52 ` Russell King - ARM Linux
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