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X-Received-From: 2607:f8b0:4864:20::343 Subject: Re: [Qemu-devel] [PATCH] tcg/aarch64: Fix output of extract2 opcodes X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , QEMU Developers , Beata Michalska Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 7/10/19 8:12 PM, Aleksandar Markovic wrote: > On Tue, Jul 9, 2019 at 8:56 PM Richard Henderson > wrote: >> >> The aarch64 argument ordering for the operands is big-endian, >> whereas the tcg argument ordering is little-endian. Use REG0 >> so that we honor the rZ constraints. > > Hello, Richard. > > If endian and rZ constraints are unrelated problems, then I think the > commit message > should be: > > "This patch fixes two problem: > > - endianness: the aarch64 argument ordering for the operands is > big-endian, whereas the tcg argument ordering is little-endian. > > - rZ constrains: REG0() macro should be applied to the affected > arguments." That's fair. > One could argue that in this case the patch this should be actually two patches. > This is better because of bisectability. The number of line in the > patch doesn't matter. Well, nothing between the faulty commit (Fixes: 464c2969d5d) and the second of the two prospective patches is really bisectable. For the given test case, all points in between will fail at runtime, even if each point compiles. Therefore I don't see the point in separating the two changes. > Would you be so kind to consider my opinion? Yes. Thanks for the expanded opinion. I plan to change the commit message to: --- tcg/aarch64: Fix output of extract2 opcodes This patch fixes two problems: (1) The inputs to the EXTR insn were reversed, (2) The input constraints use rZ, which means that we need to use the REG0 macro in order to supply XZR for a constant 0 input. r-b, s-o-b, etc --- Does that seem sufficient to you? r~