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charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable X-Content-Filtered-By: Mailman/MimeDel 2.1.29 X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 06 May 2021 17:31:47 -0000 Hi Naohiro, > I've read the mail thread regarding BTI, but I think I couldn't fully und= erstand the > problem. BTI seems available from ARMv8.5, and A64FX is ARMv8.2. BTI instructions are NOP hints, so it is possible to enable BTI even on ARM= v8.0. Using BTI instructions is harmless on CPUs that don't support it if NOP hin= ts are as cheap as a NOP (which generally doesn't need any execution resources). > Even though distro distributed BTI enabled binary, BTI doesn't work on A6= 4FX. It works (ie. it is binary compatible with A64FX) and should have no effect= . However it seems to cause an unexpected slowdown. > So BTI_J macro can be removed from A64FX IFUNC code at least, because A64= FX > IFUNC code is executed only on A64FX. How is removing it just from memcpy going to help? The worry is not about m= emcpy but the slowdown from all the BTI instructions that will be added to most f= unctions. Note it is still worthwhile to change BTI_C to NOP as suggested - that is t= he case when BTI is not enabled, and there you want to avoid inserting BTI when it is no= t needed. Cheers, Wilco