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[34.125.52.154]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-128e7cb5208sm6853358c88.9.2026.03.11.16.05.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Mar 2026 16:05:26 -0700 (PDT) Date: Wed, 11 Mar 2026 23:05:22 +0000 From: Carlos Llamas To: Sami Tolvanen Cc: Kees Cook , Peter Zijlstra , Sean Christopherson , LKML , linux-arm-kernel , kvmarm , kvm@vger.kernel.org, Will McVicker Subject: Re: [PATCH v4 09/17] perf/core: Use static_call to optimize perf_guest_info_callbacks Message-ID: References: <20211111020738.2512932-1-seanjc@google.com> <20211111020738.2512932-10-seanjc@google.com> <202202061011.A255DE55B@keescook> <202202061854.B5B11282@keescook> <20260309223156.GA73501@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260309223156.GA73501@google.com> On Mon, Mar 09, 2026 at 10:31:56PM +0000, Sami Tolvanen wrote: > Hi Carlos, > > If you need a stub with a matching CFI type for an arbitrary function, > perhaps you can do something like this (arm64, untested): > > #define DEFINE_TYPED_STUB_RET0(name, reffunc) \ > typeof(reffunc) name; \ > __ADDRESSABLE(name); \ > asm( \ > " " __ALIGN_STR " \n" \ > " .4byte __kcfi_typeid_" #name " \n" \ > #name ": \n" \ > " bti c \n" \ > " mov x0, xzr \n" \ > " ret " \ > ) > > For the !CONFIG_CFI case, or architectures that implement static calls, > you can probably just point the stub to __static_call_return0: > > #define DEFINE_TYPED_STUB_RET0(name, reffunc) \ > typeof(reffunc) name __asm__("__static_call_return0") > > Sami Alright, I've sent out a patch for this here: https://lore.kernel.org/all/20260311225822.1565895-1-cmllamas@google.com/ It might seem "incomplete" because it only handles the RET0 case and it doesn't export the stubs either. However, I didn't find any static_calls for which the lack of these things would be an issue. I can address such things in a v2 if really needed though. Cheers, -- Carlos Llamas