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Mon, 25 Oct 2021 10:19:05 -0700 (PDT) Subject: Re: [RFC 1/2] tls: add macros for coroutine-safe TLS variables To: Stefan Hajnoczi , qemu-devel@nongnu.org References: <20211025140716.166971-1-stefanha@redhat.com> <20211025140716.166971-2-stefanha@redhat.com> From: Richard Henderson Message-ID: Date: Mon, 25 Oct 2021 10:19:04 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <20211025140716.166971-2-stefanha@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::635; envelope-from=richard.henderson@linaro.org; helo=mail-pl1-x635.google.com X-Spam_score_int: -48 X-Spam_score: -4.9 X-Spam_bar: ---- X-Spam_report: (-4.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-2.846, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: fweimer@redhat.com, Kevin Wolf , thuth@redhat.com, qemu-block@nongnu.org, Fam Zheng , sguelton@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 10/25/21 7:07 AM, Stefan Hajnoczi wrote: > Compiler optimizations can cache TLS values across coroutine yield > points, resulting in stale values from the previous thread when a > coroutine is re-entered by a new thread. ... > include/qemu/tls.h | 142 +++++++++++++++++++++++++++++++++++++++++++++ Better as qemu/coroutine-tls.h, since it is needed for no other purpose. > +#define QEMU_DEFINE_TLS(type, var) \ > + __thread type qemu_tls_##var; \ > + type get_##var(void) { return qemu_tls_##var; } \ > + void set_##var(type v) { qemu_tls_##var = v; } You might as well make the variable static, since it may only be referenced by these two functions. > +#define QEMU_DEFINE_STATIC_TLS(type, var) \ > + static __thread type qemu_tls_##var; \ > + static __attribute__((noinline)) type get_##var(void); \ > + static type get_##var(void) { return qemu_tls_##var; } \ > + static __attribute__((noinline)) void set_##var(type v); \ > + static void set_##var(type v) { qemu_tls_##var = v; } You don't need separate function declarations; you can fold them together. If would be nice to inline this when possible, #if defined(__aarch64__) #define QEMU_COROUTINE_TLS_ADDR(RET, VAR) \ asm volatile("mrs %0, tpidr_el0\n\t" \ "add %0, %0, #:tprel_hi12:"#VAR", lsl #12\n\t" \ "add %0, %0, #:tprel_lo12_nc:"#VAR \ : "=r"(RET)) #elif defined(__powerpc64__) #define QEMU_COROUTINE_TLS_ADDR(RET, VAR) \ asm volatile("addis %0,13,"#VAR"@tprel@ha\n\t" \ "add %0,%0,"#VAR"@tprel@l" \ : "=r"(RET)) #elif defined(__riscv) #define QEMU_COROUTINE_TLS_ADDR(RET, VAR) \ asm volatile("lui %0,%%tprel_hi("#VAR")\n\t" \ "add %0,%0,%%tprel_add("#VAR")\n\t" \ "addi %0,%0,%%tprel_lo("#VAR")" \ : "=r"(RET)) #elif defined(__x86_64__) #define QEMU_COROUTINE_TLS_ADDR(RET, VAR) \ asm volatile("mov %%fs:"#VAR"@tpoff, %0" : "=r"(RET)) #endif #ifdef QEMU_COROUTINE_TLS_ADDR #define QEMU_COROUTINE_TLS_DECLARE(TYPE, VAR) \ extern __thread TYPE co_tls_##VAR; \ static inline TYPE get_##VAR(void) \ { TYPE *p; QEMU_COROUTINE_TLS_ADDR(p, co_tls_##VAR); return *p; } \ static inline void set_##VAR(TYPE v) \ { TYPE *p; QEMU_COROUTINE_TLS_ADDR(p, co_tls_##VAR); *p = v; } #else etc #endif r~