From: Linus Torvalds <torvalds@linux-foundation.org> To: Will Deacon <will@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org>, Michael Ellerman <mpe@ellerman.id.au>, Daniel Axtens <dja@axtens.net>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linuxppc-dev <linuxppc-dev@lists.ozlabs.org>, Christophe Leroy <christophe.leroy@c-s.fr>, linux-arch <linux-arch@vger.kernel.org>, Mark Rutland <mark.rutland@arm.com>, Segher Boessenkool <segher@kernel.crashing.org>, Arnd Bergmann <arnd@arndb.de>, Christian Borntraeger <borntraeger@de.ibm.com> Subject: Re: READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops)) Date: Tue, 17 Dec 2019 10:32:35 -0800 [thread overview] Message-ID: <CAHk-=wjNLxSZZs+A0tyb-MnJ2YU-sqTAfy0-X+9vxjXfs_O4zA@mail.gmail.com> (raw) In-Reply-To: <CAHk-=whBnZBVNwu8aVVp205EKk7xtsnQgSjs38a5=y9HyheXzQ@mail.gmail.com> [-- Attachment #1: Type: text/plain, Size: 755 bytes --] On Tue, Dec 17, 2019 at 10:04 AM Linus Torvalds <torvalds@linux-foundation.org> wrote: > > Let me think about it. How about we just get rid of the union entirely, and just use 'unsigned long' or 'unsigned long long' depending on the size. Something like the attached patch - it still requires that it be an arithmetic type, but now because of the final cast. But it might still be a cast to a volatile type, of course. Then the result will be volatile, but at least now READ_ONCE() won't be taking the address of a volatile variable on the stack - does that at least fix some of the horrible code generation. Hmm? This is untested, because I obviously still have the cases of structures (page table entries) being accessed once.. Linus [-- Attachment #2: patch.diff --] [-- Type: text/x-patch, Size: 2149 bytes --] include/linux/compiler.h | 33 +++++++++++++++++---------------- 1 file changed, 17 insertions(+), 16 deletions(-) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 5e88e7e33abe..8b4282194f16 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -179,18 +179,18 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, #include <uapi/linux/types.h> -#define __READ_ONCE_SIZE \ -({ \ - switch (size) { \ - case 1: *(__u8 *)res = *(volatile __u8 *)p; break; \ - case 2: *(__u16 *)res = *(volatile __u16 *)p; break; \ - case 4: *(__u32 *)res = *(volatile __u32 *)p; break; \ - case 8: *(__u64 *)res = *(volatile __u64 *)p; break; \ - default: \ - barrier(); \ - __builtin_memcpy((void *)res, (const void *)p, size); \ - barrier(); \ - } \ +/* "unsigned long" or "unsigned long long" - make it fit in a register if possible */ +#define __READ_ONCE_TYPE(size) \ + __typeof__(__builtin_choose_expr(size > sizeof(0UL), 0ULL, 0UL)) + +#define __READ_ONCE_SIZE \ +({ \ + switch (size) { \ + case 1: *(unsigned long *)res = *(volatile __u8 *)p; break; \ + case 2: *(unsigned long *)res = *(volatile __u16 *)p; break; \ + case 4: *(unsigned long *)res = *(volatile __u32 *)p; break; \ + case 8: *(unsigned long long *)res = *(volatile __u64 *)p; break; \ + } \ }) static __always_inline @@ -258,13 +258,14 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s #define __READ_ONCE(x, check) \ ({ \ - union { typeof(x) __val; char __c[1]; } __u; \ + __READ_ONCE_TYPE(sizeof(x)) __u; \ + compiletime_assert(sizeof(x) <= sizeof(__u), "READ_ONCE type"); \ if (check) \ - __read_once_size(&(x), __u.__c, sizeof(x)); \ + __read_once_size(&(x), &__u, sizeof(x)); \ else \ - __read_once_size_nocheck(&(x), __u.__c, sizeof(x)); \ + __read_once_size_nocheck(&(x), &__u, sizeof(x)); \ smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \ - __u.__val; \ + (__typeof__(x))__u; \ }) #define READ_ONCE(x) __READ_ONCE(x, 1)
WARNING: multiple messages have this Message-ID (diff)
From: Linus Torvalds <torvalds@linux-foundation.org> To: Will Deacon <will@kernel.org> Cc: linux-arch <linux-arch@vger.kernel.org>, Arnd Bergmann <arnd@arndb.de>, Peter Zijlstra <peterz@infradead.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Christian Borntraeger <borntraeger@de.ibm.com>, Mark Rutland <mark.rutland@arm.com>, linuxppc-dev <linuxppc-dev@lists.ozlabs.org>, Daniel Axtens <dja@axtens.net> Subject: Re: READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops)) Date: Tue, 17 Dec 2019 10:32:35 -0800 [thread overview] Message-ID: <CAHk-=wjNLxSZZs+A0tyb-MnJ2YU-sqTAfy0-X+9vxjXfs_O4zA@mail.gmail.com> (raw) In-Reply-To: <CAHk-=whBnZBVNwu8aVVp205EKk7xtsnQgSjs38a5=y9HyheXzQ@mail.gmail.com> [-- Attachment #1: Type: text/plain, Size: 755 bytes --] On Tue, Dec 17, 2019 at 10:04 AM Linus Torvalds <torvalds@linux-foundation.org> wrote: > > Let me think about it. How about we just get rid of the union entirely, and just use 'unsigned long' or 'unsigned long long' depending on the size. Something like the attached patch - it still requires that it be an arithmetic type, but now because of the final cast. But it might still be a cast to a volatile type, of course. Then the result will be volatile, but at least now READ_ONCE() won't be taking the address of a volatile variable on the stack - does that at least fix some of the horrible code generation. Hmm? This is untested, because I obviously still have the cases of structures (page table entries) being accessed once.. Linus [-- Attachment #2: patch.diff --] [-- Type: text/x-patch, Size: 2149 bytes --] include/linux/compiler.h | 33 +++++++++++++++++---------------- 1 file changed, 17 insertions(+), 16 deletions(-) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 5e88e7e33abe..8b4282194f16 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -179,18 +179,18 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, #include <uapi/linux/types.h> -#define __READ_ONCE_SIZE \ -({ \ - switch (size) { \ - case 1: *(__u8 *)res = *(volatile __u8 *)p; break; \ - case 2: *(__u16 *)res = *(volatile __u16 *)p; break; \ - case 4: *(__u32 *)res = *(volatile __u32 *)p; break; \ - case 8: *(__u64 *)res = *(volatile __u64 *)p; break; \ - default: \ - barrier(); \ - __builtin_memcpy((void *)res, (const void *)p, size); \ - barrier(); \ - } \ +/* "unsigned long" or "unsigned long long" - make it fit in a register if possible */ +#define __READ_ONCE_TYPE(size) \ + __typeof__(__builtin_choose_expr(size > sizeof(0UL), 0ULL, 0UL)) + +#define __READ_ONCE_SIZE \ +({ \ + switch (size) { \ + case 1: *(unsigned long *)res = *(volatile __u8 *)p; break; \ + case 2: *(unsigned long *)res = *(volatile __u16 *)p; break; \ + case 4: *(unsigned long *)res = *(volatile __u32 *)p; break; \ + case 8: *(unsigned long long *)res = *(volatile __u64 *)p; break; \ + } \ }) static __always_inline @@ -258,13 +258,14 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s #define __READ_ONCE(x, check) \ ({ \ - union { typeof(x) __val; char __c[1]; } __u; \ + __READ_ONCE_TYPE(sizeof(x)) __u; \ + compiletime_assert(sizeof(x) <= sizeof(__u), "READ_ONCE type"); \ if (check) \ - __read_once_size(&(x), __u.__c, sizeof(x)); \ + __read_once_size(&(x), &__u, sizeof(x)); \ else \ - __read_once_size_nocheck(&(x), __u.__c, sizeof(x)); \ + __read_once_size_nocheck(&(x), &__u, sizeof(x)); \ smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \ - __u.__val; \ + (__typeof__(x))__u; \ }) #define READ_ONCE(x) __READ_ONCE(x, 1)
next prev parent reply other threads:[~2019-12-17 18:32 UTC|newest] Thread overview: 86+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-12-06 12:46 [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops) Michael Ellerman 2019-12-06 12:46 ` Michael Ellerman 2019-12-06 13:16 ` Peter Zijlstra 2019-12-06 13:16 ` Peter Zijlstra 2019-12-10 5:38 ` Michael Ellerman 2019-12-10 5:38 ` Michael Ellerman 2019-12-10 10:15 ` Peter Zijlstra 2019-12-10 10:15 ` Peter Zijlstra 2019-12-11 0:29 ` Michael Ellerman 2019-12-11 0:29 ` Michael Ellerman 2019-12-12 5:42 ` READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops)) Michael Ellerman 2019-12-12 5:42 ` Michael Ellerman 2019-12-12 8:01 ` Peter Zijlstra 2019-12-12 8:01 ` Peter Zijlstra 2019-12-12 10:07 ` Will Deacon 2019-12-12 10:07 ` Will Deacon 2019-12-12 10:46 ` Peter Zijlstra 2019-12-12 10:46 ` Peter Zijlstra 2019-12-12 17:04 ` Will Deacon 2019-12-12 17:04 ` Will Deacon 2019-12-12 17:16 ` Will Deacon 2019-12-12 17:16 ` Will Deacon 2019-12-12 17:41 ` Linus Torvalds 2019-12-12 17:41 ` Linus Torvalds 2019-12-12 17:50 ` Segher Boessenkool 2019-12-12 17:50 ` Segher Boessenkool 2019-12-12 18:06 ` Will Deacon 2019-12-12 18:06 ` Will Deacon 2019-12-12 18:29 ` Christian Borntraeger 2019-12-12 18:29 ` Christian Borntraeger 2019-12-12 18:43 ` Linus Torvalds 2019-12-12 18:43 ` Linus Torvalds 2019-12-12 19:34 ` Will Deacon 2019-12-12 19:34 ` Will Deacon 2019-12-12 20:21 ` Peter Zijlstra 2019-12-12 20:21 ` Peter Zijlstra 2019-12-12 20:53 ` Peter Zijlstra 2019-12-12 20:53 ` Peter Zijlstra 2019-12-13 10:47 ` Luc Van Oostenryck 2019-12-13 10:47 ` Luc Van Oostenryck 2019-12-13 12:56 ` Peter Zijlstra 2019-12-13 12:56 ` Peter Zijlstra 2019-12-13 14:28 ` Luc Van Oostenryck 2019-12-13 14:28 ` Luc Van Oostenryck 2019-12-12 20:49 ` Linus Torvalds 2019-12-12 20:49 ` Linus Torvalds 2019-12-13 13:17 ` Arnd Bergmann 2019-12-13 13:17 ` Arnd Bergmann 2019-12-13 21:32 ` Arnd Bergmann 2019-12-13 21:32 ` Arnd Bergmann 2019-12-13 22:01 ` Linus Torvalds 2019-12-13 22:01 ` Linus Torvalds 2019-12-16 10:28 ` Will Deacon 2019-12-16 10:28 ` Will Deacon 2019-12-16 11:47 ` Peter Zijlstra 2019-12-16 11:47 ` Peter Zijlstra 2019-12-16 12:06 ` Arnd Bergmann 2019-12-16 12:06 ` Arnd Bergmann 2019-12-17 17:07 ` Will Deacon 2019-12-17 17:07 ` Will Deacon 2019-12-17 18:04 ` Linus Torvalds 2019-12-17 18:04 ` Linus Torvalds 2019-12-17 18:05 ` Linus Torvalds 2019-12-17 18:05 ` Linus Torvalds 2019-12-17 18:31 ` Will Deacon 2019-12-17 18:31 ` Will Deacon 2019-12-17 18:32 ` Linus Torvalds [this message] 2019-12-17 18:32 ` Linus Torvalds 2019-12-18 12:17 ` Michael Ellerman 2019-12-18 12:17 ` Michael Ellerman 2019-12-19 12:11 ` Will Deacon 2019-12-19 12:11 ` Will Deacon 2019-12-18 10:22 ` Christian Borntraeger 2019-12-18 10:22 ` Christian Borntraeger 2019-12-18 10:35 ` Will Deacon 2019-12-18 10:35 ` Will Deacon 2019-12-13 12:07 ` Michael Ellerman 2019-12-13 12:07 ` Michael Ellerman 2019-12-13 13:53 ` Segher Boessenkool 2019-12-13 13:53 ` Segher Boessenkool 2019-12-13 21:06 ` Michael Ellerman 2019-12-13 21:06 ` Michael Ellerman 2019-12-12 15:10 ` Segher Boessenkool 2019-12-12 15:10 ` Segher Boessenkool 2019-12-06 22:15 ` [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops) pr-tracker-bot 2019-12-06 22:15 ` pr-tracker-bot
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to='CAHk-=wjNLxSZZs+A0tyb-MnJ2YU-sqTAfy0-X+9vxjXfs_O4zA@mail.gmail.com' \ --to=torvalds@linux-foundation.org \ --cc=arnd@arndb.de \ --cc=borntraeger@de.ibm.com \ --cc=christophe.leroy@c-s.fr \ --cc=dja@axtens.net \ --cc=linux-arch@vger.kernel.org \ --cc=linux-kernel@vger.kernel.org \ --cc=linuxppc-dev@lists.ozlabs.org \ --cc=mark.rutland@arm.com \ --cc=mpe@ellerman.id.au \ --cc=peterz@infradead.org \ --cc=segher@kernel.crashing.org \ --cc=will@kernel.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.