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Date: Wed, 3 May 2017 11:51:56 +0100 From: Mark Rutland <mark.rutland@....com> To: Matthias Kaehlcke <mka@...omium.org> Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Christoffer Dall <christoffer.dall@...aro.org>, Marc Zyngier <marc.zyngier@....com>, Vladimir Murzin <vladimir.murzin@....com>, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, Grant Grundler <grundler@...omium.org>, Greg Hackmann <ghackmann@...gle.com>, Michael Davidson <md@...gle.com> Subject: Re: [PATCH] arm64: Fix multiple 'asm-operand-widths' warnings On Tue, May 02, 2017 at 11:52:12AM -0700, Matthias Kaehlcke wrote: > El Tue, May 02, 2017 at 06:29:48PM +0100 Mark Rutland ha dit: > > On Mon, May 01, 2017 at 02:26:22PM -0700, Matthias Kaehlcke wrote: > > > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h > > > index 5308d696311b..7db143689694 100644 > > > --- a/arch/arm64/include/asm/uaccess.h > > > +++ b/arch/arm64/include/asm/uaccess.h > > > @@ -302,7 +302,7 @@ do { \ > > > " .previous\n" \ > > > _ASM_EXTABLE(1b, 3b) \ > > > : "+r" (err) \ > > > - : "r" (x), "r" (addr), "i" (-EFAULT)) > > > + : "r" ((__u64)x), "r" (addr), "i" (-EFAULT)) > > > > > > > For reference, do you have the warning for this case to hand? > > > > In __put_user_err() we make __pu_val the same type as *ptr, then we > > switch on sizeof(*ptr), and pass __pu_val to __put_user_asm(), as x. > > For cases 1, 2, and 4, we use "%w" as the register template. > > > > So I can't see why we'd need this cast in __put_user_err(). > > > > I must be missing something. > > This is one of many instances: > > ./include/linux/pagemap.h:554:10: warning: value size does not match register size specified by the constraint and modifier [-Wasm-operand-widths] > return __put_user(0, end); > ^ > ./arch/arm64/include/asm/uaccess.h:338:2: note: expanded from macro '__put_user' > __put_user_err((x), (ptr), __pu_err); \ > ^ > ./arch/arm64/include/asm/uaccess.h:326:38: note: expanded from macro '__put_user_err' > __put_user_asm("str", "sttr", "%", __pu_val, (ptr), \ > ^ > ./include/linux/pagemap.h:554:10: note: use constraint modifier "w" > ./arch/arm64/include/asm/uaccess.h:338:2: note: expanded from macro '__put_user' > __put_user_err((x), (ptr), __pu_err); \ > ^ > ./arch/arm64/include/asm/uaccess.h:326:34: note: expanded from macro '__put_user_err' > __put_user_asm("str", "sttr", "%", __pu_val, (ptr), \ > ^ Thanks for the log above! > 'end' is a char pointer, it is not clear to me why we would end up in > the width == 8 branch. Indeed. I took a look, and I think the issue is that clang instantiates the assembly in all cases, producing the warning, *then* optimizes away the unreachable cases. If you ask clang to build the following: ---- #define __put_user(val, ptr) \ do { \ __typeof__(*(ptr)) __pu_val = (val); \ switch (sizeof(*(ptr))) { \ case 1: \ asm volatile ("strb %w1, %0" \ : "+Q" (*(ptr)) : "r" (__pu_val)); \ break; \ case 2: \ asm volatile ("strh %1, %0" \ : "+Q" (*(ptr)) : "r" (__pu_val)); \ break; \ case 4: \ asm volatile ("str %1, %0" \ : "+Q" (*(ptr)) : "r" (__pu_val)); \ break; \ case 8: \ asm volatile ("str %1, %0" \ : "+Q" (*(ptr)) : "r" (__pu_val)); \ break; \ } \ } while (0) void put_char(char in, char *ptr) { __put_user(in, ptr); } ---- It complains for all of the unmatched cases: ---- size-switch.c:26:2: warning: value size does not match register size specified by the constraint and modifier [-Wasm-operand-widths] __put_user(in, ptr); ^ size-switch.c:11:28: note: expanded from macro '__put_user' : "+Q" (*(ptr)) : "r" (__pu_val)); \ ^ size-switch.c:26:2: note: use constraint modifier "w" size-switch.c:10:23: note: expanded from macro '__put_user' asm volatile ("strh %1, %0" \ ^ size-switch.c:26:2: warning: value size does not match register size specified by the constraint and modifier [-Wasm-operand-widths] __put_user(in, ptr); ^ size-switch.c:15:28: note: expanded from macro '__put_user' : "+Q" (*(ptr)) : "r" (__pu_val)); \ ^ size-switch.c:26:2: note: use constraint modifier "w" size-switch.c:14:22: note: expanded from macro '__put_user' asm volatile ("str %1, %0" \ ^ size-switch.c:26:2: warning: value size does not match register size specified by the constraint and modifier [-Wasm-operand-widths] __put_user(in, ptr); ^ size-switch.c:19:28: note: expanded from macro '__put_user' : "+Q" (*(ptr)) : "r" (__pu_val)); \ ^ size-switch.c:26:2: note: use constraint modifier "w" size-switch.c:18:22: note: expanded from macro '__put_user' asm volatile ("str %1, %0" \ ^ 3 warnings generated. ---- AFAICT, in all other cases where we switch(sizeof(...)), we (will) use an explicit cast on the parameter, which placates clang. I think the best option is to get rid of __pu_val, and have an explicit cast of x in each case of the switch statement. I'll add that to my asm fixups series, with your Reported-by. Thanks, Mark.
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