Messages in this thread | | | Subject | Re: [PATCH] [v2] coresight: etm4x: avoid build failure with unrolled loops | From | Suzuki K Poulose <> | Date | Thu, 29 Apr 2021 23:49:53 +0100 |
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On 29/04/2021 18:50, Arnd Bergmann wrote: > On Thu, Apr 29, 2021 at 7:37 PM Suzuki K Poulose <suzuki.poulose@arm.com> wrote: >> On 29/04/2021 15:57, Arnd Bergmann wrote: >>> From: Arnd Bergmann <arnd@arndb.de> >>> >>> clang-12 fails to build the etm4x driver with -fsanitize=array-bounds, >>> where it decides to unroll certain loops in a way that result in a >>> C variable getting put into an inline assembly >>> >>> <instantiation>:1:7: error: expected constant expression in '.inst' directive >>> .inst (0xd5200000|((((2) << 19) | ((1) << 16) | (((((((((((0x160 + (i * 4))))) >> 2))) >> 7) & 0x7)) << 12) | ((((((((((0x160 + (i * 4))))) >> 2))) & 0xf)) << 8) | (((((((((((0x160 + (i * 4))))) >> 2))) >> 4) & 0x7)) << 5)))|(.L__reg_num_x8)) >>> ^ >>> drivers/hwtracing/coresight/coresight-etm4x-core.c:702:4: note: while in macro instantiation >>> etm4x_relaxed_read32(csa, TRCCNTVRn(i)); >>> ^ >>> drivers/hwtracing/coresight/coresight-etm4x.h:403:4: note: expanded from macro 'etm4x_relaxed_read32' >>> read_etm4x_sysreg_offset((offset), false))) >>> ^ >>> drivers/hwtracing/coresight/coresight-etm4x.h:383:12: note: expanded from macro 'read_etm4x_sysreg_offset' >>> __val = read_etm4x_sysreg_const_offset((offset)); \ >>> ^ >>> drivers/hwtracing/coresight/coresight-etm4x.h:149:2: note: expanded from macro 'read_etm4x_sysreg_const_offset' >>> READ_ETM4x_REG(ETM4x_OFFSET_TO_REG(offset)) >>> ^ >>> drivers/hwtracing/coresight/coresight-etm4x.h:144:2: note: expanded from macro 'READ_ETM4x_REG' >>> read_sysreg_s(ETM4x_REG_NUM_TO_SYSREG((reg))) >>> ^ >>> arch/arm64/include/asm/sysreg.h:1108:15: note: expanded from macro 'read_sysreg_s' >>> asm volatile(__mrs_s("%0", r) : "=r" (__val)); \ >>> ^ >>> arch/arm64/include/asm/sysreg.h:1074:2: note: expanded from macro '__mrs_s' >>> " mrs_s " v ", " __stringify(r) "\n" \ >>> ^ >>> >>> This only happened in a few loops in which the array bounds sanitizer >>> added a special case for an array overflow that clang determined to be >>> possible, but any compiler is free to unroll any of the loops in the >>> same way that breaks the sysreg macros. >>> >>> Introduce helper functions that perform a sysreg access with a >>> non-constant register number and use them in each call that passes >>> a loop counter. >> >> You don't need to add this special helper. We have the exact >> infrastructure already. So these could simply be replaced with: >> >> csdev_access_xxx(csa, ...) >> >> see : >> >> include/linux/coresight.h > > Ah, nice! > > Do you mean replacing only the ones that use a nonconstant > offset, or all of them? I guess changing all would avoid some
Only the CLANG "nonconstant" please. Going through an indirect function call and large "switch..case" for every single register access is painful. Which is why I decided to add those ugly macros.
So, please leave the rest as they are.
Suzuki
> really ugly magic macros, but the indirect function call and the > switch() adds a few cycles of overhead every time and the code > looks like it is micro-optimized for fast register access here. > > Arnd >
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