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 18:37:38 +0100 |
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Hi Arnd
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
Cheers Suzuki
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