Messages in this thread | | | Subject | Re: [PATCH] coresight: etm4x: work around clang-12+ build failure | From | Suzuki K Poulose <> | Date | Thu, 25 Feb 2021 17:20:57 +0000 |
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On 2/25/21 9:42 AM, Arnd Bergmann wrote: > From: Arnd Bergmann <arnd@arndb.de> > > clang-12 fails to build the etm4x driver with -fsanitize=array-bounds: > > <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" \ > ^ > > It appears that the __builin_constant_p() check in > read_etm4x_sysreg_offset() falsely returns 'true' here because clang > decides finds that an out-of-bounds access to config->cntr_val[] cannot
s/decides finds/decides/ ?
> happen, and then it unrolls the loop with constant register numbers. Then > when actually emitting the output, it fails to figure out the value again. > > While this is incorrect behavior in clang, it is easy to work around > by avoiding the out-of-bounds array access. Do this by limiting the > loop counter to the actual dimension of the array. > > Link: https://github.com/ClangBuiltLinux/linux/issues/1310 > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > --- > drivers/hwtracing/coresight/coresight-etm4x-core.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c > index 15016f757828..4cccf874a602 100644 > --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c > +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c > @@ -691,13 +691,13 @@ static void etm4_disable_hw(void *info) > "timeout while waiting for PM stable Trace Status\n"); > > /* read the status of the single shot comparators */ > - for (i = 0; i < drvdata->nr_ss_cmp; i++) { > + for (i = 0; i < min_t(u32, drvdata->nr_ss_cmp, ETM_MAX_SS_CMP); i++) { > config->ss_status[i] = > etm4x_relaxed_read32(csa, TRCSSCSRn(i)); > } >
There are more places where we do this. So I believe you need the similar change elsewhere too in the driver. So, that becomes cumbersome for circumventing the compiler issue.
Suzuki
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