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