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Date: Tue, 14 Jun 2022 15:02:29 -0700
From: Nick Desaulniers <ndesaulniers@...gle.com>
To: Mathieu Poirier <mathieu.poirier@...aro.org>,
Suzuki K Poulose <suzuki.poulose@....com>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>,
Arnd Bergmann <arnd@...nel.org>,
Tao Zhang <quic_taozha@...cinc.com>,
Mike Leach <mike.leach@...aro.org>,
Leo Yan <leo.yan@...aro.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Nathan Chancellor <nathan@...nel.org>,
Tom Rix <trix@...hat.com>, coresight@...ts.linaro.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
llvm@...ts.linux.dev
Subject: [PATCH v4] coresight: etm4x: avoid build failure with unrolled loops
When the following configs are enabled:
* CORESIGHT
* CORESIGHT_SOURCE_ETM4X
* UBSAN
* UBSAN_TRAP
Clang fails assemble the kernel with the error:
<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" \
^
Consider the definitions of TRCSSCSRn and TRCCNTVRn:
drivers/hwtracing/coresight/coresight-etm4x.h:56
#define TRCCNTVRn(n) (0x160 + (n * 4))
drivers/hwtracing/coresight/coresight-etm4x.h:81
#define TRCSSCSRn(n) (0x2A0 + (n * 4))
Where the macro parameter is expanded to i; a loop induction variable
from etm4_disable_hw.
When any compiler can determine that loops may be unrolled, then the
__builtin_constant_p check in read_etm4x_sysreg_offset() defined in
drivers/hwtracing/coresight/coresight-etm4x.h may evaluate to true. This
can lead to the expression `(0x160 + (i * 4))` being passed to
read_etm4x_sysreg_const_offset. Via the trace above, this is passed
through READ_ETM4x_REG, read_sysreg_s, and finally to __mrs_s where it
is string-ified and used directly in inline asm.
Regardless of compiler or compiler options determine whether a loop can
or can't be unrolled, which determines whether __builtin_constant_p
evaluates to true when passed an expression using a loop induction
variable, it is NEVER safe to allow the preprocessor to construction
inline asm like:
asm volatile (".inst (0x160 + (i * 4))" : "=r"(__val));
^ expected constant expression
Replace unsafe uses of calls to etm4x_relaxed_read32 with
csdev_access_read32 when the parameter is an expression that would be
invalid inline asm so that it does not depend on the ability of the
compiler to optimize __builtin_constant_p of the expression to true.
Only when the second parameter of etm4x_relaxed_read32 expands to an
expression dependent on a loop induction variable do we need to fix
this.
This is not a bug in clang; it's a potentially unsafe use of the macro
arguments in read_etm4x_sysreg_offset dependent on __builtin_constant_p.
Link: https://github.com/ClangBuiltLinux/linux/issues/1310
Suggested-by: Arnd Bergmann <arnd@...nel.org>
Suggested-by: Tao Zhang <quic_taozha@...cinc.com>
Suggested-by: Suzuki K Poulose <suzuki.poulose@....com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
V1 (Arnd):
https://lore.kernel.org/lkml/20210225094324.3542511-1-arnd@kernel.org/
V2 (Arnd):
https://lore.kernel.org/lkml/20210429145752.3218324-1-arnd@kernel.org/
V3 (Tao):
https://lore.kernel.org/lkml/1632652550-26048-1-git-send-email-quic_taozha@quicinc.com/
drivers/hwtracing/coresight/coresight-etm4x-core.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index 87299e99dabb..7c6bd85e36d4 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -836,13 +836,13 @@ static void etm4_disable_hw(void *info)
/* read the status of the single shot comparators */
for (i = 0; i < drvdata->nr_ss_cmp; i++) {
config->ss_status[i] =
- etm4x_relaxed_read32(csa, TRCSSCSRn(i));
+ csdev_access_read32(csa, TRCSSCSRn(i));
}
/* read back the current counter values */
for (i = 0; i < drvdata->nr_cntr; i++) {
config->cntr_val[i] =
- etm4x_relaxed_read32(csa, TRCCNTVRn(i));
+ csdev_access_read32(csa, TRCCNTVRn(i));
}
coresight_disclaim_device_unlocked(csdev);
@@ -1177,7 +1177,7 @@ static void etm4_init_arch_data(void *info)
drvdata->nr_ss_cmp = FIELD_GET(TRCIDR4_NUMSSCC_MASK, etmidr4);
for (i = 0; i < drvdata->nr_ss_cmp; i++) {
drvdata->config.ss_status[i] =
- etm4x_relaxed_read32(csa, TRCSSCSRn(i));
+ csdev_access_read32(csa, TRCSSCSRn(i));
}
/* NUMCIDC, bits[27:24] number of Context ID comparators for tracing */
drvdata->numcidc = FIELD_GET(TRCIDR4_NUMCIDC_MASK, etmidr4);
--
2.36.1.476.g0c4daa206d-goog
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