Messages in this thread | | | Date | Mon, 27 Jun 2022 22:44:34 +0100 | Subject | Re: [PATCH v5] coresight: etm4x: avoid build failure with unrolled loops | From | Suzuki K Poulose <> |
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Hi Nick,
Thanks for the rework.
On 23/06/2022 18:41, Nick Desaulniers wrote: > 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 which 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 > construct 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_relaxed_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. > > For such cases where the induction variable is used in an expression, > perform the following function call replacements: > * etm4x_relaxed_write32 -> csdev_access_relaxed_write32 > * etm4x_relaxed_write64 -> csdev_access_relaxed_write64 > * etm4x_relaxed_read32 -> csdev_access_relaxed_read32 > * etm4x_read32 -> csdev_access_read32 > * etm4x_read64 -> csdev_access_read64 > > 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 > Reported-by: Arnd Bergmann <arnd@kernel.org> > Suggested-by: Arnd Bergmann <arnd@kernel.org> > Suggested-by: Tao Zhang <quic_taozha@quicinc.com> > Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
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