On Wed, 20 Nov 2019 at 17:18, Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote: > > On 11/20/19 1:34 AM, Stephen Rothwell wrote: > > Hi all, > > > > Changes since 20191119: > > > > on x86_64: > > kernel/kcsan/core.o: warning: objtool: kcsan_found_watchpoint()+0xa: call to kcsan_is_enabled() with UACCESS enabled > kernel/kcsan/core.o: warning: objtool: __tsan_read1()+0x13: call to find_watchpoint() with UACCESS enabled > kernel/kcsan/core.o: warning: objtool: __tsan_write1()+0x10: call to find_watchpoint() with UACCESS enabled > kernel/kcsan/core.o: warning: objtool: __tsan_read2()+0x13: call to find_watchpoint() with UACCESS enabled > kernel/kcsan/core.o: warning: objtool: __tsan_write2()+0x10: call to find_watchpoint() with UACCESS enabled > kernel/kcsan/core.o: warning: objtool: __tsan_read4()+0x13: call to find_watchpoint() with UACCESS enabled > kernel/kcsan/core.o: warning: objtool: __tsan_write4()+0x10: call to find_watchpoint() with UACCESS enabled > kernel/kcsan/core.o: warning: objtool: __tsan_read8()+0x13: call to find_watchpoint() with UACCESS enabled > kernel/kcsan/core.o: warning: objtool: __tsan_write8()+0x10: call to find_watchpoint() with UACCESS enabled > kernel/kcsan/core.o: warning: objtool: __tsan_read16()+0x13: call to find_watchpoint() with UACCESS enabled > kernel/kcsan/core.o: warning: objtool: __tsan_write16()+0x10: call to find_watchpoint() with UACCESS enabled > kernel/kcsan/core.o: warning: objtool: __tsan_read_range()+0x13: call to find_watchpoint() with UACCESS enabled > kernel/kcsan/core.o: warning: objtool: __tsan_write_range()+0x10: call to find_watchpoint() with UACCESS enabled > > kernel/trace/trace_branch.o: warning: objtool: ftrace_likely_update()+0x361: call to __stack_chk_fail() with UACCESS enabled > > > Full randconfig file is attached. Thanks. This is due to CONFIG_CC_OPTIMIZE_FOR_SIZE=y. It seems the compiler decides to not even inline small static inline functions. I tried to make this go away by adding __always_inline, but then we're also left with atomic64_try_cmpxchg which never gets inlined. The optimized build simply inlines the small static inline functions. We certainly do not want to add more functions to the objtool whitelist, especially those that are private to KCSAN. We could fix it by either: 1. Adding __always_inline to every function used by the KCSAN runtime outside user_access_save + also fix atomic64_try_cmpxchg (atomic-instrumented.h). 2. Just not compile KCSAN with -Os, i.e. have the Makefile strip -Os and replace it with -O2 for kcsan/core.c. #2 is the simpler option, and would probably make KCSAN more effective even with -Os. Although it might violate the assumption of whoever decided they want both CC_OPTIMIZE_FOR_SIZE and KCSAN. It might also mean that future compilers that have a new inlining algorithm will have the same problem. What do people think is better? Thanks, -- Marco > -- > ~Randy > Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
