On Thu, May 14, 2020 at 01:21:42PM +0200, Peter Zijlstra wrote: > On Wed, May 13, 2020 at 03:58:30PM +0200, Marco Elver wrote: > > On Wed, 13 May 2020 at 15:24, Peter Zijlstra <pet...@infradead.org> wrote: > > > > > > On Wed, May 13, 2020 at 03:15:55PM +0200, Marco Elver wrote: > > > > So far so good, except: both __no_sanitize_or_inline and > > > > __no_kcsan_or_inline *do* avoid KCSAN instrumenting plain accesses, it > > > > just doesn't avoid explicit kcsan_check calls, like those in > > > > READ/WRITE_ONCE if KCSAN is enabled for the compilation unit. That's > > > > just because macros won't be redefined just for __no_sanitize > > > > functions. Similarly, READ_ONCE_NOCHECK does work as expected, and its > > > > access is unchecked. > > > > > > > > This will have the expected result: > > > > __no_sanitize_or_inline void foo(void) { x++; } // no data races > > > > reported > > > > > > > > This will not work as expected: > > > > __no_sanitize_or_inline void foo(void) { READ_ONCE(x); } // data > > > > races are reported > > > > > > > > All this could be fixed if GCC devs would finally take my patch to > > > > make -fsanitize=thread distinguish volatile [1], but then we have to > > > > wait ~years for the new compilers to reach us. So please don't hold > > > > your breath for this one any time soon. > > > > [1] https://gcc.gnu.org/pipermail/gcc-patches/2020-April/544452.html > > > > > > Right, but that does not address the much larger issue of the attribute > > > vs inline tranwreck :/ > > > > Could you check if Clang is equally broken for you? I think GCC and > > Clang have differing behaviour on this. No idea what it takes to fix > > GCC though. > > So I have some good and some maybe not so good news. > > Given the patch below (on top of tglx's entry-v5-the-rest tag); I did > find that I could actually build alternative.o for gcc-{8,9,10} and > indeed clang-10. Any earlier gcc (I tried, 5,6,7) does not build: > > ../arch/x86/include/asm/ptrace.h:126:28: error: inlining failed in call to > always_inline ‘user_mode’: function attribute mismatch > > I dumped the poke_int3_handler output using objdump, find the attached > files. > > It looks like clang-10 doesn't want to turn UBSAN off :/ The GCC files > look OK, no funny calls in those. > > (the config has KASAN/UBSAN on, it looks like KCSAN and KASAN are > mutually exclusive)
I just swapped them and rebuild with gcc-10 and that still looks ok. 0000 0000000000000000 <poke_int3_handler>: 0000 0: f6 87 88 00 00 00 03 testb $0x3,0x88(%rdi) 0007 7: 75 4d jne 56 <poke_int3_handler+0x56> 0009 9: 48 8b 15 00 00 00 00 mov 0x0(%rip),%rdx # 10 <poke_int3_handler+0x10> 000c c: R_X86_64_PC32 .bss+0x101c 0010 10: 48 85 d2 test %rdx,%rdx 0013 13: 74 41 je 56 <poke_int3_handler+0x56> 0015 15: 8b 42 0c mov 0xc(%rdx),%eax 0018 18: 48 8d 4a 0c lea 0xc(%rdx),%rcx 001c 1c: 85 c0 test %eax,%eax 001e 1e: 74 36 je 56 <poke_int3_handler+0x56> 0020 20: 8d 70 01 lea 0x1(%rax),%esi 0023 23: f0 0f b1 31 lock cmpxchg %esi,(%rcx) 0027 27: 75 f3 jne 1c <poke_int3_handler+0x1c> 0029 29: 4c 8b 8f 80 00 00 00 mov 0x80(%rdi),%r9 0030 30: 48 63 42 08 movslq 0x8(%rdx),%rax 0034 34: 48 8b 32 mov (%rdx),%rsi 0037 37: 49 8d 49 ff lea -0x1(%r9),%rcx 003b 3b: 83 f8 01 cmp $0x1,%eax 003e 3e: 7f 19 jg 59 <poke_int3_handler+0x59> 0040 40: 4c 63 06 movslq (%rsi),%r8 0043 43: 31 c0 xor %eax,%eax 0045 45: 49 81 c0 00 00 00 00 add $0x0,%r8 0048 48: R_X86_64_32S _stext 004c 4c: 4c 39 c1 cmp %r8,%rcx 004f 4f: 74 39 je 8a <poke_int3_handler+0x8a> 0051 51: f0 ff 4a 0c lock decl 0xc(%rdx) 0055 55: c3 retq 0056 56: 31 c0 xor %eax,%eax 0058 58: c3 retq 0059 59: 49 89 f3 mov %rsi,%r11 005c 5c: 49 89 c2 mov %rax,%r10 005f 5f: 49 d1 ea shr %r10 0062 62: 4c 89 d6 mov %r10,%rsi 0065 65: 48 c1 e6 04 shl $0x4,%rsi 0069 69: 4c 01 de add %r11,%rsi 006c 6c: 4c 63 06 movslq (%rsi),%r8 006f 6f: 49 81 c0 00 00 00 00 add $0x0,%r8 0072 72: R_X86_64_32S _stext 0076 76: 4c 39 c1 cmp %r8,%rcx 0079 79: 0f 82 a2 00 00 00 jb 121 <poke_int3_handler+0x121> 007f 7f: 0f 87 83 00 00 00 ja 108 <poke_int3_handler+0x108> 0085 85: 48 85 f6 test %rsi,%rsi 0088 88: 74 45 je cf <poke_int3_handler+0xcf> 008a 8a: 0f b6 46 08 movzbl 0x8(%rsi),%eax 008e 8e: 44 8d 40 34 lea 0x34(%rax),%r8d 0092 92: 41 80 f8 1f cmp $0x1f,%r8b 0096 96: 76 02 jbe 9a <poke_int3_handler+0x9a> 0098 98: 0f 0b ud2 009a 9a: 45 0f b6 c0 movzbl %r8b,%r8d 009e 9e: 4d 0f be 80 00 00 00 movsbq 0x0(%r8),%r8 00a5 a5: 00 00a2 a2: R_X86_64_32S .rodata 00a6 a6: 4c 01 c1 add %r8,%rcx 00a9 a9: 3c e8 cmp $0xe8,%al 00ab ab: 74 29 je d6 <poke_int3_handler+0xd6> 00ad ad: 76 1c jbe cb <poke_int3_handler+0xcb> 00af af: 83 e0 fd and $0xfffffffd,%eax 00b2 b2: 3c e9 cmp $0xe9,%al 00b4 b4: 75 e2 jne 98 <poke_int3_handler+0x98> 00b6 b6: 48 63 46 04 movslq 0x4(%rsi),%rax 00ba ba: 48 01 c1 add %rax,%rcx 00bd bd: b8 01 00 00 00 mov $0x1,%eax 00c2 c2: 48 89 8f 80 00 00 00 mov %rcx,0x80(%rdi) 00c9 c9: eb 86 jmp 51 <poke_int3_handler+0x51> 00cb cb: 3c cc cmp $0xcc,%al 00cd cd: 75 c9 jne 98 <poke_int3_handler+0x98> 00cf cf: 31 c0 xor %eax,%eax 00d1 d1: e9 7b ff ff ff jmpq 51 <poke_int3_handler+0x51> 00d6 d6: 48 63 46 04 movslq 0x4(%rsi),%rax 00da da: 49 83 c1 04 add $0x4,%r9 00de de: 48 01 c1 add %rax,%rcx 00e1 e1: 48 8b 87 98 00 00 00 mov 0x98(%rdi),%rax 00e8 e8: 48 8d 70 f8 lea -0x8(%rax),%rsi 00ec ec: 48 89 b7 98 00 00 00 mov %rsi,0x98(%rdi) 00f3 f3: 4c 89 48 f8 mov %r9,-0x8(%rax) 00f7 f7: b8 01 00 00 00 mov $0x1,%eax 00fc fc: 48 89 8f 80 00 00 00 mov %rcx,0x80(%rdi) 0103 103: e9 49 ff ff ff jmpq 51 <poke_int3_handler+0x51> 0108 108: 48 83 e8 01 sub $0x1,%rax 010c 10c: 4c 8d 5e 10 lea 0x10(%rsi),%r11 0110 110: 48 d1 e8 shr %rax 0113 113: 48 85 c0 test %rax,%rax 0116 116: 0f 85 40 ff ff ff jne 5c <poke_int3_handler+0x5c> 011c 11c: e9 30 ff ff ff jmpq 51 <poke_int3_handler+0x51> 0121 121: 4c 89 d0 mov %r10,%rax 0124 124: eb ed jmp 113 <poke_int3_handler+0x113>