Re: [PATCH v5 00/18] Rework READ_ONCE() to improve codegen

From: Peter Zijlstra
Date: Thu May 14 2020 - 07:35:57 EST

On Thu, May 14, 2020 at 01:21:42PM +0200, Peter Zijlstra wrote:
> 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.


And, for completeness, here's the vomit from gcc-10 without the patch
for a KASAN+UBSAN build:


0000 0000000000000000 <poke_int3_handler>:
0000 0: 41 57 push %r15
0002 2: 41 56 push %r14
0004 4: 41 55 push %r13
0006 6: 41 54 push %r12
0008 8: 55 push %rbp
0009 9: 53 push %rbx
000a a: 48 89 fb mov %rdi,%rbx
000d d: 48 81 c7 88 00 00 00 add $0x88,%rdi
0014 14: 48 83 ec 10 sub $0x10,%rsp
0018 18: e8 00 00 00 00 callq 1d <poke_int3_handler+0x1d>
0019 19: R_X86_64_PLT32 __asan_load8_noabort-0x4
001d 1d: f6 83 88 00 00 00 03 testb $0x3,0x88(%rbx)
0024 24: 0f 85 99 00 00 00 jne c3 <poke_int3_handler+0xc3>
002a 2a: 48 8b 2d 00 00 00 00 mov 0x0(%rip),%rbp # 31 <poke_int3_handler+0x31>
002d 2d: R_X86_64_PC32 .bss+0x105c
0031 31: 48 85 ed test %rbp,%rbp
0034 34: 0f 84 89 00 00 00 je c3 <poke_int3_handler+0xc3>
003a 3a: 4c 8d 65 0c lea 0xc(%rbp),%r12
003e 3e: 4c 89 e7 mov %r12,%rdi
0041 41: e8 00 00 00 00 callq 46 <poke_int3_handler+0x46>
0042 42: R_X86_64_PLT32 __asan_load4_noabort-0x4
0046 46: 8b 45 0c mov 0xc(%rbp),%eax
0049 49: 85 c0 test %eax,%eax
004b 4b: 74 76 je c3 <poke_int3_handler+0xc3>
004d 4d: 8d 50 01 lea 0x1(%rax),%edx
0050 50: f0 41 0f b1 14 24 lock cmpxchg %edx,(%r12)
0056 56: 75 f1 jne 49 <poke_int3_handler+0x49>
0058 58: 48 8d bb 80 00 00 00 lea 0x80(%rbx),%rdi
005f 5f: e8 00 00 00 00 callq 64 <poke_int3_handler+0x64>
0060 60: R_X86_64_PLT32 __asan_load8_noabort-0x4
0064 64: 48 8b 83 80 00 00 00 mov 0x80(%rbx),%rax
006b 6b: 48 8d 7d 08 lea 0x8(%rbp),%rdi
006f 6f: 48 89 04 24 mov %rax,(%rsp)
0073 73: 4c 8d 60 ff lea -0x1(%rax),%r12
0077 77: e8 00 00 00 00 callq 7c <poke_int3_handler+0x7c>
0078 78: R_X86_64_PLT32 __asan_load4_noabort-0x4
007c 7c: 4c 63 7d 08 movslq 0x8(%rbp),%r15
0080 80: 48 89 ef mov %rbp,%rdi
0083 83: e8 00 00 00 00 callq 88 <poke_int3_handler+0x88>
0084 84: R_X86_64_PLT32 __asan_load8_noabort-0x4
0088 88: 4c 8b 6d 00 mov 0x0(%rbp),%r13
008c 8c: 41 83 ff 01 cmp $0x1,%r15d
0090 90: 7f 36 jg c8 <poke_int3_handler+0xc8>
0092 92: 4c 89 ef mov %r13,%rdi
0095 95: e8 00 00 00 00 callq 9a <poke_int3_handler+0x9a>
0096 96: R_X86_64_PLT32 __asan_load4_noabort-0x4
009a 9a: 49 63 55 00 movslq 0x0(%r13),%rdx
009e 9e: 45 31 c0 xor %r8d,%r8d
00a1 a1: 48 81 c2 00 00 00 00 add $0x0,%rdx
00a4 a4: R_X86_64_32S _stext
00a8 a8: 49 39 d4 cmp %rdx,%r12
00ab ab: 74 5d je 10a <poke_int3_handler+0x10a>
00ad ad: f0 ff 4d 0c lock decl 0xc(%rbp)
00b1 b1: 48 83 c4 10 add $0x10,%rsp
00b5 b5: 44 89 c0 mov %r8d,%eax
00b8 b8: 5b pop %rbx
00b9 b9: 5d pop %rbp
00ba ba: 41 5c pop %r12
00bc bc: 41 5d pop %r13
00be be: 41 5e pop %r14
00c0 c0: 41 5f pop %r15
00c2 c2: c3 retq
00c3 c3: 45 31 c0 xor %r8d,%r8d
00c6 c6: eb e9 jmp b1 <poke_int3_handler+0xb1>
00c8 c8: 4c 89 6c 24 08 mov %r13,0x8(%rsp)
00cd cd: 4d 89 fe mov %r15,%r14
00d0 d0: 48 8b 74 24 08 mov 0x8(%rsp),%rsi
00d5 d5: 49 d1 ee shr %r14
00d8 d8: 4c 89 f0 mov %r14,%rax
00db db: 48 c1 e0 04 shl $0x4,%rax
00df df: 4c 8d 2c 06 lea (%rsi,%rax,1),%r13
00e3 e3: 4c 89 ef mov %r13,%rdi
00e6 e6: e8 00 00 00 00 callq eb <poke_int3_handler+0xeb>
00e7 e7: R_X86_64_PLT32 __asan_load4_noabort-0x4
00eb eb: 49 63 4d 00 movslq 0x0(%r13),%rcx
00ef ef: 48 81 c1 00 00 00 00 add $0x0,%rcx
00f2 f2: R_X86_64_32S _stext
00f6 f6: 49 39 cc cmp %rcx,%r12
00f9 f9: 0f 82 fd 00 00 00 jb 1fc <poke_int3_handler+0x1fc>
00ff ff: 0f 87 d9 00 00 00 ja 1de <poke_int3_handler+0x1de>
0105 105: 4d 85 ed test %r13,%r13
0108 108: 74 7b je 185 <poke_int3_handler+0x185>
010a 10a: 49 8d 7d 08 lea 0x8(%r13),%rdi
010e 10e: e8 00 00 00 00 callq 113 <poke_int3_handler+0x113>
010f 10f: R_X86_64_PLT32 __asan_load1_noabort-0x4
0113 113: 45 0f b6 75 08 movzbl 0x8(%r13),%r14d
0118 118: 45 8d 7e 34 lea 0x34(%r14),%r15d
011c 11c: 41 80 ff 1f cmp $0x1f,%r15b
0120 120: 76 0e jbe 130 <poke_int3_handler+0x130>
0122 122: 0f 0b ud2
0124 124: 48 c7 c7 00 00 00 00 mov $0x0,%rdi
0127 127: R_X86_64_32S .data+0xc0
012b 12b: e8 00 00 00 00 callq 130 <poke_int3_handler+0x130>
012c 12c: R_X86_64_PLT32 __ubsan_handle_builtin_unreachable-0x4
0130 130: 45 0f b6 ff movzbl %r15b,%r15d
0134 134: 49 8d bf 00 00 00 00 lea 0x0(%r15),%rdi
0137 137: R_X86_64_32S .rodata+0x620
013b 13b: e8 00 00 00 00 callq 140 <poke_int3_handler+0x140>
013c 13c: R_X86_64_PLT32 __asan_load1_noabort-0x4
0140 140: 49 0f be 97 00 00 00 movsbq 0x0(%r15),%rdx
0147 147: 00
0144 144: R_X86_64_32S .rodata+0x620
0148 148: 49 01 d4 add %rdx,%r12
014b 14b: 41 80 fe e8 cmp $0xe8,%r14b
014f 14f: 74 3c je 18d <poke_int3_handler+0x18d>
0151 151: 76 2c jbe 17f <poke_int3_handler+0x17f>
0153 153: 41 83 e6 fd and $0xfffffffd,%r14d
0157 157: 41 80 fe e9 cmp $0xe9,%r14b
015b 15b: 75 c5 jne 122 <poke_int3_handler+0x122>
015d 15d: 49 8d 7d 04 lea 0x4(%r13),%rdi
0161 161: e8 00 00 00 00 callq 166 <poke_int3_handler+0x166>
0162 162: R_X86_64_PLT32 __asan_load4_noabort-0x4
0166 166: 49 63 45 04 movslq 0x4(%r13),%rax
016a 16a: 41 b8 01 00 00 00 mov $0x1,%r8d
0170 170: 49 01 c4 add %rax,%r12
0173 173: 4c 89 a3 80 00 00 00 mov %r12,0x80(%rbx)
017a 17a: e9 2e ff ff ff jmpq ad <poke_int3_handler+0xad>
017f 17f: 41 80 fe cc cmp $0xcc,%r14b
0183 183: 75 9d jne 122 <poke_int3_handler+0x122>
0185 185: 45 31 c0 xor %r8d,%r8d
0188 188: e9 20 ff ff ff jmpq ad <poke_int3_handler+0xad>
018d 18d: 49 8d 7d 04 lea 0x4(%r13),%rdi
0191 191: e8 00 00 00 00 callq 196 <poke_int3_handler+0x196>
0192 192: R_X86_64_PLT32 __asan_load4_noabort-0x4
0196 196: 49 63 45 04 movslq 0x4(%r13),%rax
019a 19a: 48 8d bb 98 00 00 00 lea 0x98(%rbx),%rdi
01a1 1a1: 49 01 c4 add %rax,%r12
01a4 1a4: e8 00 00 00 00 callq 1a9 <poke_int3_handler+0x1a9>
01a5 1a5: R_X86_64_PLT32 __asan_load8_noabort-0x4
01a9 1a9: 4c 8b b3 98 00 00 00 mov 0x98(%rbx),%r14
01b0 1b0: 49 8d 7e f8 lea -0x8(%r14),%rdi
01b4 1b4: 48 89 bb 98 00 00 00 mov %rdi,0x98(%rbx)
01bb 1bb: e8 00 00 00 00 callq 1c0 <poke_int3_handler+0x1c0>
01bc 1bc: R_X86_64_PLT32 __asan_store8_noabort-0x4
01c0 1c0: 4c 8b 2c 24 mov (%rsp),%r13
01c4 1c4: 41 b8 01 00 00 00 mov $0x1,%r8d
01ca 1ca: 49 83 c5 04 add $0x4,%r13
01ce 1ce: 4d 89 6e f8 mov %r13,-0x8(%r14)
01d2 1d2: 4c 89 a3 80 00 00 00 mov %r12,0x80(%rbx)
01d9 1d9: e9 cf fe ff ff jmpq ad <poke_int3_handler+0xad>
01de 1de: 49 8d 45 10 lea 0x10(%r13),%rax
01e2 1e2: 4d 8d 77 ff lea -0x1(%r15),%r14
01e6 1e6: 48 89 44 24 08 mov %rax,0x8(%rsp)
01eb 1eb: 49 d1 ee shr %r14
01ee 1ee: 4d 89 f7 mov %r14,%r15
01f1 1f1: 4d 85 ff test %r15,%r15
01f4 1f4: 0f 85 d3 fe ff ff jne cd <poke_int3_handler+0xcd>
01fa 1fa: eb 89 jmp 185 <poke_int3_handler+0x185>
01fc 1fc: 4d 89 f7 mov %r14,%r15
01ff 1ff: eb f0 jmp 1f1 <poke_int3_handler+0x1f1>