Fix docs about uninitialized bytes #5
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taiki-e
commented
Feb 26, 2022
| @@ -18,7 +18,7 @@ See [P1478R1][p1478r1] for more. | |||
| - If the alignment of the type being copied is the same as the pointer width, `atomic_load` is possible to produce an assembly roughly equivalent to the case of using volatile read + atomic fence on many platforms. (e.g., [aarch64](https://github.com/taiki-e/atomic-memcpy/blob/HEAD/tests/asm-test/asm/aarch64-unknown-linux-gnu/atomic_memcpy_load_align8), [riscv64](https://github.com/taiki-e/atomic-memcpy/blob/main/tests/asm-test/asm/riscv64gc-unknown-linux-gnu/atomic_memcpy_load_align8). See [`tests/asm-test/asm`][asm-test] directory for more). | |||
| - If the alignment of the type being copied is smaller than the pointer width, there will be some performance degradation. However, it is implemented in such a way that it does not cause extreme performance degradation at least on x86_64. (See [the implementation comments of `atomic_load`][implementation] for more.) It is possible that there is still room for improvement, especially on non-x86_64 platforms. | |||
| - Optimization for the case where the alignment of the type being copied is larger than the pointer width has not yet been fully investigated. It is possible that there is still room for improvement, especially on 32-bit platforms where `AtomicU64` is available. | |||
| - If the type being copied contains uninitialized bytes (e.g., padding), it is incompatible with `-Zmiri-check-number-validity`. This will probably not be resolved until something like `AtomicMaybeUninit` is supported. **Note:** Due to [Miri does not track uninitialized bytes on a per byte basis for partially initialized scalars][rust-lang/rust#69488], Miri may report this case as an access to an uninitialized byte, regardless of whether the uninitialized byte is actually accessed or not. | |||
| - If the type being copied contains uninitialized bytes (e.g., padding) [it is undefined behavior because the copy goes through integers][undefined-behavior]. This problem will probably not be resolved until something like `AtomicMaybeUninit` is supported. | |||
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I suppose the currently available (sound) workaround is to use inline assembly (#6), but that's hard to write/maintain, and not compatible with Miri (and sanitizers).
|
bors r+ |
|
Build succeeded: |
taiki-e
added a commit
that referenced
this pull request
Feb 2, 2025
```
AddressSanitizer:DEADLYSIGNAL
=================================================================
==3334==ERROR: AddressSanitizer: SEGV on unknown address 0x02000d2ef240 (pc 0x555e01b0afc7 bp 0x7ffc430de1b0 sp 0x7ffc430de100 T0)
==3334==The signal is caused by a READ memory access.
#0 0x555e01b0afc7 (/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-04c46d82177f025f+0x186fc7) (BuildId: 29923f56aa27c9d06e08f73052eb3efbd82fedaf)
#1 0x7fdf4de2a1c9 (/lib/x86_64-linux-gnu/libc.so.6+0x2a1c9) (BuildId: 6d64b17fbac799e68da7ebd9985ddf9b5cb375e6)
#2 0x7fdf4de2a28a (/lib/x86_64-linux-gnu/libc.so.6+0x2a28a) (BuildId: 6d64b17fbac799e68da7ebd9985ddf9b5cb375e6)
#3 0x555e01a56014 (/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-04c46d82177f025f+0xd2014) (BuildId: 29923f56aa27c9d06e08f73052eb3efbd82fedaf)
==3334==Register values:
rax = 0x000001ff8d2f7240 rbx = 0x00007ffc430de100 rcx = 0x0000000000000000 rdx = 0x000000008fff6fff
rdi = 0x00007fdf4be09010 rsi = 0x0000000000000000 rbp = 0x00007ffc430de1b0 rsp = 0x00007ffc430de100
r8 = 0x00000ffc697b9200 r9 = 0x0000000000000000 r10 = 0xafffff00000fff01 r11 = 0x4000000000000000
r12 = 0x00007ffc430de2d8 r13 = 0x0000000000000001 r14 = 0x00007fdf4be09000 r15 = 0x00000ffbe97c1200
AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-04c46d82177f025f+0x186fc7) (BuildId: 29923f56aa27c9d06e08f73052eb3efbd82fedaf)
==3334==ABORTING
error: test failed, to rerun pass `-p atomic-memcpy --lib`
Caused by:
process didn't exit successfully: `/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-04c46d82177f025f` (exit status: 1)
note: test exited abnormally; to see the full output pass --nocapture to the harness.
```
```
MemorySanitizer init done
MemorySanitizer:DEADLYSIGNAL
==3315==ERROR: MemorySanitizer: SEGV on unknown address 0x6fff3618a3d8 (pc 0x55a3c90d218a bp 0x000000000000 sp 0x7fff3618a1b0 T3315)
==3315==The signal is caused by a READ memory access.
#0 0x55a3c90d218a (/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-0e0b4cc066b47158+0x15f18a) (BuildId: eb746f488bb9238cde720cedbf7039f80464d20d)
#1 0x55a3c90d1b56 (/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-0e0b4cc066b47158+0x15eb56) (BuildId: eb746f488bb9238cde720cedbf7039f80464d20d)
#2 0x55a3c903f0ec (/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-0e0b4cc066b47158+0xcc0ec) (BuildId: eb746f488bb9238cde720cedbf7039f80464d20d)
#3 0x7fd98962a1c9 (/lib/x86_64-linux-gnu/libc.so.6+0x2a1c9) (BuildId: 6d64b17fbac799e68da7ebd9985ddf9b5cb375e6)
#4 0x7fd98962a28a (/lib/x86_64-linux-gnu/libc.so.6+0x2a28a) (BuildId: 6d64b17fbac799e68da7ebd9985ddf9b5cb375e6)
#5 0x55a3c8fcc214 (/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-0e0b4cc066b47158+0x59214) (BuildId: eb746f488bb9238cde720cedbf7039f80464d20d)
==3315==Register values:
rax = 0x0000000080000003 rbx = 0x0000500000000000 rcx = 0x00006fff3618a3d8 rdx = 0x0000100000000000
rdi = 0x00007fff3618a3d0 rsi = 0x00002fff3618a3d0 rbp = 0x0000000000000000 rsp = 0x00007fff3618a1b0
r8 = 0x00006fff3618a3d0 r9 = 0x0000000000000000 r10 = 0x000055a3c8f8f0bf r11 = 0x0000000000000206
r12 = 0x0000500000000000 r13 = 0x00002fff3618a3a0 r14 = 0x00007fff3618a3d0 r15 = 0xffffffffffffef60
MemorySanitizer can not provide additional info.
SUMMARY: MemorySanitizer: SEGV (/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-0e0b4cc066b47158+0x15f18a) (BuildId: eb746f488bb9238cde720cedbf7039f80464d20d)
==3315==ABORTING
error: test failed, to rerun pass `-p atomic-memcpy --lib`
Caused by:
process didn't exit successfully: `/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-0e0b4cc066b47158` (exit status: 1)
note: test exited abnormally; to see the full output pass --nocapture to the harness.
```
taiki-e
added a commit
that referenced
this pull request
Feb 2, 2025
```
AddressSanitizer:DEADLYSIGNAL
=================================================================
==3334==ERROR: AddressSanitizer: SEGV on unknown address 0x02000d2ef240 (pc 0x555e01b0afc7 bp 0x7ffc430de1b0 sp 0x7ffc430de100 T0)
==3334==The signal is caused by a READ memory access.
#0 0x555e01b0afc7 (/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-04c46d82177f025f+0x186fc7) (BuildId: 29923f56aa27c9d06e08f73052eb3efbd82fedaf)
#1 0x7fdf4de2a1c9 (/lib/x86_64-linux-gnu/libc.so.6+0x2a1c9) (BuildId: 6d64b17fbac799e68da7ebd9985ddf9b5cb375e6)
#2 0x7fdf4de2a28a (/lib/x86_64-linux-gnu/libc.so.6+0x2a28a) (BuildId: 6d64b17fbac799e68da7ebd9985ddf9b5cb375e6)
#3 0x555e01a56014 (/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-04c46d82177f025f+0xd2014) (BuildId: 29923f56aa27c9d06e08f73052eb3efbd82fedaf)
==3334==Register values:
rax = 0x000001ff8d2f7240 rbx = 0x00007ffc430de100 rcx = 0x0000000000000000 rdx = 0x000000008fff6fff
rdi = 0x00007fdf4be09010 rsi = 0x0000000000000000 rbp = 0x00007ffc430de1b0 rsp = 0x00007ffc430de100
r8 = 0x00000ffc697b9200 r9 = 0x0000000000000000 r10 = 0xafffff00000fff01 r11 = 0x4000000000000000
r12 = 0x00007ffc430de2d8 r13 = 0x0000000000000001 r14 = 0x00007fdf4be09000 r15 = 0x00000ffbe97c1200
AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-04c46d82177f025f+0x186fc7) (BuildId: 29923f56aa27c9d06e08f73052eb3efbd82fedaf)
==3334==ABORTING
error: test failed, to rerun pass `-p atomic-memcpy --lib`
Caused by:
process didn't exit successfully: `/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-04c46d82177f025f` (exit status: 1)
note: test exited abnormally; to see the full output pass --nocapture to the harness.
```
```
MemorySanitizer init done
MemorySanitizer:DEADLYSIGNAL
==3315==ERROR: MemorySanitizer: SEGV on unknown address 0x6fff3618a3d8 (pc 0x55a3c90d218a bp 0x000000000000 sp 0x7fff3618a1b0 T3315)
==3315==The signal is caused by a READ memory access.
#0 0x55a3c90d218a (/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-0e0b4cc066b47158+0x15f18a) (BuildId: eb746f488bb9238cde720cedbf7039f80464d20d)
#1 0x55a3c90d1b56 (/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-0e0b4cc066b47158+0x15eb56) (BuildId: eb746f488bb9238cde720cedbf7039f80464d20d)
#2 0x55a3c903f0ec (/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-0e0b4cc066b47158+0xcc0ec) (BuildId: eb746f488bb9238cde720cedbf7039f80464d20d)
#3 0x7fd98962a1c9 (/lib/x86_64-linux-gnu/libc.so.6+0x2a1c9) (BuildId: 6d64b17fbac799e68da7ebd9985ddf9b5cb375e6)
#4 0x7fd98962a28a (/lib/x86_64-linux-gnu/libc.so.6+0x2a28a) (BuildId: 6d64b17fbac799e68da7ebd9985ddf9b5cb375e6)
#5 0x55a3c8fcc214 (/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-0e0b4cc066b47158+0x59214) (BuildId: eb746f488bb9238cde720cedbf7039f80464d20d)
==3315==Register values:
rax = 0x0000000080000003 rbx = 0x0000500000000000 rcx = 0x00006fff3618a3d8 rdx = 0x0000100000000000
rdi = 0x00007fff3618a3d0 rsi = 0x00002fff3618a3d0 rbp = 0x0000000000000000 rsp = 0x00007fff3618a1b0
r8 = 0x00006fff3618a3d0 r9 = 0x0000000000000000 r10 = 0x000055a3c8f8f0bf r11 = 0x0000000000000206
r12 = 0x0000500000000000 r13 = 0x00002fff3618a3a0 r14 = 0x00007fff3618a3d0 r15 = 0xffffffffffffef60
MemorySanitizer can not provide additional info.
SUMMARY: MemorySanitizer: SEGV (/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-0e0b4cc066b47158+0x15f18a) (BuildId: eb746f488bb9238cde720cedbf7039f80464d20d)
==3315==ABORTING
error: test failed, to rerun pass `-p atomic-memcpy --lib`
Caused by:
process didn't exit successfully: `/home/runner/work/atomic-memcpy/atomic-memcpy/target/x86_64-unknown-linux-gnu/release/deps/atomic_memcpy-0e0b4cc066b47158` (exit status: 1)
note: test exited abnormally; to see the full output pass --nocapture to the harness.
```
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Based on the feedback from @RalfJung.