Wasmtime GitHub notifications bot (Oct 08 2021 at 11:37): Wasmtime GitHub notifications bot (Oct 08 2021 at 11:37):akirilov-arm opened PR #3426 from membarrier to main:
This is the first part of a fix to issue #3310. Unfortunately, there are more calls than necessary to
rsix::process::membarrier(rsix::process::MembarrierCommand::RegisterPrivateExpeditedSyncCore)(it is sufficient to call it once per process), but bothcranelift_jit::JITModuleandwasmtime_jit::CodeMemoryare public interfaces, so my current approach is the best I have come up with that hides this AArch64 memory model detail from any crate users; I would appreciate any suggestions for improvements.
Wasmtime GitHub notifications bot (Oct 08 2021 at 11:44):bjorn3 submitted PR review.
Wasmtime GitHub notifications bot (Oct 08 2021 at 11:44):bjorn3 created PR review comment:
Please avoid rsix in cranelift-jit: https://github.com/bytecodealliance/wasmtime/pull/3395 I think
libc::syscall(libc::SYS_membarrier, 32u32)will work. 32 isMEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_COREon AArch64: https://github.com/sunfishcode/linux-raw-sys/blob/6d0a83985c28678821d2d67f3047c7fe2b90a6ae/src/v5_4/aarch64/general.rs#L3443
Wasmtime GitHub notifications bot (Oct 08 2021 at 11:48):bjorn3 created PR review comment:
Is this for the new libcall PLT entries generated above? I think this will need to be called every time a new PLT entry is generated like in
declare_function.
Wasmtime GitHub notifications bot (Oct 08 2021 at 11:48):bjorn3 submitted PR review.
Wasmtime GitHub notifications bot (Oct 08 2021 at 11:50):bjorn3 created PR review comment:
Also I think this will need to be called every time a new PLT entry is generated like in
declare_functionornew.
Wasmtime GitHub notifications bot (Oct 08 2021 at 11:50):bjorn3 submitted PR review.
Wasmtime GitHub notifications bot (Oct 14 2021 at 18:11):akirilov-arm submitted PR review.
Wasmtime GitHub notifications bot (Oct 14 2021 at 18:11):akirilov-arm created PR review comment:
This needs to be called when we are just about to start executing from the generated code, which is usually around the time the code memory's protection is changed from readable and writable to readable and executable. As far as I can tell, generating a new PLT entry involves just writing some data (i.e. instructions) into the instruction stream, but does not create new executable memory (via changing permissions), nor does it involve memory that is simultaneously readable, writable, and executable.
Wasmtime GitHub notifications bot (Oct 14 2021 at 18:50):bjorn3 submitted PR review.
Wasmtime GitHub notifications bot (Oct 14 2021 at 18:50):bjorn3 created PR review comment:
New PLT entries are handled the same way as adding new functions. Both first write the code to a writeable page and then use mprotect to make it executable.
Wasmtime GitHub notifications bot (Oct 14 2021 at 21:29):akirilov-arm submitted PR review.
Wasmtime GitHub notifications bot (Oct 14 2021 at 21:29):akirilov-arm created PR review comment:
Sure, but it looks like
new_plt_entry()just does an allocation and writes the code. The only place where we make the transition from readable and writable memory to readable and executable is insidefinalize_definitions()and there we handle both normal generated functions and PLT entries together - am I missing something?
Wasmtime GitHub notifications bot (Oct 15 2021 at 16:54):akirilov-arm updated PR #3426 from membarrier to main.
Wasmtime GitHub notifications bot (Oct 18 2021 at 15:17):alexcrichton submitted PR review.
Wasmtime GitHub notifications bot (Oct 22 2021 at 19:31):akirilov-arm updated PR #3426 from membarrier to main.
Wasmtime GitHub notifications bot (Oct 25 2021 at 12:25):akirilov-arm merged PR #3426.
Last updated: Dec 23 2024 at 12:05 UTC