support userfaultfd?
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- Dominant language
- C++
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Description
Chrome when running on chromeos uses the userfaultfd syscall and rr fails with
[FATAL /usr/local/google/home/fergal/github/rr-debugger/rr/src/record_syscall.cc:5846:rec_process_syscall_arch()]
(task 1715052 (rec:1715052) at time 16963)
-> Assertion `t->regs().syscall_result_signed() == -syscall_state.expect_errno' failed to hold. Expected ENOSYS for 'userfaultfd' but got result -22 (errno EINVAL); execution of syscall unsupported by rr
Relevant Chrome src is here.
Can we get rr to support this syscall? Thanks.
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First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start in src/record_syscall.cc around line 5846, where the userfaultfd syscall currently produces the ENOSYS expectation failure. Compare that handling with the ChromeOS userspace_swap.cc reference linked in the issue and use the reported Chrome-on-ChromeOS case as the reproduction. Done means rr can record this syscall without the assertion failure.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- cpp, linux
- Domain
- devtools, operating-systems
- Issue type
- Feature
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100