| commit | 1eaa289472aaddbeabcde10f89cffb161c2dca55 | [log] [tgz] |
|---|---|---|
| author | Pavel Labath <pavel@labath.sk> | Tue May 06 15:04:30 2025 +0200 |
| committer | GitHub <noreply@github.com> | Tue May 06 15:04:30 2025 +0200 |
| tree | a0e80aae97765995840beb61a170ab3cc44ef547 | |
| parent | d90cac964130004d449b94f6020264c14e1cb999 [diff] |
[lldb/Host] Enable inheriting "non-inheritable" FDs (#126935) Currently we're creating inheritable (`~FD_CLOEXEC`) file descriptors in the (few) cases where we need to pass an FD to a subprocess. The problem with these is that, in a multithreaded application such as lldb, there's essentially no way to prevent them from being leaked into processes other than the intended one. A safer (though still not completely safe) approach is to mark the descriptors as FD_CLOEXEC and only clear this flag in the subprocess. We currently have something that almost does that, which is the ability to add a `DuplicateFileAction` to our `ProcessLaunchInfo` struct (the duplicated file descriptor will be created with the flag cleared). The problem with *that* is that this approach is completely incompatible with Windows. Windows equivalents of file descriptors are `HANDLE`s, but these do not have user controlled values -- applications are expected to work with whatever HANDLE values are assigned by the OS. In unix terms, there is no equivalent to the `dup2` syscall (only `dup`). To find a way out of this conundrum, and create a miniscule API surface that works uniformly across platforms, this PR proposes to extend the `DuplicateFileAction` API to support duplicating a file descriptor onto itself. Currently, this operation does nothing (it leaves the FD_CLOEXEC flag set), because that's how `dup2(fd, fd)` behaves, but I think it's not completely unreasonable to say that this operation should clear the FD_CLOEXEC flag, just like it would do if one was using different fd values. This would enable us to pass a windows HANDLE as itself through the ProcessLaunchInfo API. This PR implements the unix portion of this idea. Macos and non-macos launchers are updated to clear FD_CLOEXEC flag when duplicating a file descriptor onto itself, and I've created a test which enables passing a FD_CLOEXEC file descritor to the subprocess. For the windows portion, please see the follow-up PR.
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