lib/posix-process: Add vfork & execve #1386
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Add an architecture specific getter for the stack pointer of a `struct __regs`. Signed-off-by: Sergiu Moga <sergiu@unikraft.io> Signed-off-by: Michalis Pappas <michalis@unikraft.io> Co-authored-by: Michalis Pappas <michalis@unikraft.io>
libukbinfmt provides a minimal framework to register handlers of executable files. Typical examples include binary executables like ELF objects, or interpreted files like *nix scripts that use the sha-bang sequence to specify an interpreter. This commit only implements the functionality required to register and execute loaders within the kernel's scope. Additional functionality incl. application support via Linux's `binfmt_misc` API shall be added as a future extension. Checkpatch-Ignore: COMPLEX_MACRO Checkpatch-Ignore: MACRO_ARG_REUSE Signed-off-by: Michalis Pappas <michalis@unikraft.io>
Add definition of ARG_MAX to limits.h. POSIX defines ARG_MAX as the number of bytes available for the combined arguments and env vars of a new process. Whether that additionally includes NULL terminator, pointers, or alignment bytes is IMPLEMENTATION DEFINED. Signed-off-by: Michalis Pappas <michalis@unikraft.io>
Migrate the definitions of tid2pthread() and tid2pprocess() to the private process.h to make them available to the rest of the library. This requires to additionally migrate the definitions of struct posix_process() and struct posix_thread(). Signed-off-by: Michalis Pappas <michalis@unikraft.io>
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The state provides information on whether a posix_thread is running, blocked, or exited. Notice that posix_thread_state is only updated by operations at the posix_process / posix_thread level and may not always be in sync with the state of the underlying uk_thread. This specifically applies to the POSIX_THREAD_RUNNING state, which may not be accurate e.g. if the underlying uk_thread blocks at the scheduler due to a lock. On the other hand, the variants of POSIX_STATE_BLOCKED always reflect the state of a posix_thread, as it is certain that the underlying uk_thread will also be blocked from the scheduler. Given the above, a check against POSIX_STATE_RUNNING should only be used to check if the state of a posix-thread is not terminated or blocked. Signed-off-by: Michalis Pappas <michalis@unikraft.io>
Add a field to posix_thread to keep track of its parent. This is populated during the creation of a posix_thread, and it is used for deriving the parent's state in execve() / exit(). Signed-off-by: Michalis Pappas <michalis@unikraft.io>
Add implementation for execve(). For more info see execve(2). Requires a binfmt ELF loader. The default loader is provided by app-bincompat. Checkpatch-Ignore: AVOID_EXTERNS Signed-off-by: Michalis Pappas <michalis@unikraft.io>
vfork() sets the CLONE_VM and CLONE_VFORK flags. This triggers an error in the clone handlers of vfscore as CLONE_FS is not set. Update the handlers to additionally check against CLONE_VM, as that also implies that the parent and child share filesystem state. Signed-off-by: Michalis Pappas <michalis@unikraft.io>
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The vfork() syscall is equivalent to calling clone() with the flags parameter set to CLONE_VM | CLONE_VFORK | SIGCHLD. Update clone() to support CLONE_VFORK and CLONE_VM. Implement vfork() as a wrapper of clone(). For more info see vfork(2). Signed-off-by: Michalis Pappas <michalis@unikraft.io>
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I pushed an update where I shadow elements of |
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Prerequisite checklist
checkpatch.ukon your commit series before opening this PR;Base target
Additional configuration
execve()syscallvfork()syscallukbinfmtlibraryDescription of changes
This PR adds support for
vfork()/execve()to libposix-process. This provides the foundation for running multiprocess applications on Unikraft.vfork()creates a child process that shares the same memory with the calling thread, including the stack. Uponvfork()the parent is suspended until the child callsexecve()or_exit()to prevent the parent's state from being corrupted. Due to above, the only permissible actions taken by the child are:pid_tto store its return value.exec(2)family, or_exit(2).Any action besides the above results into undefined behavior.
For a more elaborate description on
vfork()see vfork(2).execve()implements the standard behavior described in execve(2). To provide flexibility on the supported binary formats the implementation relies onlibukbinfmt, which is also introducedin this series. Similarly to linux, this provides a minimal framework for registering loaders that handle different binary formats, introducing the ability of loading interpreted scripts. The implementation may be extended with support for linux'sbinfmt_miscfs, should such a use-case arise. The implementation of the ELFukbinfmtloader is introduced inapp-elfloader.GitHub-Depends-On: #1316
GitHub-Depends-On: #1322
GitHub-Depends-On: #1346
GitHub-Depends-On: unikraft/app-elfloader#79