| // Package psx provides support for system calls that are run |
| // simultaneously on all threads under Linux. |
| // |
| // This property can be used to work around a historical lack of |
| // native Go support for such a feature. Something that is the subject |
| // of: |
| // |
| // https://github.com/golang/go/issues/1435 |
| // |
| // The package works differently depending on whether or not |
| // CGO_ENABLED is 0 or 1. |
| // |
| // In the former case, psx is a low overhead wrapper for the two |
| // native go calls: syscall.AllThreadsSyscall() and |
| // syscall.AllThreadsSyscall6() introduced in go1.16. We provide this |
| // wrapping to minimize client source code changes when compiling with |
| // or without CGo enabled. |
| // |
| // In the latter case, and toolchains prior to go1.16, it works via |
| // CGo wrappers for system call functions that call the C [lib]psx |
| // functions of these names. This ensures that the system calls |
| // execute simultaneously on all the pthreads of the Go (and CGo) |
| // combined runtime. |
| // |
| // With CGo, the psx support works in the following way: the pthread |
| // that is first asked to execute the syscall does so, and determines |
| // if it succeeds or fails. If it fails, it returns immediately |
| // without attempting the syscall on other pthreads. If the initial |
| // attempt succeeds, however, then the runtime is stopped in order for |
| // the same system call to be performed on all the remaining pthreads |
| // of the runtime. Once all pthreads have completed the syscall, the |
| // return codes are those obtained by the first pthread's invocation |
| // of the syscall. |
| // |
| // Note, there is no need to use this variant of syscall where the |
| // syscalls only read state from the kernel. However, since Go's |
| // runtime freely migrates code execution between pthreads, support of |
| // this type is required for any successful attempt to fully drop or |
| // modify the privilege of a running Go program under Linux. |
| // |
| // More info on how Linux privilege works and examples of using this |
| // package can be found here: |
| // |
| // https://sites.google.com/site/fullycapable |
| // |
| // WARNING: For older go toolchains (prior to go1.15), correct |
| // compilation of this package may require an extra workaround step: |
| // |
| // The workaround is to build with the following CGO_LDFLAGS_ALLOW in |
| // effect (here the syntax is that of bash for defining an environment |
| // variable): |
| // |
| // export CGO_LDFLAGS_ALLOW="-Wl,-?-wrap[=,][^-.@][^,]*" |
| // |
| // |
| // Copyright (c) 2019,20 Andrew G. Morgan <morgan@kernel.org> |
| // |
| // The psx package is licensed with a (you choose) BSD 3-clause or |
| // GPL2. See LICENSE file for details. |
| package psx // import "kernel.org/pub/linux/libs/security/libcap/psx" |
