Add CWD handling to standalone WASI mode, and some related syscalls #24247
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This PR builds on top of #24246 and adds "proper" CWD handling in standalone WASI mode. It takes more code from PR #18285 (modified were needed).
Unlike wasi-libc, all of
chdir,fchdirandgetcwdare properly supported. This is done by maintaining a global directory fd inO_SEARCHmode and modifying the path resolution function__paths_resolve_path()frompaths.{h,c}accordingly.getcwdis implemented by walking from the current CWD fd "up" until a root, i.e. a preopened fd is reached, and comparing dirent inodes along the way.To support this, the following syscalls are implemented:
F_GETFD,F_SETFD,F_GETFLoffcntlfstatchdirfchdirgetcwdgetdents64(note that this now accesses thetellmember of theDIR*with someoffsetofhackery in order to find out the current offset inside the directory)The following tests work now in standalone WASM mode:
test_readdir: wastime and toywasm worktest_unistd_curdir: just toywasm works -- on wasmtime,openat(AT_FDCWD, "..")always seems to fail with a permission error, so the implementation strategy ofgetcwddoes not work right now. Wasmer can do this, but fails because of a symlink issue.test_unistd_cwd: just toywasm worksI had do to some minor adjustments to the tests.