add stubs for statvfs, chmod, etc.
#463
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Per WebAssembly/wasi-sdk#373, LLVM's libc++ no longer allows us to enable `<fstream>` and `<filesystem>` separately -- it's both or neither. Consequently, we either need to patch libc++ to not use `statvfs`, `chmod`, etc. or add stub functions for those features to `wasi-libc`. Since we're planning to eventually support those features with WASI Preview 2 and beyond, it makes sense to do the latter. Note that since libc++ uses `DT_SOCK`, I've added a definition for it -- even though WASI Preview 1 does not define it. No Preview 1 file will ever have that type, so code that handles that type will never be reached, but defining it allows us to avoid WASI-specific patches to libc++. Related to `DT_SOCK`, I had to change the `S_IFIFO` value so it does not conflict with `S_IFSOCK`, thereby avoiding ambiguity in `__wasilibc_iftodt`. Signed-off-by: Joel Dice <[email protected]>
yamt
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Jan 23, 2024
| || defined(_BSD_SOURCE) | ||
| #ifdef __wasilibc_unmodified_upstream /* WASI has no absolute paths */ | ||
| char *realpath (const char *__restrict, char *__restrict); | ||
| #endif |
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Yes -- realpath is one of the functions libcxx's <filesystem> relies on, although I just realized I neglected to add realpath.c to LIBC_TOP_HALF_MUSL_SOURCES in the Makefile, and I'm not sure if that implementation is what we want (vs. a stub), so I'll need to take a closer look.
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it was intentionally disabled in the header. #82
if you are going to add a realpath implementation anytime soon, it's great. please go ahead.
otherwise, it's probably better to revert this part for now, until the implementation gets ready.
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Reverting this part causes the libcxx build to fail, so I don't think that's an option (unless we want to patch libcxx). I've added a stub in #473, which I believe is the best we can do right now short of patching libcxx.
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Update: the stub wasn't needed -- turns out musl's realpath implementation works fine.
dicej
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In WebAssembly#463, I added stubs for `statvfs`, `chmod`, etc. but forgot to add one for `realpath`, which is also required by `libc++`'s `<filesystem>` implementation. Signed-off-by: Joel Dice <[email protected]>
sunfishcode
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* provide a `realpath` stub In #463, I added stubs for `statvfs`, `chmod`, etc. but forgot to add one for `realpath`, which is also required by `libc++`'s `<filesystem>` implementation. Signed-off-by: Joel Dice <[email protected]> * remove `realpath` stub and use musl's version instead Signed-off-by: Joel Dice <[email protected]> --------- Signed-off-by: Joel Dice <[email protected]>
rootbeer
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Point to the correct header files where the wasi-libc constants are defined that the Zig lib/std/c.zig is replicating. Zig's current copy of wasi-libc has a bug in the file-mode constants. Both S_IFIFO and S_IFSOCK are 0xc000, but S_IFIFO should be 0x1000. See WebAssembly/wasi-libc#463.
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Point to the correct header files where the wasi-libc constants are defined that the Zig lib/std/c.zig is replicating. Zig's current copy of wasi-libc has a bug in the file-mode constants. Both S_IFIFO and S_IFSOCK are 0xc000, but S_IFIFO should be 0x1000. See WebAssembly/wasi-libc#463.
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As of a recent fix included in LLVM 17[1] and wasi-libc fix[2], we can enable `LIBCXX_ENABLE_FILESYSTEM` in libcxx build for WebAssembly/WASI. This allows us to use `<filesystem>`, `<fstream>`, etc in C++ code. [1]: llvm/llvm-project@66a562d [2]: WebAssembly/wasi-libc#463
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wasi-libc 22 and later support realpath(3) (WebAssembly/wasi-libc#463) but the underlying host syscall may return ENOTSUP. This is typically the case when using incomplete WASI polyfills on web browsers. For such cases, we should fallback to the emulated realpath.
kateinoigakukun
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wasi-libc 22 and later support realpath(3) (WebAssembly/wasi-libc#463) but the underlying host syscall may return ENOTSUP. This is typically the case when using incomplete WASI polyfills on web browsers. For such cases, we should fallback to the emulated realpath.
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Per WebAssembly/wasi-sdk#373, LLVM's libc++ no longer allows us to enable
<fstream>and<filesystem>separately -- it's both or neither. Consequently, we either need to patch libc++ to not usestatvfs,chmod, etc. or add stub functions for those features towasi-libc. Since we're planning to eventually support those features with WASI Preview 2 and beyond, it makes sense to do the latter.Note that since libc++ uses
DT_SOCK, I've added a definition for it -- even though WASI Preview 1 does not define it. No Preview 1 file will ever have that type, so code that handles that type will never be reached, but defining it allows us to avoid WASI-specific patches to libc++.Related to
DT_SOCK, I had to change theS_IFIFOvalue so it does not conflict withS_IFSOCK, thereby avoiding ambiguity in__wasilibc_iftodt.