b85d65528d
* add stubs for dlopen, dlsym, etc. This adds weak exports for the POSIX `dlopen`, `dlsym`, `dlclose`, and `dlerror` functions, allowing code which uses those features to compile. The implementations are stubs which always fail since there is currently no official standard for runtime dynamic linking. Since the symbols are weak, they can be overriden with useful, runtime-specific implementations, e.g. based on host functions or statically-generated tables (see https://github.com/dicej/component-linking-demo for an example of the latter). Signed-off-by: Joel Dice <joel.dice@fermyon.com> * move `dlopen` stubs out of libc and into libdl Per review feedback, it's easier to simply replace libdl.so with a working implementation at runtime than it is to override a handful of symbols in libc. Note that I've both added libdl.so and replaced the empty libdl.a we were previously creating with one that contains the stubs. I'm thinking we might as well be consistent about what symbols the .so and the .a contain. Otherwise, e.g. the CPython build gets confused when the dlfcn.h says `dlopen` etc. exist but libdl.a is empty. Signed-off-by: Joel Dice <joel.dice@fermyon.com> * customize dlfcn.h for WASI For WASI, we use flag values which match MacOS rather than musl. This gives `RTLD_LOCAL` a non-zero value, avoiding ambiguity and allowing us to defer the decision of whether `RTLD_LOCAL` or `RTLD_GLOBAL` should be the default when neither is specified. We also avoid declaring `dladdr`, `dlinfo`, and friends on WASI since they are neither supported nor stubbed at this time. Signed-off-by: Joel Dice <joel.dice@fermyon.com> * use musl's RTLD_* flags except for RTLD_LOCAL This minimizes the divergence from upstream while still giving us the flexibility to choose a default value later. Signed-off-by: Joel Dice <joel.dice@fermyon.com> * use `NULL` instead of `0` for null pointers Signed-off-by: Joel Dice <joel.dice@fermyon.com> --------- Signed-off-by: Joel Dice <joel.dice@fermyon.com> |
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| CODE_OF_CONDUCT.md | ||
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wasi-libc
wasi-libc is a libc for WebAssembly programs built on top of WASI system
calls. It provides a wide array of POSIX-compatible C APIs, including support
for standard I/O, file I/O, filesystem manipulation, memory management, time,
string, environment variables, program startup, and many other APIs.
wasi-libc is sufficiently stable and usable for many purposes, as most of the
POSIX-compatible APIs are stable, though it is continuing to evolve to better
align with wasm and WASI. For example, pthread support is experimentally
provided via the wasi-threads proposal.`
Usage
The easiest way to get started with this is to use wasi-sdk, which includes a
build of wasi-libc in its sysroot.
Building from source
To build a WASI sysroot from source, obtain a WebAssembly-supporting C compiler (currently this is only clang 10+, though we'd like to support other compilers as well), and then run:
make CC=/path/to/clang/with/wasm/support \
AR=/path/to/llvm-ar \
NM=/path/to/llvm-nm
This makes a directory called "sysroot" by default. See the top of the Makefile for customization options.
To use the sysroot, use the --sysroot= option:
/path/to/wasm/supporting/c/compiler --sysroot=/path/to/the/newly/built/sysroot ...
to run the compiler using the newly built sysroot.
Note that Clang packages typically don't include cross-compiled builds of
compiler-rt, libcxx, or libcxxabi, for libclang_rt.builtins-wasm32.a,
libc++.a, or libc++abi.a, respectively, so they may not be usable without
extra setup. This is one of the things wasi-sdk simplifies, as it includes
cross-compiled builds of compiler-rt, libc++.a, and libc++abi.a.
Building in pthread support
To enable pthreads support via the wasi-threads proposal, follow the above
build directions with one addition: make ... THREAD_MODEL=posix. This creates
additional artifacts in sysroot/lib/wasm32-wasi-threads to support --target wasm32-wasi-threads.
Arch Linux AUR package
For Arch Linux users, there's an official wasi-libc package tracking this Git repository. You might want to install other WASI related packages as well.