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| author | Sam Clegg <sbc@chromium.org> | 2022-04-14 15:41:15 +0000 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2022-04-14 15:41:15 +0000 |
| commit | c3a1ce092b888efbd234a7664f18e6bce977611d (patch) | |
| tree | 3a821aea11325bc4403772792ba449b62095b2b6 /wasm2c/README.md | |
| parent | 38953bfd87d9cfafccae2f5e93c4d2fd5949f2f0 (diff) | |
| download | wabt-c3a1ce092b888efbd234a7664f18e6bce977611d.tar.gz wabt-c3a1ce092b888efbd234a7664f18e6bce977611d.tar.bz2 wabt-c3a1ce092b888efbd234a7664f18e6bce977611d.zip | |
wasm2c: Always use a module prefix and set one by default (#1897)
The module prefix is no longer optional and is now set by default to the
name of the module as given in the name section, or taken from the name
of the input file.
A new `-n/--module-name` command line flag can also be used to override.
The prefix used by the generated code is now fixed at wasm2c time which
makes the output code easier to read and also avoid the symbol pasting
in the C pre-processor which makes the source hard to understand. For
example, it makes symbols hard to `grep` for.
Diffstat (limited to 'wasm2c/README.md')
| -rw-r--r-- | wasm2c/README.md | 55 |
1 files changed, 17 insertions, 38 deletions
diff --git a/wasm2c/README.md b/wasm2c/README.md index b68fe57a..ede6c787 100644 --- a/wasm2c/README.md +++ b/wasm2c/README.md @@ -45,26 +45,21 @@ files. ## Using the generated module -To actually use our fac module, we'll use create a new file, `main.c`, that +To actually use our `fac` module, we'll use create a new file, `main.c`, that include `fac.h`, initializes the module, and calls `fac`. -`wasm2c` generates a few symbols for us, `init` and `Z_fac`. `init` -initializes the module, and `Z_fac` is our exported `fac` function, but -[name-mangled](https://en.wikipedia.org/wiki/Name_mangling) to include the -function signature. +`wasm2c` generates a few C symbols based on the `fac.wasm` module. `Z_fac_init` +and `Z_fac_Z_fac`. The former initializes the module, and the later is our +exported `fac` function. -We can define `WASM_RT_MODULE_PREFIX` before including `fac.h` to generate -these symbols with a prefix, in case we already have a symbol called `init` (or -even `Z_fac`!) Note that you'll have to compile `fac.c` with this macro -too, for this to work. +All the exported symbols shared a common prefix (`Z_fac`) which, by default, is +based on the name section in the module or the name of input file. This prefix +can be overridden using the `-n/--module-name` command line flag. ```c #include <stdio.h> #include <stdlib.h> -/* Uncomment this to define fac_init and fac_Z_fac instead. */ -/* #define WASM_RT_MODULE_PREFIX fac_ */ - #include "fac.h" int main(int argc, char** argv) { @@ -78,12 +73,11 @@ int main(int argc, char** argv) { /* Initialize the Wasm runtime. */ wasm_rt_init(); - /* Initialize the fac module. Since we didn't define WASM_RT_MODULE_PREFIX, - the initialization function is called `init`. */ - init(); + /* Initialize the fac module. */ + Z_fac_init(); /* Call `fac`, using the mangled name. */ - u32 result = Z_fac(x); + u32 result = Z_fac_Z_fac(x); /* Print the result. */ printf("fac(%u) -> %u\n", x, result); @@ -135,10 +129,10 @@ extern "C" { #endif /* WASM_RT_INCLUDED_ */ -extern void WASM_RT_ADD_PREFIX(init)(void); +extern void Z_fac_init(void); /* export: 'fac' */ -extern u32 (*WASM_RT_ADD_PREFIX(Z_fac))(u32); +extern u32 (*Z_fac_Z_fac))(u32); #ifdef __cplusplus } #endif @@ -187,20 +181,6 @@ from stack-size exhaustion). This defaults to 500: #endif ``` -Next we can specify a module prefix. This is useful if you are using multiple -modules that may use the same name as an export. Since we only have one module -here, it's fine to use the default which is an empty prefix: - -```c -#ifndef WASM_RT_MODULE_PREFIX -#define WASM_RT_MODULE_PREFIX -#endif - -#define WASM_RT_PASTE_(x, y) x ## y -#define WASM_RT_PASTE(x, y) WASM_RT_PASTE_(x, y) -#define WASM_RT_ADD_PREFIX(x) WASM_RT_PASTE(WASM_RT_MODULE_PREFIX, x) -``` - Next are some convenient typedefs for integers and floats of fixed sizes: ```c @@ -342,17 +322,16 @@ provided called `init`, which initializes the module and must be called before the module can be used: ```c -extern void WASM_RT_ADD_PREFIX(init)(void); +extern void Z_fax_init(void); /* export: 'fac' */ -extern u32 (*WASM_RT_ADD_PREFIX(Z_fac))(u32); +extern u32 (*Z_facZ_fac)(u32); ``` -All exported names use `WASM_RT_ADD_PREFIX` (as described above) to allow the -symbols to placed in a namespace as decided by the embedder. All symbols are -also mangled so they include the types of the function signature. +All exported names use the mangled module name as a prefix (as described above) +to avoid collisions with other C symbols or symbols from other modules. -In our example, `Z_fac` is the mangling for a function named `fac`. +In our example, `Z_facZ_fac` is the mangling of the function named `fac`. ## A quick look at `fac.c` |