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https://git.proxmox.com/git/wasi-libc
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9efc2f4283
* Lazy-initialize the environment variables. This is the first in a series of PRs to make it easier to use WASI libc in Wasm modules that don't have a `main` function. By initializing the environment on demand, we avoid depending on having `__wasm_call_ctors` run. This uses weak symbols strategically to ensure that if `environ` is used, it is initialized eagerly, but if only `getenv` and friends are used, the environment is initialized lazily. Eventually, I expect we'll have a convention for wasm modules without main functions which will allow the `__wasm_call_ctors` function to be called automatically, but this helps in simple cases for now. Fixes #180. * Add comments explaining the libc-environ-compat.h header usage.
78 lines
2.5 KiB
C
78 lines
2.5 KiB
C
#include <unistd.h>
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#include <stdlib.h>
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#include <sysexits.h>
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#include <wasi/api.h>
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#include <wasi/libc.h>
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#include <wasi/libc-environ.h>
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/// If the program doesn't use `environ`, it'll get this version of
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/// `__wasilibc_environ`, which isn't initialized with a constructor function.
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/// `getenv` etc. call `__wasilibc_ensure_environ()` before accessing it.
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/// Statically-initialize it to an invalid pointer value so that we can
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/// detect if it's been explicitly initialized (we can't use `NULL` because
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/// `clearenv` sets it to NULL.
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char **__wasilibc_environ __attribute__((weak)) = (char **)-1;
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// See the comments in libc-environ.h.
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void __wasilibc_ensure_environ(void) {
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if (__wasilibc_environ == (char **)-1) {
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__wasilibc_initialize_environ();
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}
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}
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/// Avoid dynamic allocation for the case where there are no environment
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/// variables, but we still need a non-NULL pointer to an (empty) array.
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static char *empty_environ[1] = { NULL };
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// See the comments in libc-environ.h.
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void __wasilibc_initialize_environ(void) {
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// Get the sizes of the arrays we'll have to create to copy in the environment.
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size_t environ_count;
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size_t environ_buf_size;
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__wasi_errno_t err = __wasi_environ_sizes_get(&environ_count, &environ_buf_size);
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if (err != __WASI_ERRNO_SUCCESS) {
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goto oserr;
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}
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if (environ_count == 0) {
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__wasilibc_environ = empty_environ;
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return;
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}
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// Add 1 for the NULL pointer to mark the end, and check for overflow.
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size_t num_ptrs = environ_count + 1;
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if (num_ptrs == 0) {
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goto software;
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}
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// Allocate memory for storing the environment chars.
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char *environ_buf = malloc(environ_buf_size);
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if (environ_buf == NULL) {
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goto software;
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}
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// Allocate memory for the array of pointers. This uses `calloc` both to
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// handle overflow and to initialize the NULL pointer at the end.
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char **environ_ptrs = calloc(num_ptrs, sizeof(char *));
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if (environ_ptrs == NULL) {
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free(environ_buf);
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goto software;
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}
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// Fill the environment chars, and the `__wasilibc_environ` array with
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// pointers into those chars.
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// TODO: Remove the casts on `environ_ptrs` and `environ_buf` once the witx is updated with char8 support.
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err = __wasi_environ_get((uint8_t **)environ_ptrs, (uint8_t *)environ_buf);
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if (err != __WASI_ERRNO_SUCCESS) {
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free(environ_buf);
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free(environ_ptrs);
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goto oserr;
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}
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__wasilibc_environ = environ_ptrs;
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return;
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oserr:
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_Exit(EX_OSERR);
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software:
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_Exit(EX_SOFTWARE);
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}
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