wasm/setjmp.h

   1 #ifndef RB_WASM_SUPPORT_SETJMP_H
   2 #define RB_WASM_SUPPORT_SETJMP_H
   3
   4 #include "ruby/internal/config.h"
   5 #include <stdbool.h>
   6
   7 #ifndef WASM_SETJMP_STACK_BUFFER_SIZE
   8 # define WASM_SETJMP_STACK_BUFFER_SIZE 6144
   9 #endif
  10
  11 struct __rb_wasm_asyncify_jmp_buf {
  12     void* top;
  13     void* end;
  14     char buffer[WASM_SETJMP_STACK_BUFFER_SIZE];
  15 };
  16
  17 typedef struct {
  18     // Internal Asyncify buffer space to save execution context
  19     struct __rb_wasm_asyncify_jmp_buf setjmp_buf;
  20     // Internal Asyncify buffer space used while unwinding from longjmp
  21     // but never used for rewinding.
  22     struct __rb_wasm_asyncify_jmp_buf *longjmp_buf_ptr;
  23     // Used to save top address of Asyncify stack `setjmp_buf`, which is
  24     // overwritten during first rewind.
  25     void *dst_buf_top;
  26     // A payload value given by longjmp and returned by setjmp for the second time
  27     int payload;
  28     // Internal state field
  29     int state;
  30 } rb_wasm_jmp_buf;
  31
  32 // noinline to avoid breaking Asyncify assumption
  33 NOINLINE(int _rb_wasm_setjmp(rb_wasm_jmp_buf *env));
  34 NOINLINE(void _rb_wasm_longjmp(rb_wasm_jmp_buf *env, int payload));
  35
  36 #define rb_wasm_setjmp(env) ((env).state = 0, _rb_wasm_setjmp(&(env)))
  37
  38 // NOTE: Why is `_rb_wasm_longjmp` not `noreturn`? Why put `unreachable` in the call site?
  39 // Asyncify expects that `_rb_wasm_longjmp` returns its control, and Asyncify inserts a return
  40 // for unwinding after the call. This means that "`_rb_wasm_longjmp` returns its control but the
  41 // next line in the caller (C level) won't be executed".
  42 // On the other hand, `noreturn` means the callee won't return its control to the caller,
  43 // so compiler can assume that a function with the attribute won't reach the end of the function.
  44 // Therefore `_rb_wasm_longjmp`'s semantics is not exactly same as `noreturn`.
  45 #define rb_wasm_longjmp(env, payload) (_rb_wasm_longjmp(&env, payload), __builtin_unreachable())
  46
  47 // Returns the Asyncify buffer of next rewinding if unwound for setjmp capturing or longjmp.
  48 // Used by the top level Asyncify handling in wasm/runtime.c
  49 void *rb_wasm_handle_jmp_unwind(void);
  50
  51
  52 //
  53 // POSIX-compatible declarations
  54 //
  55
  56 typedef rb_wasm_jmp_buf jmp_buf;
  57
  58 #define setjmp(env) rb_wasm_setjmp(env)
  59 #define longjmp(env, payload) rb_wasm_longjmp(env, payload)
  60
  61
  62 typedef void (*rb_wasm_try_catch_func_t)(void *ctx);
  63
  64 struct rb_wasm_try_catch {
  65     rb_wasm_try_catch_func_t try_f;
  66     rb_wasm_try_catch_func_t catch_f;
  67     void *context;
  68     int state;
  69 };
  70
  71 //
  72 // Lightweight try-catch API without unwinding to root frame.
  73 //
  74
  75 void
  76 rb_wasm_try_catch_init(struct rb_wasm_try_catch *try_catch,
  77                        rb_wasm_try_catch_func_t try_f,
  78                        rb_wasm_try_catch_func_t catch_f,
  79                        void *context);
  80
  81 // Run, catch longjmp thrown by run, and re-catch longjmp thrown by catch, ...
  82 //
  83 // 1. run try_f of try_catch struct
  84 // 2. catch longjmps with the given target jmp_buf or exit
  85 // 3. run catch_f if not NULL, otherwise exit
  86 // 4. catch longjmps with the given target jmp_buf or exit
  87 // 5. repeat from step 3
  88 //
  89 // NOTICE: This API assumes that all longjmp targeting the given jmp_buf are NOT called
  90 // after the function that called this function has exited.
  91 //
  92 void
  93 rb_wasm_try_catch_loop_run(struct rb_wasm_try_catch *try_catch, rb_wasm_jmp_buf *target);
  94
  95 #endif