wasm object stuff

gistfile1.txt

Here's some C code:

void extern_func(int *, int*, int*, int*);

static int static_var = 3;
int global_var = 4;
extern int extern_var;

__attribute__((noinline))
static void static_func(void)
{
  static_var = 5;
}

void normal_func(void)
{
  int stack_var;
  extern_func(&stack_var, &static_var, &global_var, &extern_var);
  static_func();
}

Compile it like: clang --target=wasm32-unknown-unknown-wasm -O2 -c t.c

Running wasm2wast on the t.o file currently doesn't work, because LLVM's relocation records
differ a little from wabt's, but if I manually remove those sections for now, wasm2wast
prints the following. I've annotated it with some comments.

(module
  (type (;0;) (func))
  (type (;1;) (func (param i32 i32 i32 i32)))
  (import "env" "extern_var" (global (;0;) i32))            ;; a global import; the global isn't actually used; this just provides an index for use in relocation
  (import "env" "extern_func" (func extern_func (type 1)))  ;; a function import; this is actually used, in addition to being used for relocations
  (func normal_func (type 0)
    (local i32)
    get_global 0     ;; read the stack pointer
    i32.const 16
    i32.sub
    tee_local 0
    set_global 0     ;; write the stack pointer (our local copy is in local 0)
    get_local 0
    i32.const 12
    i32.add          ;; stack_var (local 0 holds the stack pointer value. plus an offset)
    i32.const 0      ;; static_var; the 0 is the actual linear memory offset within this module, but we also have a reloc so we can link it with other modules
    i32.const 4      ;; global_var; the 4 is ... ditto ...
    i32.const -1     ;; extern_var; the -1 is a placeholder the linker will need to patch
    call extern_func
    call static_func
    get_local 0
    i32.const 16
    i32.add
    set_global 0)    ;; restore the original stack pointer value
  (func static_func (type 0)
    i32.const 0
    i32.const 5
    i32.store)
  (table (;0;) 0 anyfunc) ;; this module has no literal function addresses, so the table is empty (that may change if this module is linked with other modules)
  (memory (;0;) 8)
  (global (;1;) (mut i32) (i32.const 0))    ;; the stack-pointer global
  (global (;2;) i32 (i32.const 4))          ;; global_var's global (when the new-and-improved name section arrives, we'll be able to name this instead of just calling it "0" everywhere)
  (export "normal_func" (func normal_func)) ;; a normal function export
  (export "global_var" (global 2))          ;; an export of the global for global_var
  (data (i32.const 0) "\03\00\00\00\04\00\00\00")) ;; the data containing static_var and then global_var