sbc100
commented
4 years ago Hi danec020,
The short answer to you question is that youprobably want to use
the new way to create standalone wasm modules: -s STANDALONE_WASM.
Using SIDE_MODULE to achieve this is probably a bad idea because it generates relocation code which you probably don't need for your use case.
There is some documentation here: https://github.com/emscripten-core/emscripten/wiki/WebAssembly-Standalone
I should mention that emscripten is very aggressive a DCE (dead code
elimination) so
in -Os mode it will already strip away any JS code or wasm code that you
don't explicitly
use/need.
cheers. sam
On Sun, Nov 24, 2019 at 11:45 AM danec020 notifications@github.com wrote:
I am following a book and trying to learn WebAssembly but things have obviously changed since the book was written. I am trying to create an exported C++ project that doesn't use the standard library and instead uses my own functions. That way we can strip the unneeded includes out. This is the method I am using to compile the code. I am also doing the JS code myselft to understand creating promises and importing the wasm files.
Here is the old example's generated WAT file compared to the newly generated WAT file. You can see that the global fields of an int and a struct are exported as functions for some reason. At the end is the cpp file that has these exports. Any help on how I can prevent this if it is not supposed to happen or how should I correctly import them in the Promise? At the very bottom is my import code in JS.
Compile script emcc side_module_system_functions.cpp validate.cpp -s WASM_ASYNC_COMPILATION=0 -s SIDE_MODULE=2 -O1 -o validate.wasm
Old Exported Wasm imports
(module (type (;0;) (func (param i32 i32 i32))) (type (;1;) (func (param i32) (result i32))) (type (;2;) (func (param i32))) (type (;3;) (func (param i32 i32) (result i32))) (type (;4;) (func (param i32 i32 i32 i32) (result i32))) (type (;5;) (func (param i32 i32 i32) (result i32))) (type (;6;) (func)) (import "env" "__memory_base" (global (;0;) i32)) (import "env" "memory" (memory (;0;) 256))
New Exported WASM imports
(module (type (;0;) (func)) (type (;1;) (func (param i32 i32 i32))) (type (;2;) (func (param i32) (result i32))) (type (;3;) (func (param i32))) (type (;4;) (func (param i32 i32) (result i32))) (type (;5;) (func (param i32 i32 i32) (result i32))) (type (;6;) (func (param i32 i32 i32 i32) (result i32))) (type (;7;) (func (result i32))) (import "env" "g$AllocatedMemoryChunks" (func $g$AllocatedMemoryChunks (type 7))) (import "env" "g$current_allocated_count" (func $g$current_allocated_count (type 7))) (import "env" "__memory_base" (global (;0;) i32)) (import "env" "memory" (memory (;0;) 0))
The CPP file with the problematic exports, side_module_system_functions.cpp
include
include
ifdef __cplusplus
extern "C" { // So that the C++ compiler does not rename our function names
endif
const int TOTAL_MEMORY = 65536; // We should always have at least 1 page of memory (1,024 bytes x 64 KiB). const int MAXIMUM_ALLOCATED_CHUNKS = 10; int current_allocated_count = 0;
struct MemoryAllocated { int offset; int length; };
struct MemoryAllocated AllocatedMemoryChunks[MAXIMUM_ALLOCATED_CHUNKS];// The array that will hold details about each memory allocation
// Helper when adding an item before existing items in the array void InsertIntoAllocatedArray(int new_item_index, int offset_start, int size_needed) { // Shift everything to the right by one if it is to the right of where the new item will be inserted for (int i = (MAXIMUM_ALLOCATED_CHUNKS - 1); i > new_item_index; i--) { AllocatedMemoryChunks[i] = AllocatedMemoryChunks[(i - 1)]; }
// Add the new item at the specified index AllocatedMemoryChunks[new_item_index].offset = offset_start; AllocatedMemoryChunks[new_item_index].length = size_needed; // Increment the count of blocks allocated current_allocated_count++;}
// Our version of malloc EMSCRIPTEN_KEEPALIVE int create_buffer(int size_needed) { // If we are already at our limit of allocated memory blocks then exit now if (current_allocated_count == MAXIMUM_ALLOCATED_CHUNKS) { return 0; }
// Adjust the start position to give room for items that will be copied into memory when the module is instantiated int offset_start = 1024; int current_offset = 0; int found_room = 0; int memory_size = size_needed; while (memory_size % 8 != 0) { memory_size++; }// Increase the size so that the next offset will be a multiple of 8 // Loop through the currently allocated memory... for (int index = 0; index < current_allocated_count; index++) { // If there is space between the previous offset and the current one for the memory that is wanted then... current_offset = AllocatedMemoryChunks[index].offset; if ((current_offset - offset_start) >= memory_size) { // Add the current item to the current index of the array (bump the rest of the items to the right by one) InsertIntoAllocatedArray(index, offset_start, memory_size); found_room = 1; break; } // OffsetStart for the next loop will be the end of the current array item's memory block offset_start = (current_offset + AllocatedMemoryChunks[index].length); } // Room wasn't found in between the existing allocated memory blocks if (found_room == 0) { // If there is room between the end of the last memory block and the end of memory then... if (((TOTAL_MEMORY - 1) - offset_start) >= size_needed) { // Add the item to the array AllocatedMemoryChunks[current_allocated_count].offset = offset_start; AllocatedMemoryChunks[current_allocated_count].length = size_needed; current_allocated_count++; found_room = 1; } } // If there was room for the memory needed then return the offset if (found_room == 1) { return offset_start; } // Otherwise, tell the caller there was no room (NULL pointer) return 0;}
JavaScript Import Promise
let moduleMemory = null; let moduleExports = null;
function initializePage() { document.getElementById("name").value = initialData.name;
const category = document.getElementById("category"); const count = category.length; for (let index = 0; index < count; index++) { if (category[index].value === initialData.categoryId) { category.selectedIndex = index; break; } }
moduleMemory = new WebAssembly.Memory({initial: 256});
const importObject = { env: { __memory_base: 0, memory: moduleMemory, } };
WebAssembly.instantiateStreaming(fetch("validate.wasm"), importObject).then(result => { moduleExports = result.instance.exports; }); }
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danec020
kripken
stale[bot]
I am following a book and trying to learn WebAssembly but things have obviously changed since the book was written. The old WASM file works fine but when exporting with the latest version it does not. The new version wants to import two field as functions for some reason.
I am trying to create an exported C++ project that doesn't use the standard library and instead uses my own functions. That way we can strip the unneeded includes out. I am running into a problem where AllocatedMemoryChunks field is being exported as a function and the browser console is saying in the promise I am missing a callable. I am creating the JS code myself as part of the learning process. I am creating an import object with my memory import information but I am not sure how to set it up to work with the AllocatedMemoryChunks.
Here is the old example's generated WAT file compared to the newly generated WAT file. You can see that the global fields of an int and a struct are exported as functions for some reason. At the end is the cpp file that has these exports. Any help on how I can prevent this if it is not supposed to happen or how should I correctly import them in the Promise? At the very bottom is my import code in JS.
Compile script
emcc side_module_system_functions.cpp validate.cpp -s SIDE_MODULE=2 -O1 -o validate.wasmOld Exported Wasm imports
New Exported WASM imports
The CPP file with the problematic exports, side_module_system_functions.cpp
JavaScript Import Promise