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| Differential D34172
[WebAssembly] Use __stack_pointer global when writing wasm binary ClosedPublic Authored by sbc100 on Jun 13 2017, 2:11 PM.
Details Summary This ensures that symbolic relocations are generated for SP The relocations are of type R_WEBASSEMBLY_GLOBAL_INDEX_LEB Since its a globally imported symbol this does mean that
Diff Detail
Event TimelineHerald added subscribers: jgravelle-google, dschuff, jfb. · View Herald TranscriptJun 13 2017, 2:11 PM Comment Actions If you like I could probably split out the part of this change that is generally adding support for R_WEBASSEMBLY_GLOBAL_INDEX_LEB. Comment Actions This looks like a good idea. It was awkward trying to track global variable indices in the MachineModuleInfo. In fact, you can just remove the MachineModuleInfoWasm class entirely now, unless you have another use for it. This revision is now accepted and ready to land.Jun 16 2017, 11:15 AM Closed by commit rL305616: [WebAssembly] Use __stack_pointer global when writing wasm binary (authored by sbc). · Explain WhyJun 16 2017, 4:59 PM This revision was automatically updated to reflect the committed changes. Comment Actions Could you clarify what the __stack_pointer expects from the external code. **//Edit://** Never mind. I found the clarification to the __stack_pointer problem here: https://github.com/WebAssembly/tool-conventions/blob/master/DynamicLinking.md#interface-and-usage. Just needed to understand what the pointer was referring to. Giving a high enough initial value as an offset in the linear memory object for the stack, solves the problem. Leaving the original question below. Just in case someone is having the same problem. I generated .wasm code for accessing a struct defined in c++ and when trying to run the corresponding code from the wasm module imported into a javascript file. I end up getting a "bus error:10". Simpler codes where the __stack_pointer is not used work fine. To make things more concrete, I have a c++ code like: // c++ code
struct foo {
double a;
double b;
}
double f(double x){
foo r;
r.b = x;
return 0.0;
}This generates a wasm file of the form (module
(type $t1 (func (param f64) (result f64)))
(import "env" "__linear_memory" (memory $env.__linear_memory 0))
(import "env" "__indirect_function_table" (table $env.__indirect_function_table 0 funcref))
(import "env" "__stack_pointer" (global $env.__stack_pointer (mut i32)))
...
(func $f (type $t1) (param $p0 f64) (result f64)
(local $l1 i32) (local $l2 f64)
global.get $env.__stack_pointer
i32.const 32
i32.sub
local.tee $l1
global.set $env.__stack_pointer
local.get $l1
...
)
(export "f" (func $f))
...and so on, using the __stack_pointer load and store values onto a stack. However it's not clear as to what the stack object is when referenced from the external file. For example, if I instantiate the corresponding wasm file from a javascript as shown below, it leads to crash with "bus error:10" displayed in the terminal: // js file to load module
const http = require('http');
const fs = require('fs');
const buf = fs.readFileSync('foo.wasm');
var typedbuf = new Uint8Array(buf);
const env = {
__linear_memory: new WebAssembly.Memory({initial:256}),
__indirect_function_table: new WebAssembly.Table({initial:0,element:'anyfunc'}),
__stack_pointer: new WebAssembly.Global({value:'i32', mutable:true}, 0)
}
WebAssembly.instantiate(typedbuf,{env:env}).then(res=>console.log(res.instance.exports.f(4))).catch(e => {
// error caught
console.log(e);
});
...Here the WebAssembly.instantiate, defines the imports in "env" and includes a "_ _stack_pointer" as a WebAssembly.Global object. However this doesn't seem to work as stated previously.
Revision Contents
Diff 102908 llvm/trunk/include/llvm/CodeGen/MachineModuleInfoImpls.h
llvm/trunk/lib/CodeGen/MachineModuleInfoImpls.cpp
llvm/trunk/lib/MC/WasmObjectWriter.cpp
llvm/trunk/lib/Object/WasmObjectFile.cpp
llvm/trunk/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp
llvm/trunk/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.h
llvm/trunk/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.cpp
llvm/trunk/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyWasmObjectWriter.cpp
llvm/trunk/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
llvm/trunk/lib/Target/WebAssembly/WebAssemblyFrameLowering.cpp
llvm/trunk/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp
llvm/trunk/test/CodeGen/WebAssembly/byval.ll
llvm/trunk/test/CodeGen/WebAssembly/reg-stackify.ll
llvm/trunk/test/CodeGen/WebAssembly/stack-alignment.ll
llvm/trunk/test/CodeGen/WebAssembly/userstack.ll
llvm/trunk/test/MC/WebAssembly/func-address.ll
llvm/trunk/test/MC/WebAssembly/stack-ptr.ll
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