Value stack tag mismatch with the fast interpreter

[vouillon]

With #269, I still get an error with the fast interpreter on the attached program:

$ ./bin/wizeng.x86-64-linux  -ext:gc -ext:exception-handling ./print_array.wasm 
!X86_64StackError: value stack tag mismatch, expected ref, got 00
	in X86_64Stack.fatal() [src/engine/x86-64/X86_64Stack.v3 @ 462:29]
	in X86_64Stack.peekRef() [src/engine/x86-64/X86_64Stack.v3 @ 326:62]
	in X86_64Stack.popRef() [src/engine/x86-64/X86_64Stack.v3 @ 319:34]
	in X86_64Stack.pop() [src/engine/x86-64/X86_64Stack.v3 @ 310:70]
	in X86_64Stack.popV() [src/engine/x86-64/X86_64Stack.v3 @ 293:27]
	in Runtime.STRUCT_NEW() [src/engine/Runtime.v3 @ 42:47]
	in X86_64Runtime.runtime_STRUCT_NEW() [src/engine/x86-64/X86_64Runtime.v3 @ 244:42]
	in [fast-int] "toplevel"
	in [fast-int] "caml_main"
	in [fast-int] "entry_point"
	in [fast-int] #117
	in [return-parent-stub]
	in X86_64Stack.resume() [src/engine/x86-64/X86_64Stack.v3 @ 73:56]
	in X86_64StackManager.runOnFreshStack() [src/engine/x86-64/X86_64Stack.v3 @ 1009:62]
	in X86_64InterpreterOnlyStrategy.call() [src/engine/x86-64/X86_64Target.v3 @ 150:58]
	in Execute.call() [src/engine/Execute.v3 @ 18:36]
	in main() [src/wizeng.main.v3 @ 176:45]

The slow interpreter seems to work fine (after providing a dummy implementation for the WASI function random_get):

$ ./bin/wizeng.x86-linux -ext:gc -ext:exception-handling ./print_array.wasm 
empty
 0
misc
 1 2 3
end of tests

All tests succeeded.

[titzer]

Thanks, I'll take a look at this soon.

[titzer]

Looks like it was overwriting a register while decoding an unused part of a reference type local. With this change, the test program fails later with a failed cast (which I hope is right! :-))

[vouillon]

Well, looking at the diff between the traces of the slow and fast interpreter, it seems there is also an off by one error somewhere :)

--- ok.txt      2025-02-04 04:04:29.420647490 +0100
+++ bug.txt     2025-02-04 04:04:18.412609428 +0100
@@ -115698,21188 +115698,15 @@
         +67:  local.get[2]
         +69:  local.get[4]
         +71:  select[(ref eq)]
+        +74:  i32.div_s
         +75:  local.tee[1]
         +77:  call[func=24]
           +3:   local.get[0]
           +5:   ref.cast[i31]
-          +8:   i31.get_s
-          +10:  local.tee[1]
-          +12:  i32.const[0]
[...]
+<wasm func #117> +65
+  <wasm func "entry_point"> +1
+    <wasm func "caml_main"> +11
+      <wasm func "toplevel"> +936
+        <wasm func "create$1"> +77
+          <wasm func "caml_create_bytes"> +5
+            !trap[FAILED_CAST]

[titzer]

Oh, yes, I see now the fast interpreter does not decode value types in select properly (https://github.com/titzer/wizard-engine/blob/master/src/engine/x86-64/X86_64Interpreter.v3#L1008). I'll see if I can get a fix in later today or tomorrow.

[titzer]

See #277 .

[titzer]

Looks like I fixed the interpreter but the JIT still fails with a value tag mismatch.

% wizeng.x86-64-linux -mode=jit -ext:gc -ext:exception-handling print_array.wasm 
!X86_64StackError: value stack tag mismatch, expected: 7F, got 64
	in X86_64Stack.fatal() [src/engine/x86-64/X86_64Stack.v3 @ 462:29]
	in X86_64Stack.checkTopTag() [src/engine/x86-64/X86_64Stack.v3 @ 366:22]
	in X86_64Stack.popb32() [src/engine/x86-64/X86_64Stack.v3 @ 343:28]
	in X86_64Stack.pop() [src/engine/x86-64/X86_64Stack.v3 @ 297:55]
	in X86_64Stack.popV() [src/engine/x86-64/X86_64Stack.v3 @ 293:27]
	in Runtime.STRUCT_NEW() [src/engine/Runtime.v3 @ 42:47]
	in X86_64Runtime.runtime_STRUCT_NEW() [src/engine/x86-64/X86_64Runtime.v3 @ 244:42]
	in [spc-module] "caml_ml_open_descriptor_out"
	in [spc-module] "toplevel"
	in [fast-int] "caml_main"
	in [spc-module] "entry_point"
	in [spc-module] #117
	in [return-parent-stub]
	in X86_64Stack.resume() [src/engine/x86-64/X86_64Stack.v3 @ 73:56]
	in X86_64StackManager.runOnFreshStack() [src/engine/x86-64/X86_64Stack.v3 @ 1009:62]
	in X86_64ExecutionStrategy.call() [src/engine/x86-64/X86_64Target.v3 @ 136:58]
	in Execute.call() [src/engine/Execute.v3 @ 18:36]
	in main() [src/wizeng.main.v3 @ 176:45]