[llvm-bugs] [Bug 35385] New: WASM backend generates invalid wasm for undeclared imports

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=35385

            Bug ID: 35385
           Summary: WASM backend generates invalid wasm for undeclared
                    imports
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: WebAssembly
          Assignee: unassignedbugs at nondot.org
          Reporter: ncw at realvnc.com
                CC: llvm-bugs at lists.llvm.org

When the WASM backend generates a call to an incomplete function declaration,
it generates illegal WASM.

Testcase below:


#### test.c ####

// Succeeds, with (void) annotation
// Generates import with "(func)" type
extern void externSym1(void);
void exportSym1() { externSym1(); }

// Fails!
// Generates import with "(func (param i32))" type, but
// calls the imported function with the signature "void()".
extern void externSym2();
void exportSym2() { externSym2(); }


#### Commands ####
# $LLVM/clang --version
clang version 6.0.0 (trunk 318652)
Target: wasm32-unknown-unknown-wasm
Thread model: posix

# $LLVM/clang -Oz -c -o test.o test.c

# $WABT/wasm2wat test.o
0000000: error: type mismatch in call, expected [i32] but got []



The expected result (perhaps) is that the WASM backend refuses to generate
calls to functions with in incomplete declaration? But then how is linking to
varargs functions supposed to work? Hmm, I'm a bit confused really, but it
surely can't be right that the WASM output is invalid.

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