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compiler: fix llvmcall segfault with zero-sized types #60111

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compiler: fix llvmcall segfault with zero-sized types #60111

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ea78ccf
ccall: add checks for zero-sized argument and return types in llvmcall
achaljhawar Nov 12, 2025
b955f00
fix: added trailing newline
achaljhawar Nov 12, 2025
16e8b2b
Merge branch 'JuliaLang:master' into fix-llvm-zero-args
achaljhawar Nov 12, 2025
ffc010f
fix: added void type check
achaljhawar Nov 12, 2025
376400d
Merge branch 'master' into fix-llvm-zero-args
achaljhawar Nov 13, 2025
ccbc646
Merge branch 'master' into fix-llvm-zero-args
achaljhawar Nov 15, 2025
6a02513
Merge branch 'master' into fix-llvm-zero-args
achaljhawar Nov 18, 2025
ea18a59
fix(llvmcall): prevent zero-sized return types from being emitted
achaljhawar Nov 18, 2025
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10 changes: 10 additions & 0 deletions src/ccall.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -909,6 +909,11 @@ static jl_cgval_t emit_llvmcall(jl_codectx_t &ctx, jl_value_t **args, size_t nar
jl_value_t *tti = jl_svecref(tt,i);
bool toboxed;
Type *t = julia_type_to_llvm(ctx, tti, &toboxed);
if (t == getVoidTy(ctx.builder.getContext())) {
emit_error(ctx, "llvmcall does not support zero-sized argument types");
JL_GC_POP();
return jl_cgval_t();
}
argtypes.push_back(t);
if (4 + i > nargs) {
emit_error(ctx, "Missing arguments to llvmcall!");
Expand All @@ -927,6 +932,11 @@ static jl_cgval_t emit_llvmcall(jl_codectx_t &ctx, jl_value_t **args, size_t nar
jl_value_t *rtt = rt;
bool retboxed;
Type *rettype = julia_type_to_llvm(ctx, rtt, &retboxed);
if (jl_is_datatype(rtt) && jl_datatype_size((jl_datatype_t*)rtt) == 0) {
emit_error(ctx, "llvmcall does not support zero-sized return types");
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@JeffBezanson JeffBezanson Nov 14, 2025

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What about void functions?

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@achaljhawar achaljhawar Nov 18, 2025

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added a check for that

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@vtjnash vtjnash Nov 18, 2025

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The semantics here of checking if the user made an egregious typo are still wrong. This is also well formed:

julia> mutable struct A end

julia> f() = Core.Intrinsics.llvmcall("ret ptr addrspace(10) null", A, Tuple{})

This sort of random checking for user error doesn't really make sense to me. The point of llvmcall is an unsafe escape hatch into unsafe territory. If you don't like that, just don't use it.

JL_GC_POP();
return jl_cgval_t();
}

// Make sure to find a unique name
std::string ir_name;
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6 changes: 6 additions & 0 deletions test/llvmcall.jl
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Expand Up @@ -218,3 +218,9 @@ s = MyStruct()
@test eltype(supertype(Core.LLVMPtr{UInt8,1})) <: UInt8
@test s.kern == 0
@test reinterpret(Int, s.ptr) == 0

f_zero_arg(x::T) where T = Base.llvmcall("ret i8 %0", Int8, Tuple{T}, x)
@test_throws ErrorException f_zero_arg(nothing)

f_zero_ret(x::Int8) = Base.llvmcall("ret void", Nothing, Tuple{Int8}, x)
@test_throws ErrorException f_zero_ret(Int8(1))