Translate function pointers passed in variadic arguments#83
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nunoplopes
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May 12, 2026
| if (expr->getType()->isFunctionPointerType()) { | ||
| StrCat("std::mem::transmute::<*mut ::libc::c_void", token::kComma); | ||
| Convert(expr->getType()); | ||
| StrCat(">"); |
nunoplopes
reviewed
May 12, 2026
| pub unsafe fn apply_unary_3(mut x: i32, args: &[VaArg]) -> i32 { | ||
| let mut ap: VaList = VaList::default(); | ||
| ap = VaList::new(args); | ||
| let mut fn_: Option<unsafe fn(i32) -> i32> = std::mem::transmute::< |
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Why is Option needed here?
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We translate functions pointers to Option<fn> in unsafe. Option is needed to encode nullability
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In unsafe, the function pointer is first converted to void* when passed to a variadic function. Then, inside the variadic function, when calling
va_arg(ap, fn_ptr), the function is first retrieved as void*, then transmuted to function pointer. Thefunction pointer -calling variadic function-> void*, void* -va_arg(ap, fn_ptr)-> transmute<function pointer>is needed so that we don't add the unsafe transmute in libcc2rs.In refcount, this dance is not needed. VaArg and VaArgGet are implemented for FnPtr safely.