I figured that there might be others out there who are trying to figure
out how to write a personality function, so I've attached the one I have
written as an example. The code is straight ANSI C.
I used the GCC version as a reference, but I re-wrote most of it, and
made the syntax more like the LLVM style. I also drew from a number of
other personality functions for other languages that I found out on the
web. One thing I did was to cut down on the complexity by making the
code LLVM-specific - for example, I only included decoding functions for
those encodings that are actually emitted by LLVM.
The personality function uses type descriptors from my language (Tart)
rather than C++ std::type_info objects, and tests the exception type
using my language's own isSubclass() method. This can serve as an
example for how to use exceptions for languages that are different from C++.
To invoke the personality function and have it catch an exception, the
IR that you generate should look like the following:
try:
;; Throw some exception
invoke { } @"throwSomething"() to label %endTry unwind label %catch
catch:
;; Catch and decode the exception
%eh_ptr = call i8* @llvm.eh.exception()
%eh_action = call i32 (i8*, i8*, ...)* @llvm.eh.selector.i32(
i8* %eh_ptr,
i8* bitcast (i32 (i32, i32, i64, i8*, i8*)* @__tart_eh_personality
to i8*),
%tart.reflect.Type* @tart.core.InvalidArgumentException.type,
%tart.reflect.Type* @tart.core.Throwable.type)
;; subtract offset of UnwindExceptInfo member within class Throwable
%0 = bitcast i8* %eh_ptr to [0 x i8]*
%eh_throwable = getelementptr [0 x i8]* %0, i32 0,
i32 sub (i32 0, i32 ptrtoint (%2* getelementptr (
%tart.core.Throwable* null, i32 0, i32 2) to i32))
;; Branch based on action from personality func.
switch i32 %eh_action, label %catch-InvalidArgumentException [
i32 0, label %catch-InvalidArgumentException
i32 1, label %catch-Throwable
]
catch-InvalidArgumentException:
;; Cast to caught type
%bitcast = bitcast i8* %eh_throwable to
%tart.core.InvalidArgumentException*
br label %endTry
catch-Throwable: ; preds = %catch
;; Cast to caught type
%bitcast9 = bitcast i8* %eh_throwable to %tart.core.Throwable*
br label %endTry
-- Talin
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