[LLVMdev] symbols for exception handling

[Reed Kotler]

I'm working on a patch for this problem for mips16; unfortunately it's a 
target independent patch.

I'm not sure the best nomenclature for this.

In the gcc mips16 patch they call "xxx=." a debug label.
The other terminology they use is byte pointer vs ISA-encoded address 
(ISA-encoded meaning this one bit in the case of mips16 ISA).

I'm planning to add a virtual method called EmitDebugLabel to MCStreamer
which just calls method EmitLabel.

Because of some luck, for exception handling at least, I really only 
need to EmitDebugLabel for eh_func_beginXX.

The other entries in the exception table are all a-b, except for 
eh_func_beginXX, the 1 bits will cancel each other out. I don't know if 
this is sufficient for actual dwarf info for debugging; i have not 
thought through this yet.

The real solution that gcc uses is to distinguish these two kinds of 
labels everywhere.

On 11/02/2012 07:53 PM, reed kotler wrote:
> mips16 has some unusual requirements for label symbols in .s.
>
> I think that arm thumb has the same issue but have not located yet how
> this is handled.
>
> When you have a label of an instruction in mips16, when you reference
> the label, the linker
> adds a 1 to the address. When you call an odd numbered address, the
> procesor switches to mips16 mode and when you call an even numbered
> address it switches to mips32 mode.
>
> This causes some problems in the exception tables.
>
> Basically, labels that are not landing pad symbols that are inserted for
> exception handling
> and dwarf purposes, must declared :
>
> $mysym = .
>
> as opposed to:
>
> $mysym:
>
> Has this problem of making this distinction already been solved in llvm
> and if so, how is this done?
>
> Tia.
>
> Reed