Ömer Sinan Ağacan
Hi,
Currently debugging Cmm is a bit painful because we don't have enough debug information to map assembly to Cmm lines, so I have do the mapping manually. However I realized that when building .cmm files we actually generates some debug information, in form of "ticks":
//tick src
_c2e::I64 = I64[R1 + 32]; Here the tick says that this assignment is for this Cmm line in Apply.cmm:
Words = StgAP_STACK_size(ap);
I was wondering what needs to be done to generate DWARF information from those so that gdb can show Cmm line we're executing, and gdb commands like `next`, `break` etc. work.
The DWARF information that we produce are indeed derived from these source notes. If you compile a C-- module with -g3 you will find the resulting object file should have line number information.
I also realize that we don't consistently generate these ticks for all Cmm lines, for example, in the same Cmm dump there isn't a tick before this line:
Indeed the C-- parser doesn't produce as many source notes as you might find in C-- from the STG pipeline. Essentially it only adds source notes on flow control constructs and assignments (see uses of withSourceNote in CmmParse.y). However, there is also a slightly more fundamental issue here: GHC's NCG handles DWARF information with block granularity. Fixing this will be a bit more involved. See compiler/nativeGen/Dwarf.hs for details. One alternative would be to just finish debug information in the LLVM backend and use this instead (originally D2343, although mpickering has a newer version). Cheers, - Ben