wiki:Commentary/Rts/Cmm

Version 3 (modified by guest, 8 years ago) (diff)

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GHC Commentary: What the hell is a .cmm file?

A .cmm file is rather like C--. The syntax is almost C-- (a few constructs are missing), and it is augmented with some macros that are expanded by GHC's code generator (eg. INFO_TABLE()). A .cmm file is compiled by GHC itself: the syntax is parsed by compiler/cmm/CmmParse.y and compiler/cmm/CmmLex.x into the Cmm data type, where it is then passed through one of the back-ends.

We use the C preprocessor on .cmm files, making extensive use of macros to make writing this low-level code a bit less tedious and error-prone. Most of our C-- macros are in includes/Cmm.h.

Additions over C--

The .cmm syntax includes the

foreign "C" cfunctionname(R1) [R2];

I think the [R2] part is the (set of) register(s) that you need to save over the call.