|Version 2 (modified by 10 years ago) (diff),|
GHC Commentary: The Code Generator
Storage manager representations
The code generator needs to know the layout of heap objects, because it generates code that accesses and constructs those heap objects. The runtime also needs to know about the layout of heap objects, because it contains the garbage collector. How can we share the definition of storage layout such that the code generator and the runtime both have access to it, and so that we don't have to keep two independent definitions in sync?
Currently we solve the problem this way:
- C types representing heap objects are defined in the C header files, see for example includes/Closures.h.
- A C program, includes/mkDerivedConstants.c,
#includesthe runtime headers. This program is built and run when you type
includes/. It is run twice: once to generate
includes\DerivedConstants.h, and again to generate
- The file
DerivedConstants.hcontains lots of
#define OFFSET_StgTSO_why_blocked 18which says that the offset to the why_blocked field of an
StgTSOis 18 bytes. This file is
#includedinto includes/Cmm.h, so these offests are available to the hand-written .cmm files.
- The file
GHCConstants.hcontains similar definitions:
oFFSET_StgTSO_why_blocked = 18::IntThis time the definitions are in Haskell syntax, and this file is
#includeddirectly into compiler/main/Constants.lhs. This is the way that these offsets are made available to GHC's code generator.