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Subject: [Boost-build] [gcc] separate debug infos
From: Juergen Hunold (juergen.hunold_at_[hidden])
Date: 2009-01-21 15:20:44

Hi !

I've stumpled across a trick used by Qt's qmake to reduce the size of
library and executables. Qt's configure --help calls this
"-separate-debug-info .... Strip debug information into a separate
.debug file."

This will (theoretically) lead to faster startup times, especially when
using release builds with debug-symbols enabled (my default).
The basic trick is to use "objcopy" from GNU bintutils to separate the
debug information and create a hint for the debugger where to look for
them in case of emergency :-))

Short description:
1. Copy only debug symbols to <file>.debug
2. Strip only debug symbols from <file>
3. Add debug link to <file>.debug to <file>
4. Cleanup (make <file>.debug non-executable

I've attached a brute-force, hardcoded implementation of this algorithm.
It uses a new toolset feature <objcopy> to specify which objcopy shall
be used (needed for cross-compilation).

This proof of concept works (for me), but now comes the hard part:
I've got no idea how to _really_ incorporate this into the current gcc
toolchain. The way would be:
- introduce a new feature "separate-debug-info : off on ;"
- if this feature is "on", add a post link step which will execute steps
1-4 above.
- introduce a new feature "install-separate-debug-info" to the "install"
rule (needed if you want to have everything ready for packaging etc.).

Ideas on how to implement this are welcome.



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