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A general description is here.
‘R CMD INSTALL’ has a new option ‘--dsym’ which on Mac OS X (Darwin) dumps the symbols alongside the ‘.so’ file: this is helpful when debugging with ‘valgrind’ (and especially when installing packages into ‘R.framework’). [This can also be enabled by setting the undocumented environment variable ‘PKG_NAKE_DSYM’, since R 2.12.0.]