The R for Windows Build Process
===============================

from the point of view of a Unix installer of R.

Compilation of C/Fortran code is done in two pathways.

1) standard and add-on packages, the most similar to Unix.

The primary Makefiles are
$(R_HOME)/etc${R_ARCH}/Makeconf
share/make/winshlib.mk

included in that order.  Some settings in Makeconf are substituted in
etc/Makeconf by fixed/Makefile, taken from MkRules.


2) Everything else, where the primary Makefile is MkRules which is
where all the customization is done.  This is included by all
Makefile.win files in directories above this one and

./Makefile
./fixed/Makefile
./front-ends/Makefile
./getline/Makefile
./installer/Makefile

and replaces Unix's top-level Makeconf.


The largest difference from Unix (even a R-shlib build) is the use of
DLLs, which require the exported symbols to be listed (via nm) in a
.def file and fed to the compiler with the object files for linking.

In recent years DLLs are linked to directly as libraries, but there
remains provision for import libraries via lib%.dll.a: %.def rules.

Making executables has a number of Windows-specific features, done in
front-ends/Makefile:

- A resource compiler is used to compile in version information, an
  icon and a manifest.  Also done for version information in all the
  other DLLs under bin and modules (R.dll Rblas.dll Rgraphapp.dll
  Riconv.dll Rlapack.dll lapack.dll).

- LINKFLAGS includes flags for the stack size and to allow addressing
  over 2GB for 32-bit executables.

A resource compiler is used to add version information to the DLLs
under directories bin and modules.

The default is to compile without debug info: this can be enabled by
using 'make DEBUG=T' from this directory, or install add-on packages
with Rcmd INSTALL --debug.  Otherwise DLLs and executables are
stripped.


Link-Time Optimization
======================

To enable LTO for building R set the LTO macro in MkRules.local, to
-flto or e.g. -flto=8 to use 8 threads.

Checking of packages with LTO can be performed by setting the LTO_OPT
macro to -flto in MkRules.local and using Rcmd INSTALL --use-LTO.

For an installed version of R it should suffice to edit the value of
LTO_OPT in the etc/*/Makeconf files or to set it in a personal or site
Makevars file.

[Unlike a Unix-alike, LTO/LTO_OPT are used for Fortran as well as C/C++.]


Cross-compilation
=================

The instructions which were here were for R <= 4.1, and have not yet
been rewriten for the UCRT-based build used for 4.2.