For some cross-compile configurations (where the host platform is Cygwin), the
cygpath program is used to convert file names from the build platform
notation to the Cygwin form (technically, this conversion is from Windows
notation to Cygwin notation; the conversion from the build platform format
to Windows notation is performed via other means). However, because the
cygpath program is not (and should not be) in the PATH on
the build platform, LT_CYGPATH must specify the full build platform
file name (that is, the full Unix or MSYS file name) of the cygpath
program.
The reason cygpath should not be in the build platform PATH is
twofold: first, cygpath is usually installed in the same directory as
many other Cygwin executables, such as sed, cp, etc. If
the build platform environment had this directory in its PATH, then these
Cygwin versions of common Unix utilities might be used in preference to the
ones provided by the build platform itself, with deleterious effects. Second,
especially when Cygwin-1.7 or later is used, multiple Cygwin installations can
coexist within the same Windows instance. Each installation will have separate
“mount tables” specified in CYGROOT-N/etc/fstab. These
mount tables control how that instance of Cygwin will map Windows file
names and paths to Cygwin form. Each installation’s cygpath utility
automatically deduces the appropriate /etc/fstab file. Since each
CYGROOT-N/etc/fstab mount table may specify different mappings, it
matters what cygpath is used.
Note that cygpath is a Cygwin application; to execute this tool from
Unix requires a working and properly configured Wine installation, as well
as enabling the GNU/Linux binfmt extension. Furthermore, the Cygwin
setup.exe tool should have been used, via Wine, to properly install
Cygwin into the Wine file system (and registry).
Unfortunately, Wine support for Cygwin is intermittent. Recent releases of
Cygwin (1.7 and above) appear to require more Windows API support than Wine
provides (as of Wine version 1.2); most Cygwin applications fail to execute.
This includes cygpath itself. Hence, it is best not to use
the LT_CYGPATH machinery in libtool when performing Unix to Cygwin
cross-compiles. Similarly, it is best not to enable the GNU/Linux binfmt
support in this configuration, because while Wine will fail to execute the
compiled Cygwin applications, it will still exit with status zero. This tends
to confuse build systems and test suites (including libtool’s own testsuite,
resulting in spurious reported failures). Wine support for the older
Cygwin-1.5 series appears satisfactory, but the Cygwin team no longer supports
Cygwin-1.5. It is hoped that Wine will eventually be improved such that
Cygwin-1.7 will again operate correctly under Wine. Until then, libtool will
report warnings as described in see File Name Conversion Failure in these
scenarios.
However, LT_CYGPATH is also used for the MSYS to Cygwin cross compile
scenario, and operates as expected.