#3347: Add flag to prevent generation of import libraries on Windows
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Reporter: batterseapower | Owner:
Type: feature request | Status: new
Priority: normal | Component: Compiler
Version: 6.10.2 | Severity: normal
Keywords: | Testcase:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
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The import libraries generated when you use the -shared option to generate
a library can be very big. For example, when using it to build the edit-
distance library from Hackage (v0.1.2) I observed a DLL size of 2.7Mb and
an import library size of 2.2Mb. (See also http://www.nabble.com/--out-
implib-when-linking-shared-libraries-tt23561017.html)
Due to these size concerns, it may be desirable to disable the generation
of the import library altogether in cases where the user only wants to use
dynamic linking. The attached patch adds a new flag, -fno-shared-implib,
that does just that.
NB: after experimentation I have found that there are at least two ways to
reduce the size of the generated import library:
* Use pexports from mingw-utils to generate a .def file from the
generated .dll, and then use lib /def:<deffile> to generate an import
library from that. (NB: may be an issue with underscores added/removed in
exported names - I haven't checked this). This generated a 825kb import
library in my experiment above.
* Unpack the .dll.a generated by the binutils ld and link the contents
together. This should be equally functional as an import library, but it
reduces the disk space requirements to a similar level as the other option
(815kb in my test).
The basic root of the problem is that the import libraries generated by
GNU dlltool / ld are pretty bloated compared to those from the Microsoft
toolchain. However, even the MS toolchain can't do much better than 30% of
the size of the code, because Haskell code just exports tons of symbols
(~3200 in my test, which of course includes not only the library but the
RTS, base library etc). This should be ameliorated by the implementation
of shared libraries on Windows.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3347>
GHC <http://www.haskell.org/ghc/>
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