On Thursday 11 June 2009 22:22:13 Oleg Goldshmidt wrote: > Shlomi Fish <shlo...@iglu.org.il> writes: > > Hi all! > > > > Based on the gcc-4.4.0 (with -Os) / x86-Linux shared library sizes > > here: > > > > http://tech.groups.yahoo.com/group/fc-solve-discuss/message/998 > > > > And the Visual C++/Win32 (also x86) .dll sizes here: > > > > http://tech.groups.yahoo.com/group/fc-solve-discuss/message/999 > > > > My question is: why are the Visual C++ generated binaries so much > > smaller than the equivalent Linux ones? Any insights would be > > appreciated. > > Shlomi, > > The short answer is, I don't know. I didn't even try to figure out > where the apples and the oranges were in your fc-solve-discuss > postings. Since you don't list files and sizes (at least not in any > way I can decipher, being unfamiliar with the project) or specify how > you compile and link (apart from -Os), I don't know if you compare > apples to apples.
I've compared the size of the Linux .so file (after -Os and strip) to the size of the Windows MSVC-generated .dll. With gcc -Os before strip - 86,464 bytes same after strip - 74,584 With gcc -Os that can solve Freecell only - before strip: 71,440 After strip - 60,312 Now on Windows, Visual C++ generated the files in: http://tech.groups.yahoo.com/group/fc-solve-discuss/message/999 I have some freecell-solver.dll's there and since it is the output of cygwin's "ls -l", you can determine their size. The Freecell-only DLL after strip is 18,944 bytes long. > > I'll assume you compare dynamically linked executables on Linux/gcc > and on Windows/cl, and the corresponding so and dll libraries. I'm only interested in the shared-libraries/DLLs. I should note that from what I tried MinGW's gcc (rather old) also generates relatively large .so files (that's what I ended up with - don't know if they are valid DLLs), on Windows (Same computer as the one I have Visual C++ on). Hopefully, I'll play with it more tomorrow. > > I'll wave my hands wildly and offer a couple of guesses that you can > try to investigate. They may be completely off the mark. > > 1) You probably know that DLLs work differently from Linux shared > libraries. DLLs contain relocatable code that uses a preferred base > address to which the loader will want to map the file. If a process > is linked against several libraries all but one need to be > relocated to other free addresses, COW-ed while fixing the addresses, > independently paged, etc. This also means that DLLs are dynamically > loaded, but not shared (they can only be shared between processes > with the same memory layout). Linux shared libraries contain > position-independent code (PIC) that uses only relative (to the > program counter) addresses. These libraries are really shared. > > PIC implies address translation tables that are filled at load > time, but I suppose they are allocated at link time. This may be > one source of size overhead. I have no idea how important this > overhead is, you need to consult the experts. > > There are (or at least used to be) -fPIC and -fpic options to > GCC. IIRC, -fpic implied a limit on the size of translation tables, > and refused to build if the resulting tables were too large. In > comparison, -fPIC implies no limits. However, I seem to recall that > the limits were quite small. OK, I'll try. > > 2) I suppose that the structure of the code is important. E.g., does > your optimization include inlining? Inlining replicates code, > objects, etc., hence it may affect something. I am not sure if -Os > overrides inlining. I am using inlining. However, Visual C++ also respects that (via its ANSI C __inline keyword that I'm using). Maybe it does a better job with it with MinSizeRel than gcc does. > > 3) Do you use exceptions a lot? IIRC, GCC generates stack unwinding > information for each function that may throw an exception (unless > something changed - you are using a recent version). This > information is stored in the executable. I don't know if the MS > compiler does the same thing. I don't have any exceptions. This is ANSI C code. Regards, Shlomi Fish -- ----------------------------------------------------------------- Shlomi Fish http://www.shlomifish.org/ "Star Trek: We, the Living Dead" - http://xrl.us/omqz4 God gave us two eyes and ten fingers so we will type five times as much as we read. _______________________________________________ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
