On Tue, Aug 20, 2002 at 09:25:06PM +0200, Luca Barbieri wrote: > I propose to do the following to solve the libpng2/3 problem. I've > recompiled libpng2. libpng3 and libgtk2.0-0png3 locally and the system > seems to work correctly. > 1. Recompile libpng2 and libpng3 with -Bsymbolic > 2. Recompile all libraries that use either libpng2 or libpng3 to > explicitly link to them and to use -Bsymbolic > 3. Recompile all programs that use either libpng2 or libpng3 to > explicitly link to them [all programs should already do > this] > 4. Make either libgtk2.0-0 or libgtk2.0-0png3 a dummy package > depending on the other > Note1: for GTK+ 2.0, only the png loader plugin needs to be recompiled > with -Bsymbolic > Note2: "recompile with -Bsymbolic" means "add -Wl,-Bsymbolic to the > flags passed to the compiler in the linking stage, rebuild and upload > the new package" > Doing this will allow applications using GTK+ to use either libpng2 or > libpng3 and still work correctly. > I'll now explain what the problem is and why this solution works. > The problem is that libpng2 and libpng3 have symbols with different > names and we want to have both loaded in the same address space. > Symbols are resolved by the GNU dynamic linker, part of glibc, that > normally uses the same search list for all modules. > This means that normally when two symbols have the same name everything > will use the symbol in the first module loaded. > What we instead want is to use the symbol in the library that the > calling module links to. >sing -Bsymbolic ensures that whenever the libpng library makes a call to one of its own functions, the symbol is resolved internally instead of to another version of libpng that's loaded. This may account for a majority of the segfaults that people are seeing. It does not affect how symbols are resolved when something /outside/ of libpng tries to call a function belonging to libpng. If the ABI has changed between libpng2 and libpng3 (which it supposedly has), there is still a danger of segfaults whenever both of these libraries are loaded into memory -- with or without -Bsymbolic. Steve Langasek postmodern programmer
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