On Thu, Aug 5, 2010 at 11:42 AM, Matthew Knepley <knepley at gmail.com> wrote:
> On Thu, Aug 5, 2010 at 11:40 AM, Dmitry Karpeev <karpeev at mcs.anl.gov>wrote: > >> What is the intended behavior of PetscDLSym when called on an empty >> handle: PetscDLSym(handle=PETSC_NULL, symbol, &value) >> My understanding was that this should look for symbol in the symbol table >> of the main executable. >> This is based on what happens in the Windows case (#ifdef >> PETSC_HAVE_WINDOWS_H), >> but when using dlopen (#ifdef PETSC_HAVE_DLFCN_H), this probably won't >> behave correctly,as currently implemented. >> This is because the above call will boil down to >> value = dlsym((dlhandle_t)0, symbol), >> which on many systems returns NULL (e.g., on Ubuntu 9.10). >> There is a relatively easy fix, which is to obtain the handle of the main >> executable with, for example, >> dlhandle = dlopen(0,RTLD_LOCAL|RTLD_LAZY) >> followed by >> value = dlsym(dlhandle,symbol) >> >> I have played around with it on my box, and it appears to work. >> I can push that fix, if that's what we decide we want, and if it doesn't >> alter the currently expected behavior. >> There is one caveat: symbols can be dlsym'ed from the executable only if >> they are exported as dynamically-loadable, >> which is not the default behavior for linking executable (so as not to >> pollute the dynamic symbol table). >> On linux the linker needs to get -Wl,--export-dynamic, but it would be >> nice to enable some sort of portable option at compile time. >> > > This is sharedLinkerFlags. > Sorry, I meant configure-time option. Does sharedLinkerFlags alter the behavior of CLINKER? Unless there is another way to link an executable. Dmitry. > > Matt > > >> Incidentally, currently there appears to be no way to supply additional >> linker flags, as used to be the case with LDFLAGS. >> >> Dmitry. > > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which their > experiments lead. > -- Norbert Wiener > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20100805/b3fa10ca/attachment.html>