#8935: Obscure linker bug leads to crash in GHCi -------------------------------------+------------------------------------ Reporter: simonmar | Owner: simonmar Type: bug | Status: infoneeded Priority: high | Milestone: 7.8.3 Component: Runtime System | Version: 7.8.1-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: GHCi crash | Difficulty: Rocket Science Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by dagit): Simon, at the moment I'm just trying to understand this whole thing better myself. My uncertainty is in these areas: * How the `dlsym()` search should work. For example, I'm not sure if `dlsym()` is supposed to look in the `NEEDED` dependencies or not. It seems to look in them. * Whether glibc implements the above search correctly. * Finally, I have no idea what is the right way to fix ghc's linker. I assume you're already familiar with the elf linking spec, but here is the link just to make sure we're looking at the same doc: http://refspecs.linuxbase.org/elf/elf.pdf It says: * STB_LOCAL Local symbols are not visible outside the object file containing their definition. Local symbols of the same name may exist in multiple files without interfering with each other. * STB_GLOBAL Global symbols are visible to all object files being combined. One file's definition of a global symbol will satisfy another file's undefined reference to the same global symbol. * STB_WEAK Weak symbols resemble global symbols, but their definitions have lower precedence. I'd say, based on what I see on my machine that `WEAK` seems to be even lower priority than `LOCAL`. It's interesting that your ld-linux.so doesn't have `environ`, when I grep mine I get these hits: {{{ $ readelf -Wa /usr/lib64/ld-linux-x86-64.so.2 | grep environ 143: 0000000000000000 0 FILE LOCAL DEFAULT ABS dl-environ.c 179: 0000000000000000 0 FILE LOCAL DEFAULT ABS environ.c 268: 00000031e4022168 8 OBJECT LOCAL DEFAULT 21 _environ 275: 00000031e4022168 8 OBJECT LOCAL DEFAULT 21 __environ 300: 00000031e4022168 8 OBJECT LOCAL DEFAULT 21 environ }}} For your libgmp.so does `environ` get defined in any of the deps listed by `ldd`? The `dlsym` manpage has this (potentially) interesting comment:
External references in the library are resolved using the libraries in that library's dependency list and any other libraries previously opened with the RTLD_GLOBAL flag. If the executable was linked with the flag "-rdynamic" (or, synonymously, "--export-dynamic"), then the global symbols in the executable will also be used to resolve references in a dynamically loaded library.
Please let me know if there is more I can do to help. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8935#comment:21 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler