Ryan, can you do one final thing? When you run that program, be sure to specify `+RTS -Dl` (must be linked with -debug.) This will enable all the debug output where the linker is concerned. There will be a few hundred lines just for initialization (based on my machine.) If my theory is correct, you'll probably see stuff like 'Unloading object file ...' right as the invalid read/segfault occurs.
Hi Austin, I did this, and it produced a 97MB text file of debug output, the tail end of which was: *initLinker: idempotent return* *lookupSymbol: value of stg_gc_unpt_r1 is 0x485570* *`stg_gc_unpt_r1' resolves to 0x485570Reloc: P = 0x40b510f3 S = 0x485570 A = 0xfffffffffffffffc* *relocations for section 3 using symtab 8* *Rel entry 0 is raw( (nil) 0x800000001 (nil)) lookupSymbol: looking up base_ControlziApplicative_zdfApplicativeIO3_info* *initLinker: start* *initLinker: idempotent return* *lookupSymbol: value of base_ControlziApplicative_zdfApplicativeIO3_info is 0x40b51058* *`base_ControlziApplicative_zdfApplicativeIO3_info' resolves to 0x40b51058Reloc: P = 0x40b51100 S = 0x40b51058 A = (nil)* *resolveObjs: done* *lookupSymbol: looking up f* *initLinker: start* *initLinker: idempotent return* *lookupSymbol: value of f is 0x440330c0* *initLinker: start* *initLinker: idempotent return* *unloadObj: Test.o* *Checking whether to unload Test.o* *Unloading object file Test.o* And that's when it segfaulted (notusing valgrind). If it is of any use, here is the full output, which fortunately compresses down to 4.4MB: http://www.cs.indiana.edu/~rrnewton/temp/linker_unload_debug_output.txt.bz2 Best, -Ryan P.S. Here is the equivalent output from the same thing being run under valgrind: initLinker: idempotent return lookupSymbol: value of base_ControlziApplicative_zdfApplicativeIO3_info is 0x4c15058 `base_ControlziApplicative_zdfApplicativeIO3_info' resolves to 0x4c15058Reloc: P = 0x4c15100 S = 0x4c15058 A = (nil) resolveObjs: done lookupSymbol: looking up f initLinker: start initLinker: idempotent return lookupSymbol: value of f is 0x4c0f0c0 initLinker: start initLinker: idempotent return unloadObj: Test.o Checking whether to unload Test.o Unloading object file Test.o ==9030== Invalid read of size 8 ==9030== at 0x492502: checkUnload (CheckUnload.c:286) ==9030== by 0x476580: GarbageCollect (GC.c:666) ==9030== by 0x46ADCD: scheduleDoGC (Schedule.c:1652) ==9030== by 0x46B976: performGC_ (Schedule.c:2551) ==9030== by 0x46B9AE: performMajorGC (Schedule.c:2565) ==9030== by 0x4043E1: main (in /home/beehive/ryan_scratch/ghc-working/testsuite/tests/rts/linker_unload2) ==9030== Address 0x95c4580 is 80 bytes inside a block of size 120 free'd ==9030== at 0x4A063F0: free (vg_replace_malloc.c:446) ==9030== by 0x4656D5: stgFree (RtsUtils.c:107) ==9030== by 0x45DDF4: freeObjectCode (Linker.c:2087) ==9030== by 0x4924CF: checkUnload (CheckUnload.c:295) ==9030== by 0x476580: GarbageCollect (GC.c:666) ==9030== by 0x46ADCD: scheduleDoGC (Schedule.c:1652) ==9030== by 0x46B976: performGC_ (Schedule.c:2551) ==9030== by 0x46B9AE: performMajorGC (Schedule.c:2565) ==9030== by 0x4043E1: main (in /home/beehive/ryan_scratch/ghc-working/testsuite/tests/rts/linker_unload2) ==9030==