Segmentation fault when calling cglobal inside a function

[ronisbr]

Hi!

I need to get an exported symbol from a library inside a function. The following code works fine:

macOS

julia> libc = dlopen("libc")
Ptr{Nothing} @0x000000010ed40ff8

julia> cglobal(dlsym(libc,:atol))
Ptr{Nothing} @0x00007fff77b084ed

Linux

julia> libc = dlopen("libc.so.6")
Ptr{Nothing} @0x00007fa04fe803c0

julia> cglobal(dlsym(libc,:atol))
Ptr{Nothing} @0x00007fa04f73af70

However, if I put the very same code inside a function, then I get a segmentation fault:

macOS

julia> function teste()
       libc = dlopen("libc")
       cglobal( dlsym( libc, :sin), Cvoid )
       end
teste (generic function with 1 method)

julia> teste()

signal (11): Segmentation fault: 11
in expression starting at REPL[2]:1

Linux

julia> using Libdl

julia> function teste()
       libc = dlopen("libc.so.6")
       cglobal(dlsym(libc,:atol))
       end
teste (generic function with 1 method)

julia> teste()

signal (11): Falha de segmentação
in expression starting at REPL[3]:1
_ZNK4llvm5Value10getContextEv at /usr/bin/../lib64/julia/libLLVM-6.0.so (unknown line)
_ZN4llvm5Value11setNameImplERKNS_5TwineE at /usr/bin/../lib64/julia/libLLVM-6.0.so (unknown line)
_ZN4llvm5Value7setNameERKNS_5TwineE at /usr/bin/../lib64/julia/libLLVM-6.0.so (unknown line)
CreateLoad at /home/abuild/rpmbuild/BUILD/julia-1.2.0/usr/include/llvm/IR/IRBuilder.h:68
emit_varinfo at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/codegen.cpp:3516
emit_expr at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/codegen.cpp:3564
emit_call at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/codegen.cpp:3249
emit_expr at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/codegen.cpp:4029
interpret_symbol_arg at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/ccall.cpp:569
emit_cglobal at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/ccall.cpp:677 [inlined]
emit_intrinsic at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/intrinsics.cpp:877
emit_call at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/codegen.cpp:3243
emit_expr at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/codegen.cpp:4029
emit_ssaval_assign at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/codegen.cpp:3734
emit_function at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/codegen.cpp:3926
jl_compile_linfo at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/codegen.cpp:1196
jl_compile_method_internal at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/gf.c:1775
jl_apply_generic at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/gf.c:2196
do_call at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/interpreter.c:323
eval_value at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/interpreter.c:411
eval_stmt_value at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/interpreter.c:362 [inlined]
eval_body at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/interpreter.c:754
jl_interpret_toplevel_thunk_callback at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/interpreter.c:884
unknown function (ip: 0xfffffffffffffffe)
unknown function (ip: 0x7effd3c4d68f)
unknown function (ip: 0xffffffffffffffff)
jl_interpret_toplevel_thunk at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/interpreter.c:893
jl_toplevel_eval_flex at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/toplevel.c:815
jl_toplevel_eval_flex at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/toplevel.c:764
jl_toplevel_eval_in at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/toplevel.c:844
eval at ./boot.jl:330
eval_user_input at /home/abuild/rpmbuild/BUILD/julia-1.2.0/usr/share/julia/stdlib/v1.2/REPL/src/REPL.jl:86
macro expansion at /home/abuild/rpmbuild/BUILD/julia-1.2.0/usr/share/julia/stdlib/v1.2/REPL/src/REPL.jl:118 [inlined]
#26 at ./task.jl:268
jl_apply at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/julia.h:1614 [inlined]
start_task at /home/abuild/rpmbuild/BUILD/julia-1.2.0/src/task.c:596
unknown function (ip: 0xffffffffffffffff)
Allocations: 2334197 (Pool: 2333643; Big: 554); GC: 4
Falha de segmentação (imagem do núcleo gravada)
ronan.arraes@install:~/.julia/dev/TextUserInterfaces/src/ncurses> 

Everything works if I declare libc as global. Is it expected?

[jmert]

I just came across this issue as well. The minimal(ish) case I produced (using the libccalltest.so library from Julia's tests):

import Libdl: dlopen, dlsym, dlpath
const global_var = Ref{Cint}()
cd(dirname(dlpath("libjulia.so")))

function works()
    lib = dlopen("libccalltest.so")
    sym = dlsym(lib, :global_var)
    ref = cglobal(sym, Cint)
    global_var[] = unsafe_load(ref)
end
function segfaults()
    lib = dlopen("libccalltest.so")
    ref = cglobal(dlsym(lib, :global_var), Cint)
    global_var[] = unsafe_load(ref)
end

function fn1()
    lib = dlopen("libccalltest.so")
    sym = dlsym(lib, :ctest)
    return ccall(sym, Complex{Int}, (Complex{Int},), 0 + 0im)
end
function fn2()
    lib = dlopen("libccalltest.so")
    return ccall(dlsym(lib, :ctest), Complex{Int}, (Complex{Int},), 0 + 0im)
end

The latter two functions (fn1 and fn2) were me testing that having an inline dlsym call within a ccall was allowed — I know that otherwise the tuple of libname/function has to be a literal and not a tuple-valued variable, but I wasn't off-hand sure about the allowed syntax for passing in a pointer. Then since the cglobal docs say "...specified exactly as in ccall", I take that to mean that the same construct should work for a cglobal as well, so the first two functions works and segfaults use similar syntax to grab a global.

I've also found that you can inspect segfaults down to as far as @code_typed optimize=true segfaults(), but if you try to go one step further to @code_llvm optimize=false segfaults() Julia crashes.