[LLVMdev] Weird behavior of llvm-ld

Bram Adams bram.adams at ugent.be
Wed Aug 16 09:01:57 PDT 2006


I'm using LLVM 1.8 with the GCC4-frontend on a Slackware 10.2 box (GCC 
3.3.6). When issuing the following command (line 14 in a script called 

llvm-ld -O1 *.trans -L${SOME_LIB_DIR} -L${SOME_OTHER_LIB_DIR} 
-load=${MY_LIB_DIR}/opt1.so -load=${MY_LIB_DIR}/opt2.so 
-debug-pass=Details -debug -o test

... I get the following messages:

llvm-ld: warning: Supposed library 'SOME_OTHER_LIB' isn't a library.
./manual.sh: line 14: 25492 Segmentation fault

When I invoke the same from within gdb, I get:

[Thread debugging using libthread_db enabled]
[New Thread -1210504992 (LWP 25520)]
llvm-ld: warning: Supposed library 'SOME_OTHER_LIB' isn't a library.

Program received signal SIGABRT, Aborted.
[Switching to Thread -1210504992 (LWP 25520)]
0xb7dbb027 in raise () from /lib/tls/libc.so.6

... with the following backtrace:

#0  0xb7dbb027 in raise () from /lib/tls/libc.so.6
#1  0xb7dbc747 in abort () from /lib/tls/libc.so.6
#2  0xb7eb6721 in uw_init_context_1 () from ${LLVM_FRONT}/lib/libgcc_s.so.1
#3  0xbf9fd140 in ?? ()
#4  0xbf9fcf20 in ?? ()
#5  0x00000064 in ?? ()
#6  0x082a02cd in llvm::Optimize (M=0x85bf330) at 
#7  0x082a7161 in main (argc=17, argv=0xbf9fd454, envp=0xbf9fd49c) at 

The exception raised apparently was not caused by the first warning 
message, but resulted from the following snippet of 
${LLVM_SRC}/tools/llvm-ld/Optimize.cpp (near line 180):

std::vector<std::string> plugins = LoadableModules;
for (std::vector<std::string>::iterator I = plugins.begin(), E = 
plugins.end(); I != E; ++I) {
    sys::DynamicLibrary dll(I->c_str());
    typedef void (*OptimizeFunc)(PassManager&,int);
    OptimizeFunc OF = OptimizeFunc(
    if (OF == 0) {
      throw std::string("Optimization Module '") + *I +
        "' is missing the RunOptimizations symbol";

The RunOptimizations-symbol is only mentioned briefly in the manual of 

-load module

    Load an optimization module, /module/, which is expected to be a
    dynamic library that provides the function name |RunOptimizations|.
    This function will be passed the PassManager, and the optimization
    level (values 0-5 based on the *-On* option). This function may add
    passes to the PassManager that should be run. This feature allows
    the optimization passes of *llvm-ld* to be extended.

Now, here are my two questions (finally ;-)) :

    * Why is SOME_OTHER_LIB not a library from llvm-ld's point of view?
      It's supposed to be a shared library needed by opt1.so (my first
      optimization pass), and NOT by the source files which are
      processed. Should I pass it in some other way than by
      -lSOME_OTHER_LIB? Should/Can I pass it in the first place?
    * What's the meaning of RunOptimizations? This name is only
      mentioned in the code snippet above and in the llvm-ld docs, but
      nowhere else. Both opt1.so and opt2.so do show up using opt, so it
      seems there is some incompatibility between opt and llvm-ld.
      llvm-link apparently offers no alternative.

Kind regards,

Bram Adams
GH-SEL, INTEC, Ghent University (Belgium)
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