[LLVMbugs] [Bug 4483] New: The JIT allocates global data inside of function bodies, which can be freed

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=4483

           Summary: The JIT allocates global data inside of function bodies,
                    which can be freed
           Product: new-bugs
           Version: unspecified
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: new bugs
        AssignedTo: reid.kleckner at gmail.com
        ReportedBy: reid.kleckner at gmail.com
                CC: llvmbugs at cs.uiuc.edu


Consider the program:

int counter = 0;
void foo() { return ++counter; }
void bar() { return ++counter; }

If we use the JIT, and make a call to foo, free the code for foo, and then call
bar, we'll access freed memory.  Of course, you won't notice the problem until
something else is allocated in the freed region, but if you poison freed memory
it's easier to detect.

This also interferes with reattempting to JIT machine code, which I was working
on when I found this bug.  I ran into it because I free the machine code before
retrying, and if the function allocated any globals before reattempting, the
old addresses are saved in the GlobalValue to address map.

I've attached a failing test case, and I'm working on a fix.


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