[LLVMbugs] [Bug 9779] New: Code from C backend compiled with GCC crashes due to calling functions through pointers to a different function types

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=9779

           Summary: Code from C backend compiled with GCC crashes due to
                    calling functions through pointers to a different
                    function types
           Product: new-bugs
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: maemarcus at gmail.com
                CC: llvmbugs at cs.uiuc.edu


Consider the following original code line:

fprintf(stdout, "this fprintf is involved into crash\n");

LLVM translates it to the following IR:

%6 = call i64 bitcast (i64 (i8*, i64, i64, %struct._IO_FILE*)* @fwrite to i64
(i8*, i64, i64, i8*)*)(i8* getelementptr inbounds ([37 x i8]* @.cst2, i64 0,
i64 0), i64 1, i64 36, i8* %5) nounwind

And C backend generates a similar line of C code:

llvm_cbe_tmp__5 = ((unsigned long long  (*) (unsigned char *, unsigned long
long , unsigned long long , unsigned char
*))(void*)fwrite)(((&_OC_cst2.array[((signed long long )0ull)])), 1ull, 36ull,
(((unsigned char *)llvm_cbe_tmp__4)));

Now, compiled with gcc, we have:

warning: function called through a non-compatible type
note: if this code is reached, the program will abort

And resulting program will crash with SIGILL (Illegal instruction).

Although, the problem seems to be specific to gcc and specific to code
generation approach involving C backend instead of direct asm generation, it
would be better to make LLVM more accurate about functions typecasting.

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