[LLVMdev] MachineCodeEmitter Patch

[Thomas Jablin]

Here is the corrected version.

Thomas Jablin wrote:
> Actually, there is a problem with the patch. Please delay review.
>
> Thomas Jablin wrote:
>   
>> Hi,
>> The following code:
>>
>> #include<stdio.h>
>>
>> char bigArray[0x1000000];
>>
>> int main(int argc, char **argv) {
>>  printf("mem: 0x%x\n", (unsigned) bigArray);
>>  return 0;
>> }
>>
>> causes lli to silently fail, even though it compiles correctly with 
>> llc.  The reason is that in JITEmitter.cpp only checks to see if 
>> CurBufferPtr == BufferEnd at the beginning of the function and not 
>> after all relocations have been handled. I have fixed this bug by 
>> adding an additional check after all relocations have been completed. 
>> In the process of fixing this bug, I happened to look through the code 
>> in MachineCodeEmitter.h.  The buffer size checks in 
>> MachineCodeEmitter.h all suffer from an integer overflow bug.  For 
>> example in allocateSpace the code reads:
>>
>>    // Allocate the space.
>>    CurBufferPtr += Size;
>>  
>>     // Check for buffer overflow.
>>    if (CurBufferPtr >= BufferEnd) {
>>
>> This is wrong because Size + CurBufferPtr can cause an integer 
>> overflow and thus appear to be less than BufferEnd.  The correct way 
>> to check for the end of a buffer is always:
>>
>> (Size >= BufferEnd-CurBufferPtr)
>>
>> This integer overflow bug causes the program:
>> #include<stdio.h>
>>
>> char b = 'b';
>> char c[0x8000000];
>>
>> int main(int argc, char **argv) {
>>  printf("%c\n", c[0]);
>>  return 0;
>> }
>> to segfault in lli.
>>
>> Finally, I have changed several instances of intptr_t to uintptr_t to 
>> avoid dangerous comparisons between signed and unsigned types. Code 
>> review of the enclosed patch would be greatly appreciated. Thanks
>> Tom
>> ------------------------------------------------------------------------
>>
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>>     
>
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