[LLVMdev] load bytecode from string for jiting problem
Vikas Bhargava
vikasbhargava at gmail.com
Wed Mar 19 14:11:53 PDT 2014
Hi Willy,
If the disassembly of the module works fine, then there is nothing wrong
with the module.
Stream uses the memorybuffer that you pass in parseBitcodeFile. If what
Will is saying is true, there is something wrong with your code in "3:",
i.e.:
MemoryBuffer* mbjit = MemoryBuffer::getMemBuffer (sr.str());
LLVMContext& context = getGlobalContext();
ErrorOr<Module*> ModuleOrErr = parseBitcodeFile (mbjit, context);
if (error_code EC = ModuleOrErr.getError())
{
std::cout << ModuleOrErr.getError().
message() << "\n";
assert(false);
}
Can you post how you modified it in your second reply? For debugging
purpose, you can simply use MemoryBuffer::getMemBufferCopy() and not worry
about validity of stringref or null-termination. Also, you can run your
program through valgrind and check for any invalid reads.
HTH
Vikas.
=======
On Wed, Mar 19, 2014 at 10:32 AM, Willy WOLFF <willy.wolff at etu.unistra.fr>wrote:
> I mad the change, and still have the problem.
>
> I investigate more the source code of llvm.
>
> First, I change isRawBitcode function to print the content of the
> parameter like this:
> original: http://llvm.org/docs/doxygen/html/ReaderWriter_8h_source.
> html#l00081
>
> inline bool isRawBitcode(const unsigned char *BufPtr,
> const unsigned char *BufEnd) {
> // These bytes sort of have a hidden message, but it's not in
> // little-endian this time, and it's a little redundant.
> errs()<< "isRawBitcode output:\n";
> for (int i = 0; i < 4; i++)
> errs() << BufPtr[i] << "\n";
> if (BufPtr != BufEnd )
> errs() << "BP != BE ok\n";
> if (BufPtr[0] == 'B')
> errs() << "B ok\n";
> if (BufPtr[1] == 'C')
> errs() << "C ok\n";
> if (BufPtr[2] == 0xc0)
> errs() << "0xc0 ok\n";
> if (BufPtr[3] == 0xde)
> errs() << "0xde ok\n";
>
> return BufPtr != BufEnd &&
> BufPtr[0] == 'B' &&
> BufPtr[1] == 'C' &&
> BufPtr[2] == 0xc0 &&
> BufPtr[3] == 0xde;
> }
>
>
> Second, I change ParseBitcodeInto as this:
> original: http://llvm.org/docs/doxygen/html/BitcodeReader_8cpp_
> source.html#l01971
> ...
> errs() << "parsebitcodeinto sniff the signature\n";
> uint32_t bvar = Stream.Read(8);
> errs() << "B :" << bvar << "\n";
> if (bvar != 'B') {
> errs() << "B :" << bvar << "\n";
> return Error(InvalidBitcodeSignature);
> }
>
> if (Stream.Read(8) != 'C') {
> errs() << "C\n";
> return Error(InvalidBitcodeSignature);
> }
> if ( Stream.Read(8) != 0xc0 ) {
> errs() << "0xc0\n";
> return Error(InvalidBitcodeSignature);
> }
> if ( Stream.Read(8) != 0xde ) {
> errs() << "0xde\n";
> return Error(InvalidBitcodeSignature);
> }
> // if (Stream.Read(8) != 'B' ||
> // Stream.Read(8) != 'C' ||
> // Stream.Read(4) != 0x0 ||
> // Stream.Read(4) != 0xC ||
> // Stream.Read(4) != 0xE ||
> // Stream.Read(4) != 0xD
> // ) {
> ...
>
>
>
> The output of the code is :
>
>
> isRawBitcode output:
> B
> C
>
>
> BP != BE ok
>
> B ok
> C ok
> 0xc0 ok
> 0xde ok
>
> parsebitcodeinto sniff the signature
> B :37
> B :37
>
>
>
>
> It's possible that Stream object is not correctly initialized?
>
>
> On 03/13/2014 06:37 PM, Will Dietz wrote:
>
>> On Thu, Mar 13, 2014 at 9:02 AM, Willy WOLFF <willy.wolff at etu.unistra.fr>
>> wrote:
>>
>>> Hello,
>>>
>>> I having a weird problem while writing a bytecode module to a string,
>>> and after read/parse it for unsing on a jit.
>>>
>>> I write a pass to export function to module, and put this module inside
>>> a global variable.
>>> I use WriteBitcodeToFile for this.
>>> For debuging, after this write, I try to load the exported module with
>>> parseBitcodeFile.
>>> This two step works.
>>>
>>>
>>>
>>> After, while the compiled program is running, I try to read and parse
>>> this global variable for jiting the function.
>>>
>>> 1) I read the global variable with
>>> StringRef sr (gv, gv_length);
>>>
>>> 2) I manually test this bytecode by
>>> (inspired by inline bool isRawBitcode(const unsigned char *BufPtr,
>>> const unsigned char *BufEnd) at
>>> http://llvm.org/docs/doxygen/html/ReaderWriter_8h_source.html#l00067)
>>> if (sr.str()[0] == 'B')
>>> std::cout << "B ok\n";
>>> if (sr.str()[1] == 'C')
>>> std::cout << "C ok\n";
>>> if (sr.str()[2] == (char) 0xc0)
>>> std::cout << "0xc0 ok\n";
>>> if (sr.str()[3] == (char) 0xde)
>>> std::cout << "0xde ok\n";
>>>
>>> 3) I try to parse the gv by
>>> MemoryBuffer* mbjit = MemoryBuffer::getMemBuffer (sr.str());
>>>
>>
>> Not sure if this is your issue, but should be fixed anyway:
>>
>> The std::string created by "sr.str()" ends its lifetime in this
>> statement, and MemoryBuffer for efficiency reasons
>> avoids copying data it doesn't have to (like StringRef) so will be
>> referencing the freed memory.
>>
>> To resolve this:
>> * Pass MemoryBuffer your StringRef directly
>> * Use getMemBufferCopy()
>> * Preserve the result of sr.str() into a stack variable and pass that
>> to getMemoryBuffer() instead.
>>
>> As a final note, check if your bitcode buffer "string" is
>> null-terminated or not. If not, be sure to be careful and
>> do things like informing MemoryBuffer that this is the case.
>>
>> Hope this helps,
>> ~Will
>>
>> LLVMContext& context = getGlobalContext();
>>> ErrorOr<Module*> ModuleOrErr = parseBitcodeFile (mbjit, context);
>>> if (error_code EC = ModuleOrErr.getError())
>>> {
>>> std::cout << ModuleOrErr.getError().message() << "\n";
>>> assert(false);
>>> }
>>>
>>>
>>>
>>>
>>> This is the execution result:
>>> B ok
>>> C ok
>>> 0xc0 ok
>>> 0xde ok
>>> Invalid bitcode signature
>>>
>>>
>>>
>>> Ok is not working :/
>>> But why ???
>>>
>>>
>>>
>>> For debuging, between 2) and 3), I export the readed module and write to
>>> a file on my hard drive,
>>> and try llvm-dis, and the dissasembly of the module works.
>>>
>>> Wath's wrong? Any idea for solve this problem?
>>>
>>> Thanks you very much.
>>>
>>> Regards,
>>> Willy
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>
>> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
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