Re: Issue in LLDB's Expression Parser
Re: Issue in LLDB's Expression Parser
- Subject: Re: Issue in LLDB's Expression Parser
- From: Andreas Grosam <email@hidden>
- Date: Thu, 28 Jul 2011 11:35:17 +0200
On Jul 27, 2011, at 7:33 PM, Jim Ingham wrote:
> lldb uses clang as its expression parser. There can be some subtle differences because at present we always run Clang in ObjC++ mode.
>
> But in this case, I'm not sure what you are seeing, but I get:
>
>> cat foo.cpp
> #include <stdio.h>
> #include <stdint.h>
>
> int main ()
> {
> uint8_t c = 0;
> bool value = (c - 0xC2) < 0x32;
> if (value)
> printf ("True.\n");
> else
> printf ("False.\n");
>
> return 0;
> }
>> clang++ -g -O0 -o foo foo.cpp
>> ./foo
> True.
>
> I'm not sure what you are seeing that is different.
Hm, after verifying what I have stated, I have to admit I am wrong. Firstly, the result from clang is correct, which shall be "true" in this case. Secondly, I can't see any difference in lldb's result and the result from clang.
So, I probably did overlook a difference in my code and in the expression I entered into lldb. In the morning this appears crystal clear now, and I can't say what I have overlooked.
Sorry for that noise.
Andreas
> Jim
>
>
> On Jul 27, 2011, at 4:16 AM, Andreas Grosam wrote:
>
>> Hi All,
>>
>>
>> I figured an issue in the expression parser of LLDB.
>>
>> Firstly, I'm not sure if LLDB uses its own parser or if it's based somehow on LLVM. Anyway, here is the problem:
>>
>> LLDB prints the following result for the given expression:
>> (lldb) print ((uint8_t)(0) - 0xC2) < 0x32
>> (_Bool) $2 = true
>>
>>
>> If my understandings of the C99 integer promotion, value preserving and sign preserving rules are correct, the result should be false however.
>> The rationale and the rules for the above expression do appear complex, however LLVM and GCC both agree on me ;)
>>
>>
>> Here is code that corresponds to the expression above:
>>
>> uint8_t c = 0;
>> bool result = (c - 0xC2) < 0x32;
>>
>> LLVM and GCC will evaluate this to false.
>>
>>
>>
>> Regards
>> Andreas
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