Re: [DynInst_API:] Variable size and frame pointers

[Bill Williams <bill@xxxxxxxxxxx>]

On 08/18/2014 03:39 AM, Fabian Mager wrote:
> Hello all,
>
> I have two questions. Therefore, I uploaded a small mutatee
> program(http://pastebin.com/1wsuSRmE) and the respective mutator program
> (http://pastebin.com/KyXUC9mm). The output is the following:
>
>  > clang -Wall -g -O0 struct.c -o struct
>  > clang++ -Wall -g -O0 -std=c++11 procapi.cpp -I... -L... -lpcontrol
> -lstackwalk -lsymtabAPI -o procapi
>  >./procapi
>
> stack from bottom to top:
>      foo    FP: 140736267700336    SP: 140736267700312
>      main    FP: 140736267700336    SP: 140736267700320
>      __libc_start_main    FP: 0    SP: 140736267700352
>      _start    FP: 0    SP: 140736267700544
>
> parameters:
>      s: s_t -- 8 Bytes
>       --> Setting size to 0
>      s: s_t -- 16 Bytes
>
> greetings from foo!
>
> Variable s of type struct s_t has a size of 16 Bytes on my system. I
> don't understand why getSize() returns 8 Bytes on the first attempt and
> after calling setSize(0), it returns the correct 16 Bytes. The sizes
> vary a bit when using gcc instead of clang but they are still not equal.
Patch below; let me know if it works.

> The second question focuses on the frame pointers (FP). foo and main
> have the same FP but that should not be the case and causes troubles
> when I later on try to get the actual parameter values with
> getLocalVariableValue(). I assume the reason for that is the way I set
> the breakpoint(process->addBreakpoint(f_foo->getOffset(), breakpoint)).
> How do I set the breakpoint to the beginning of the function call?
If you're trying to get parameter values, you need to do that inside an 
address range where the DWARF information we have for them is valid. 
That's generally going to be after stack frame setup, which is a few 
instructions into the function, for anything that's not passed in a 
register.
If you look at the variable locations of the parameters, they should 
have address ranges attached to them, and you should be able to set your 
breakpoint at the beginning of the valid range with no problem.
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--
--bw

Bill Williams
Paradyn Project
bill@xxxxxxxxxxx

diff --git a/symtabAPI/src/Type.C b/symtabAPI/src/Type.C
index 302a99d..a68f718 100644
--- a/symtabAPI/src/Type.C
+++ b/symtabAPI/src/Type.C
@@ -197,7 +197,8 @@ bool Type::operator==(const Type &otype) const

 unsigned int Type::getSize()
 {
-       if (!size_)
+  // If default constructed, update
+  if (!size_ || (size_ == sizeof(int)))
                const_cast<Type *>(this)->updateSize();
        return size_;
 }