segfault in sysdep/i386/backtrace.h

Mon Feb 19 18:06:00 GMT 2007

Marco Trudel wrote:
> Andrew Haley wrote:
>> Marco Trudel writes:
>> > > > The segfault happens on reading scan_bytes[x]. I assume that 
>> there is no > "pushl %ebp; movl %esp, %ebp" function prologue in 
>> certain cases and > thus we go reading protected areas below the 
>> function.
>>>> Why don't you have a look, and tell us what is there?
>> Because I don't know how and what these hex values mean (how to 
> interpret them) when doing the backtrace...

Ok, learnt it...
The problem is that the code assumes that there is always a "pushl %ebp; 
movl %esp, %ebp" function prologue. But, from [1]: "Note that many 
compilers can optimize these standard sequences away when not needed 
(often called "no stackframe generation")".
So, when turning on maximum optimization in microsoft visual c++, there 
are no longer "pushl %ebp; movl %esp, %ebp" intros and thus we run into 
trouble (tried it). I don't know if GCC can do that too... Can it?
I checked a couple of dll's (awt.dll, swt.dll, aBluetoothLib.dll) I had 
around and they all miss the intro in at least a couple of functions.
So, questions:
- Is this a sjlj-exception only problem? Can DW EH do that better?
- Is there another way to reliably recognize the start of a function? I 
assume this only affects native libs since Java compiled apps will 
always have the intro?!
Marco
[1] 
http://en.wikipedia.org/wiki/X86_calling_conventions#Standard_Exit_and_Entry_Sequences_for_C_Code