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Re: segfault in sysdep/i386/backtrace.h
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