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Remember that on SPARC (leon3), parts of the stack will be cached in
the register file windows. Printing the backtrace by following the
stack/frame pointers will then not work unless all windows are first
flushed to memory. This is done automatically on high-level O/S
(Linux & Solaris), but not on embedded systems like RTEMS.<br>
<br>
Jiri.<br>
<br>
On 07/12/16 13:30, Matthew J Fletcher wrote:<br>
<blockquote
cite="mid:CAPy9Tik5nHC1NvEBH1L9=cdE+mwBnEWkmtQiBB1v+R+jzzn_nA@mail.gmail.com"
type="cite">
<div dir="ltr">Hi,
<div><br>
</div>
<div>The gcc builtin functions (and libunwind) and only work if
the stack frame information is not optimised away, this is
controlled by gcc compiler flags, see; <a
moz-do-not-send="true"
href="https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html"><a class="moz-txt-link-freetext" href="https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html">https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html</a></a> <span
style="color:rgb(0,0,0);font-family:monospace;font-size:medium">-fomit-frame-pointer</span></div>
<div><span
style="color:rgb(0,0,0);font-family:monospace;font-size:medium"><br>
</span></div>
<div><span
style="color:rgb(0,0,0);font-family:monospace;font-size:medium">Without
that you have to do your own unwinding, for example on x86
you could do the following, but its pretty crude.
Linux/FreeBSD do much more fancy unwinders, it depends on
what you want.</span></div>
<div><span
style="color:rgb(0,0,0);font-family:monospace;font-size:medium"><br>
</span></div>
<div>
<div><font color="#000000" size="3" face="monospace">#define
get_ebp() \</font></div>
<div><font color="#000000" size="3" face="monospace">({
unsigned long __value; \</font></div>
<div><font color="#000000" size="3" face="monospace"> asm
volatile (" mov %%ebp,%0": "=a"(__value)); \</font></div>
<div><font color="#000000" size="3" face="monospace">
__value; })</font></div>
</div>
<div><font color="#000000" size="3" face="monospace"><br>
</font></div>
<div><font color="#000000" size="3" face="monospace">
<div>void error_dump_callstack(int fd)</div>
<div>{</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>unsigned
long<span class="gmail-Apple-tab-span" style="white-space:pre"> </span>ebp=0,arg0,arg4,arg8,arg12,arg16;</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>int
i;</div>
<div><br>
</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>arg0
= get_ebp(); // base pointer, start of current stack frame</div>
<div><br>
</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>assert_out(fd,"\r\nCall
Stack Information:\r\n\r\n");</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>for
(i=0; i<15; i++)</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>{</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>//
attempt get backtrace (with arguments) from stored EPB</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>arg0
= *(unsigned long*)(arg0);</div>
<div><br>
</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>if
(arg0 == 0)</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>break;</div>
<div><br>
</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>//
print stackframe back past inturrupt</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>arg0
= *(unsigned long*)(arg0);</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>arg4
= *(unsigned long*)(arg0+4);</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>arg8
= *(unsigned long*)(arg0+8);</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>arg12
= *(unsigned long*)(arg0+12);</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>arg16
= *(unsigned long*)(arg0+16);</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span></div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>sprintf(assertbuffer,"ebp:
%p\r\nframe%d: %p\r\narg1: %p\r\narg2:
%p\r\narg3: %p\r\n",arg0,i,arg4,arg8,arg12,arg16);</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>assert_out(fd,assertbuffer);</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>}</div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span></div>
<div><span class="gmail-Apple-tab-span" style="white-space:pre"> </span>assert_out(fd,"use
'addr2line -C -e abc.elf -f address' to get symbol
names\r\n");</div>
<div>}</div>
<div><br>
</div>
<div><br>
</div>
</font></div>
<div><span
style="color:rgb(0,0,0);font-family:monospace;font-size:medium"><br>
</span></div>
<div><span
style="color:rgb(0,0,0);font-family:monospace;font-size:medium"><br>
</span></div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On 6 December 2016 at 22:36, Chris
Johns <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:chrisj@rtems.org" target="_blank">chrisj@rtems.org</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">On
06/12/2016 01:46, Jan Sommer wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
Is there a common way how to create stacktraces in RTEMS?<br>
</blockquote>
<br>
Not that I know of.<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
I tried to use the _Unwind_Backtrace_-function from gcc,
but so far it<br>
only returns _URC_END_OF_STACK if I call it from a leaf
function<br>
(haven't tried a trap handler yet).<br>
</blockquote>
<br>
The end of stack code means the unwinder could not find any
data about the frames in the stack. The default DWARF
unwinder, which SPARC uses, searches for a valid Frame
Description Entry (FDE) and if not found reports the end of
stack code. If an FDE is found the Common Information Entry
(CIE) is extracted from that data and the frame info
decoded.<br>
<br>
C++ uses the same process for exceptions. A .eh_frame plus
some other sections are created and the frames effected by
the exceptions added to these sections. These sections are
registered at start up. For a DWARF unwinder, which includes
the SPARC, the DWARF standard is used for the format of
these sections.<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
I am not sure if that is the way to go.<br>
</blockquote>
<br>
I am not 100% sure myself. I think you would need to include
some level of DWARF related information in the executable to
do this. This information would need to be registered with
the DWARF unwinder code via something like 'void
__register_frame (void *begin)'.<br>
<br>
I would also take a look at FreeBSD and see how they
implement the unwinder. I do not know if the FreeBSD kernel
has one.<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
Are there any recommendations or examples for this topic?<br>
</blockquote>
<br>
The DWARF standard website is the best source of info:<br>
<br>
<a moz-do-not-send="true" href="http://dwarfstd.org/"
rel="noreferrer" target="_blank">http://dwarfstd.org/</a><br>
<br>
Chris<br>
<br>
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</blockquote>
</div>
<br>
<br clear="all">
<div><br>
</div>
-- <br>
<div class="gmail_signature" data-smartmail="gmail_signature">
<div><br>
regards</div>
<div>---</div>
<div>Matthew J Fletcher</div>
<br>
</div>
</div>
<br>
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