Re: graceful unwind termination when we'd need unavailable/uncollect memory or registers to unwind further

[Pedro Alves <pedro@codesourcery.com>]

On Monday 28 February 2011 15:41:32, Jan Kratochvil wrote:
> In my case:
> 
> (gdb) tfind 0
> Found trace frame 0, tracepoint 2
> #0  f () at 1.c:11
> 11          v++;
> (gdb) bt
> #0  f () at 1.c:11
> Backtrace stopped: Not enough registers or memory available to unwind further
> (gdb) 
> 
> That is without that <unavailable>.  I think it is a bug.

That's expected.  In my example, the _PC_ was not
unwoundable in the outermost unwindable frame, but other
registers were.  In your example, it was, and I'm going
to guess that since you haven't collected any registers,
you're seeing the dwarf unwinder not being able to compute
the CFA.

In my example, notice info registers in the outermost
frame:

(gdb) bt
#0  begin () at ../../../src/gdb/testsuite/gdb.trace/unavailable.cc:180
#1  0x0000000000400b69 in main (argc=1, argv=0x7fffa180ace8, envp=0x7fffa180acf8) at ../../../src/gdb/testsuite/gdb.trace/unavailable.cc:329
#2  <unavailable> in ?? ()
Backtrace stopped: Not enough registers or memory available to unwind further
(gdb) up
#1  0x0000000000400b69 in main (argc=1, argv=0x7fffa180ace8, envp=0x7fffa180acf8) at ../../../src/gdb/testsuite/gdb.trace/unavailable.cc:329
329       begin ();
(gdb) 
#2  <unavailable> in ?? ()
(gdb) info registers 
rax            0x7fa45460eec8   140343767002824
rbx            0x0      0
rcx            0x5      5
rdx            0x7fffa180acf8   140735902952696
rsi            0x7fffa180ace8   140735902952680
rdi            0x1      1
rbp            *value not available*
rsp            0x7fffa180ac10   0x7fffa180ac10
r8             0x7fa45460d300   140343766995712
r9             0x7fa454dc05c0   140343775069632
r10            0x7fffa180a8f0   140735902951664
r11            0x7fa4542c8770   140343763568496
r12            0x4006b0 4196016
r13            0x7fffa180ace0   140735902952672
r14            0x0      0
r15            0x0      0
rip            *value not available*
eflags         0x203    [ CF IF ]
cs             0x33     51
ss             0x2b     43
ds             0x0      0
es             0x0      0
fs             0x0      0
gs             0x0      0

-- 
Pedro Alves