On Fri, 27 May 2011, Andrea Pellegrini wrote:
Hi all,
I heavily modified the O3 cpu to implement my own architecture and I am
still debugging it for some corner cases.
However, I am experiencing a really weird behavior in m5. When I debug m5 in
gdb (either with eclipse or kdbg) I see the outputs deviate from the
expected behavior.
The runs are consistent within running m5 in console and running it in gdb,
differing always in the same way. The two runs have *exactly* the same
arguments.
This is the command line I use (I added my own trace flags and some extra
parameters):
m5/build/X86_SE/m5.debug
--trace-flags=O3CPU,TLB,Fetch,Decode,Rename,IEW,IQ,Commit,ROB,Writeback,IntRegs,ROB,LSQUnit,TSU,TGCluster,TGFetch,TGDecode,TGRename,TGIEW,TGCommit,TGDATAFlow,TGCrossbar
/m5/configs/example/se_andrea.py -d --caches -n 1 -c
m5/tests/test-progs/hello/bin/x86/linux/hello --num_faults=0
========================================================================================================
This is what I get when I diff the log files:
10c10
< M5 started May 26 2011 23:26:49
---
M5 started May 26 2011 22:55:04
12c12
---
< 15479500: global: RegFile: Setting int register 249 to 0x7fffffffef4c
---
15479500: global: RegFile: Setting int register 249 to 0x7fffffffef4e
2164282,2164283c2164282,2164283
...
other differences from here
========================================================================================================
I have no idea why running in gdb should modify the behavior of the
simulation. I tried to valgrind m5 to check if I was using some initialized
variable or pointer, but everything seems fine.
I currently working on understanding what is wrong with it, and I was
wondering if somebody else already experienced this odd behavior.
Thanks!
-Andrea
Andrea, from my personal experience, I would say that gdb does not modify
the visible behavior unless there is some bug in the program. I would
expect that some memory access is going on wrongly some where. Try to
traceback from the point where you first spot the two executions
diverging.
--
Nilay
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