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Re: Anyone using efficient algorithm or HW support for NEXT/STEP?
- From: Andrew Cagney <ac131313 at redhat dot com>
- To: Wendy Peikes <wendyp at cisco dot com>
- Cc: gdb <gdb at sources dot redhat dot com>
- Date: Fri, 27 Sep 2002 20:44:48 -0400
- Subject: Re: Anyone using efficient algorithm or HW support for NEXT/STEP?
- References: <3D94C824.62A5113B@cisco.com>
Some thoughts:
- The latest GDB supports ``set trust-readonly-sections'' on. Which
stops GDB going to the target for prologe analysis. This is a big win.
- enhance the ``T'' packet to return registers such as PC, FP, ARG0, ...
that can help avoid the need for GDB to fetch all registers
- investigate a thread aware step-out-of-range packet.
Andrew
Here at Cisco, we've gotten both the host (started with gnu gdb 5.0)
and target gdb working for arm-elf.
(Note: I'd be glad to answer any questions about the arm gdb host
side and help with target-side questions)
We're (my target-side colleague and myself) are wondering if someone
is using a better algorithm for the NEXT and STEP commands:
Our gdb's single stepping is very slow. Current implementation (A)
(Note: applies, in general, to all platforms, not just to arm):
1- restore user installed breakpoints
2- command to single step.
3- ack and set temp breakpoint(s).
For arm, sets two temp breakpoints on branches and function calls;
one at the destination and one at next instruction. These cover
conditional execution either way it may go.
4- exception signal
5- remove breakpoints
6- collect regs to see where we are.
7- if still between start addr and stop addr, repeat,
if == stop addr: stop
8 - if in another function, determine return addr and
set breakpoint there
9 - continue
10 - go to 4
When it could be more efficient, simpler, and more robust to do B:
1- restore user installed breakpoints
2- set a temp breakpoint at stop addr
3 - continue
4- exception signal
5- collect regs and display where we are
Is anyone out there using a more efficient algorithm similar to B?
Also, is anyone using hardware single-stepping or hardware-assisted
stepping? For which platforms?
Thank you much for your help,
Wendy Peikes
Cisco Systems
Software Tools Group
GDB Support