Re: huge remote debug traffic with multi-thread program

[Atsushi Nemoto <anemo@mba.ocn.ne.jp>]

>>>>> On Thu, 17 Feb 2005 10:42:00 +0900 (JST), Atsushi Nemoto <anemo@mba.ocn.ne.jp> said:
anemo> Looking the log, gdbserver keep getting SIGTRAP on 0x00404a78
anemo> (__pthread_wait_for_restart_signal+132).  This is a return
anemo> address from __pthread_sigsuspend() which is a stopping place
anemo> of SIGINT (Ctrl-C).  I'm wondering why gdb set breakpoint to
anemo> the return address of __pthread_sigsuspend() ...

The reason was gdb is doing software single-step on resuming.

The instruction on stop_pc is 'jr ra' in __pthread_sigsuspend.  When
resuming, gdb set breakpoint of the return address to do software
single-stop.

Next question is why gdb try to do single step here.  It seems due to
this code in infrun.c:proceed().

712:      else if (gdbarch_single_step_through_delay_p (current_gdbarch)
713:              && gdbarch_single_step_through_delay (current_gdbarch,
714:                                                    get_current_frame ()))
715:        /* We stepped onto an instruction that needs to be stepped
716:           again before re-inserting the breakpoint, do so.  */
717:        oneproc = 1;

On mips, gdbarch_single_step_through_delay return 1 for 'jr' instruction.

In gdb 6.3, it was:

732:      if (STEP_SKIPS_DELAY_P
732:          && breakpoint_here_p (read_pc () + 4)
732:          && STEP_SKIPS_DELAY (read_pc ()))
732:        oneproc = 1;

and ChangeLog saied:

2004-10-31  Orjan Friberg <organ.friberg@axis.com>
	    Andrew Cagney  <cagney@gnu.org>

	* gdbarch.sh (single_step_through_delay): Add.
	* gdbarch.h, gdbarch.c: Re-generate.
	* config/mips/tm-mips.h (STEP_SKIPS_DELAY_P, STEP_SKIPS_DELAY)
	(mips_step_skips_delay): Delete.
	* mips-tdep.c (mips_single_step_through_delay): Replace
	mips_step_skips_delay.
	(mips_gdbarch_init): Set single_step_through_delay.
	(mips_dump_tdep): Do not print STEP_SKIPS_DELAY.

It seems "breakpoint_here_p (read_pc() + 4)" test was lost.
Is this intentional?

Thank you.
---
Atsushi Nemoto