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[Bug gdb/19061] gdb-7.10 hangs/spins-on-cpu when debugging any program on Alpha
- From: "palves at redhat dot com" <sourceware-bugzilla at sourceware dot org>
- To: gdb-prs at sourceware dot org
- Date: Tue, 17 May 2016 16:41:25 +0000
- Subject: [Bug gdb/19061] gdb-7.10 hangs/spins-on-cpu when debugging any program on Alpha
- Auto-submitted: auto-generated
- References: <bug-19061-4717 at http dot sourceware dot org/bugzilla/>
https://sourceware.org/bugzilla/show_bug.cgi?id=19061
--- Comment #4 from Pedro Alves <palves at redhat dot com> ---
We see:
LLR: Preparing to step process 2636, 0, inferior_ptid process 2636
LLR: PTRACE_SINGLESTEP process 2636, 0 (resume event thread)
...
LLW: waitpid 2636 received Trace/breakpoint trap (stopped)
CSBB: process 2636 stopped by software breakpoint
...
infrun: stop_pc = 0x20000003428
infrun: delayed software breakpoint trap, ignoring
And Alpha is a decr_pc_after_break arch:
$ grep decr_pc_after * | grep alpha
alpha-tdep.c: set_gdbarch_decr_pc_after_break (gdbarch, ALPHA_INSN_SIZE);
If GDB got that "stopped by software breakpoint" stop reason wrong, it will
decrement the thread's PC by ALPHA_INSN_SIZE when it shouldn't. Then the next
time the thread is resumed, it executes the wrong instruction, in turn
manifesting in odd things like odd loops and crashes.
See linux-nat.c:save_stop_reason for where the PC is decremented.
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