From e390720bdc6ddee752992537259d18d1ae8d2eb1 Mon Sep 17 00:00:00 2001 From: Yao Qi Date: Thu, 7 Apr 2016 16:47:26 +0100 Subject: [PATCH] Make breakpoint handling in record-full idempotent Some test fails in gdb.reverse/break-reverse.exp on arm-linux lead me seeing the following error message, continue^M Continuing.^M Cannot remove breakpoints because program is no longer writable.^M ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Further execution is probably impossible.^M ^M Breakpoint 3, bar () at /home/yao/SourceCode/gnu/gdb/git/gdb/testsuite/gdb.reverse/break-reverse.c:22^M 22 xyz = 2; /* break in bar */^M (gdb) PASS: gdb.reverse/break-reverse.exp: continue to breakpoint: bar backward this is caused by two entries in record_full_breakpoints, and their addr is the same, but in_target_beneath is different. during the record, we do continue, Continuing. infrun: clear_proceed_status_thread (Thread 13772.13772) infrun: proceed (addr=0xffffffff, signal=GDB_SIGNAL_DEFAULT) infrun: step-over queue now empty infrun: resuming [Thread 13772.13772] for step-over infrun: skipping breakpoint: stepping past insn at: 0x8620 Sending packet: $Z0,85f4,4#1d...Packet received: OK <---- ..... Sending packet: $vCont;c#a8...infrun: target_wait (-1.0.0, status) = infrun: -1.0.0 [process -1], infrun: status->kind = ignore infrun: TARGET_WAITKIND_IGNORE infrun: prepare_to_wait infrun: target_wait (-1.0.0, status) = infrun: -1.0.0 [process -1], infrun: status->kind = ignore infrun: TARGET_WAITKIND_IGNORE infrun: prepare_to_wait Packet received: T05swbreak:;0b:9cf5ffbe;0d:9cf5ffbe;0f:f4850000;thread:p35cc.35cc;core:1; Sending packet: $Z0,85f4,4#1d...Packet received: OK <----- .... Sending packet: $z0,85f4,4#3d...Packet received: OK <----- we can see breakpoint on 0x85f4 are inserted *twice*, but only removed once. That is fine to remote target, because Z/z packets are idempotent, but there is a leftover in record_full_breakpoints in record-full target. The flow can be described as below, record_full_breakpoints remote target ----------------------------------------------------------------------- forward execution, continue, in_target_beneath 1 breakpoint inserted insert breakpoints on 0x85f4 in_target_beneath 1 twice program stops, remove breakpoint on 0x85f4 in_target_beneath 1 breakpoint removed reverse execution, continue, in_target_beneath 1 none is requested insert breakpoints on 0x85f4, in_target_beneath 0 program stops, remote breakpoint on 0x85f4, in_target_beneath 0 request to remove, but GDBserver doesn't know now, the question is why breakoint on 0x85f4 is inserted twice? One is the normal breakpoint, and the other is the single step breakpoint. GDB inserts single step breakpoint to do single step. When program stops at 0x85f4, both of them are set on 0x85f4, and GDB deletes single step breakpoint, so in update_global_location_list, this breakpoint location is no longer found, GDB call force_breakpoint_reinsertion to mark it condition_updated, and insert it again. The reason force_breakpoint_reinsertion is called to update the conditions in the target side, because the conditions may be changed. My original fix is to not call force_breakpoint_reinsertion if OLD_LOC->cond is NULL, but it is not correct if another location on the same address has condition, GDB doesn't produce condition for target side, but GDB should do. Then, I change my mind back to make record-full handling breakpoint idempotent, to align with remote target. Before insert a new entry into record_full_breakpoints, look for existing one on the same address first. I also add an assert on "bp->in_target_beneath == in_target_beneath", to be safer. gdb: 2016-04-07 Yao Qi * record-full.c (record_full_insert_breakpoint): Return early if entry on the address is found in record_full_breakpoints. --- gdb/ChangeLog | 6 ++++++ gdb/record-full.c | 17 +++++++++++++++++ 2 files changed, 23 insertions(+) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 39f77f8844a..dfd49b9eada 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,9 @@ +2016-04-07 Yao Qi + + * record-full.c (record_full_insert_breakpoint): Return + early if entry on the address is found in + record_full_breakpoints. + 2016-04-07 Yao Qi * record-full.c (record_full_insert_breakpoint): Set diff --git a/gdb/record-full.c b/gdb/record-full.c index 066a8e73b35..d8aa89c8727 100644 --- a/gdb/record-full.c +++ b/gdb/record-full.c @@ -1650,6 +1650,7 @@ record_full_insert_breakpoint (struct target_ops *ops, { struct record_full_breakpoint *bp; int in_target_beneath = 0; + int ix; if (!RECORD_FULL_IS_REPLAY) { @@ -1681,6 +1682,22 @@ record_full_insert_breakpoint (struct target_ops *ops, bp_tgt->placed_size = bplen; } + /* Use the existing entries if found in order to avoid duplication + in record_full_breakpoints. */ + + for (ix = 0; + VEC_iterate (record_full_breakpoint_p, + record_full_breakpoints, ix, bp); + ++ix) + { + if (bp->addr == bp_tgt->placed_address + && bp->address_space == bp_tgt->placed_address_space) + { + gdb_assert (bp->in_target_beneath == in_target_beneath); + return 0; + } + } + bp = XNEW (struct record_full_breakpoint); bp->addr = bp_tgt->placed_address; bp->address_space = bp_tgt->placed_address_space; -- 2.30.2