From 31ba933ec6a14b1f7fdbd9ba51f759e2c0537b9d Mon Sep 17 00:00:00 2001 From: Pedro Alves Date: Fri, 10 Jan 2020 20:05:52 +0000 Subject: [PATCH] Tweak handling of remote errors in response to resumption packet With current master, on a Fedora 27 machine with a kernel with buggy watchpoint support, I see: (gdb) PASS: gdb.threads/watchpoint-fork.exp: parent: singlethreaded: hardware breakpoints work continue Continuing. warning: Remote failure reply: E01 Remote communication error. Target disconnected.: Connection reset by peer. (gdb) FAIL: gdb.threads/watchpoint-fork.exp: parent: singlethreaded: watchpoints work continue The program is not being run. (gdb) FAIL: gdb.threads/watchpoint-fork.exp: parent: singlethreaded: breakpoint after the first fork (the program is no longer running) The FAILs themselves aren't what's interesting here. What is interesting is that with the main multi-target patch applied, I was getting this: (gdb) PASS: gdb.threads/watchpoint-fork.exp: parent: singlethreaded: hardware breakpoints work continue Continuing. warning: Remote failure reply: E01 /home/pedro/brno/pedro/gdb/binutils-gdb-2/build/../src/gdb/inferior.c:285: internal-error: inferior* find_inferior_pid(process_stratum_target*, int): Assertion `pid != 0' failed. A problem internal to GDB has been detected, further debugging may prove unreliable. Quit this debugging session? (y or n) FAIL: gdb.threads/watchpoint-fork.exp: parent: singlethreaded: watchpoints work (GDB internal error) The problem is that in remote_target::wait_as, we're hitting this: switch (buf[0]) { case 'E': /* Error of some sort. */ /* We're out of sync with the target now. Did it continue or not? Not is more likely, so report a stop. */ rs->waiting_for_stop_reply = 0; warning (_("Remote failure reply: %s"), buf); status->kind = TARGET_WAITKIND_STOPPED; status->value.sig = GDB_SIGNAL_0; break; which leaves event_ptid as null_ptid. At the end of the function, we then reach: else if (status->kind != TARGET_WAITKIND_EXITED && status->kind != TARGET_WAITKIND_SIGNALLED) { if (event_ptid != null_ptid) record_currthread (rs, event_ptid); else event_ptid = inferior_ptid; <<<<< here } and the trouble is that with the multi-target patch, we'll get here with inferior_ptid as null_ptid too. That is done exactly to find these implicit assumptions that inferior_ptid is a good choice for default thread, which isn't generaly true. I first thought of fixing this in the "case 'E'" path, but, given that this "event_ptid = inferior_ptid" path is also taken when the remote target does not support threads at all, no thread-related packets or extensions, it's better to fix it in latter path, to handle all scenarios that miss reporting a thread. That's what this patch does. gdb/ChangeLog: 2020-01-10 Pedro Alves * remote.c (first_remote_resumed_thread): New. (remote_target::wait_as): Use it as default event_ptid instead of inferior_ptid. --- gdb/ChangeLog | 6 ++++++ gdb/remote.c | 13 ++++++++++++- 2 files changed, 18 insertions(+), 1 deletion(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index fb7b93f6eee..9d63febea0f 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,9 @@ +2020-01-10 Pedro Alves + + * remote.c (first_remote_resumed_thread): New. + (remote_target::wait_as): Use it as default event_ptid instead of + inferior_ptid. + 2020-01-10 Pedro Alves * infrun.c (handle_no_resumed): Use all_non_exited_inferiors. diff --git a/gdb/remote.c b/gdb/remote.c index 51fa5da0c18..fa940dff720 100644 --- a/gdb/remote.c +++ b/gdb/remote.c @@ -7692,6 +7692,17 @@ remote_target::wait_ns (ptid_t ptid, struct target_waitstatus *status, int optio } } +/* Return the first resumed thread. */ + +static ptid_t +first_remote_resumed_thread () +{ + for (thread_info *tp : all_non_exited_threads (minus_one_ptid)) + if (tp->resumed) + return tp->ptid; + return null_ptid; +} + /* Wait until the remote machine stops, then return, storing status in STATUS just as `wait' would. */ @@ -7828,7 +7839,7 @@ remote_target::wait_as (ptid_t ptid, target_waitstatus *status, int options) if (event_ptid != null_ptid) record_currthread (rs, event_ptid); else - event_ptid = inferior_ptid; + event_ptid = first_remote_resumed_thread (); } else /* A process exit. Invalidate our notion of current thread. */ -- 2.30.2