From 677c92fe9a530f3f8959b8a0e311f58f9a616fa4 Mon Sep 17 00:00:00 2001 From: Simon Marchi Date: Mon, 14 Sep 2020 11:51:04 -0400 Subject: [PATCH] gdb: don't use inferior_ptid in linux_nat_wait_1 target_ops::wait implementations should not rely on the value of inferior_ptid on entry. While looking at another wait-related patch, I noticed that the code in linux_nat_wait_1, checking for a newly created process, did just that. This patch fixes it. Note that I didn't see any bug, this "fix" is simply to make the function respect the target_ops::wait contract. Instead of checking inferior_ptid, check for the passed in `ptid` value. During startup, linux_nat_wait_1 gets called a few times with the pid-only ptid, while startup_inferior waits for the expected number of exec events. For this reason, I needed to add a `find_lwp_pid` call to ensure that the actions of changing the main thread's ptid, and adding the initial lwp, were done only once for a given process. This was not needed before, since thread_change_ptid, through the thread_ptid_changed observer, ends up changing inferior_ptid. So the second time around, inferior_ptid was not a pid-only ptid. That find_lwp_pid won't add much overhead, as it will only be called when the ptid is a pid-only ptid. And AFAIK, that only happens during inferior startup. An alternative to that `find_lwp_pid` call might be to make startup_inferior realize that the main thread has changed ptid, and make it wait for the new ptid. But that doesn't look easy to do. Regtested on amd64/Linux. gdb/ChangeLog: * linux-nat.c (linux_nat_wait_1): Don't use inferior_ptid when checking for initial lwp. Change-Id: I8f1d5c766f5cb2a29c948bc75fa4582d7130c23f --- gdb/ChangeLog | 5 +++++ gdb/linux-nat.c | 11 +++++------ 2 files changed, 10 insertions(+), 6 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index dabc7266dba..c60d20b9a69 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,8 @@ +2020-09-14 Simon Marchi + + * linux-nat.c (linux_nat_wait_1): Don't use inferior_ptid when + checking for initial lwp. + 2020-09-14 Tom Tromey * m68k-tdep.c (m68k_extract_return_value): Use diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c index b81014024c7..4f53670da5e 100644 --- a/gdb/linux-nat.c +++ b/gdb/linux-nat.c @@ -3143,14 +3143,13 @@ linux_nat_wait_1 (ptid_t ptid, struct target_waitstatus *ourstatus, /* The first time we get here after starting a new inferior, we may not have added it to the LWP list yet - this is the earliest moment at which we know its PID. */ - if (inferior_ptid.is_pid ()) + if (ptid.is_pid () && find_lwp_pid (ptid) == nullptr) { - /* Upgrade the main thread's ptid. */ - thread_change_ptid (linux_target, inferior_ptid, - ptid_t (inferior_ptid.pid (), - inferior_ptid.pid (), 0)); + ptid_t lwp_ptid (ptid.pid (), ptid.pid ()); - lp = add_initial_lwp (inferior_ptid); + /* Upgrade the main thread's ptid. */ + thread_change_ptid (linux_target, ptid, lwp_ptid); + lp = add_initial_lwp (lwp_ptid); lp->resumed = 1; } -- 2.30.2