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Wed, 22 Nov 2023 16:16:48 +0000 (UTC) (envelope-from jhb@FreeBSD.org) Message-ID: Date: Wed, 22 Nov 2023 08:16:46 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] [gdb/tdep] Add syscall number cache Content-Language: en-US To: Tom de Vries , gdb-patches@sourceware.org References: <20231122091020.8640-1-tdevries@suse.de> From: John Baldwin In-Reply-To: <20231122091020.8640-1-tdevries@suse.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-11.8 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,SPF_HELO_NONE,SPF_PASS,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On 11/22/23 1:10 AM, Tom de Vries wrote: > When running test-case gdb.base/catch-syscall.exp on powerpc64le-linux, we run > into an xfail: > ... > (gdb) catch syscall execve^M > Catchpoint 18 (syscall 'execve' [11])^M > (gdb) PASS: gdb.base/catch-syscall.exp: execve: \ > catch syscall with arguments (execve) > ... > continue^M > Continuing.^M > ^M > Catchpoint 18 (call to syscall execve), 0x00007ffff7d7f18c in execve () from \ > /lib64/libc.so.6^M > (gdb) PASS: gdb.base/catch-syscall.exp: execve: program has called execve > continue^M > Continuing.^M > process 60484 is executing new program: catch-syscall^M > ^M > Breakpoint 17, main (argc=1, argv=0x7fffffffe618) at catch-syscall.c:54^M > 54 char buf1[2] = "a";^M > (gdb) XFAIL: gdb.base/catch-syscall.exp: execve: syscall execve has returned > ... > > The problem is that the catchpoint "(return from syscall execve)" doesn't > trigger. > > This is caused by ppc_linux_get_syscall_number returning 0 at execve > syscall-exit-stop, while it should return 11. > > This is a problem that was fixed in linux kernel version v5.19, by commit > ec6d0dde71d7 ("powerpc: Enable execve syscall exit tracepoint"), but the > machine I'm running the tests on has v4.18.0. > > An approach was discussed in the PR where ppc_linux_get_syscall_number would > try to detect an execve syscall-exit-stop based on the register state, but > that was considered too fragile. > > Fix this by caching the syscall number at syscall-enter-stop, and reusing it > at syscall-exit-stop. > > This is sufficient to stop triggering the xfail, so remove it. > > It's good to point out that this doesn't always eliminate the need to get the > syscall number at a syscall-exit-stop. > > The test-case has an example called mid-vfork, where we do: > - catch vfork > - continue > - catch syscall > - continue. > > The following things happen: > - the "catch vfork" specifies that we capture the PTRACE_EVENT_VFORK event. > - the first continue runs into the event > - the "catch syscall" specifies that we capture syscall-enter-stop and > syscall-exit-stop events. > - the second continue runs into the syscall-exit-stop. At that point there's > no syscall number value cached, because no corresponding syscall-enter-stop > was observed. > > We can address this issue somewhat by translating events into syscalls. A > followup patch in this series use this approach (though not for vfork). > > PR tdep/28623 > Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28623 > --- > gdb/linux-nat.c | 45 ++++++++++++++++++++++-- > gdb/linux-nat.h | 3 ++ > gdb/testsuite/gdb.base/catch-syscall.exp | 8 +---- > 3 files changed, 46 insertions(+), 10 deletions(-) > > diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c > index 7b0562cf89b..ab6eadd557d 100644 > --- a/gdb/linux-nat.c > +++ b/gdb/linux-nat.c > @@ -1508,6 +1508,17 @@ linux_resume_one_lwp_throw (struct lwp_info *lp, int step, > else > lp->stop_pc = 0; > > + if (catch_syscall_enabled () > 0) > + { > + /* Function inf_ptrace_target::resume uses PT_SYSCALL. */ > + } > + else > + { > + /* Function inf_ptrace_target::resume uses PT_CONTINUE. > + Invalidate syscall_number cache. */ > + lp->syscall_number = -1; > + } > + > linux_target->low_prepare_to_resume (lp); > linux_target->low_resume (lp->ptid, step, signo); > > @@ -1762,7 +1773,26 @@ linux_handle_syscall_trap (struct lwp_info *lp, int stopping) > struct target_waitstatus *ourstatus = &lp->waitstatus; > struct gdbarch *gdbarch = target_thread_architecture (lp->ptid); > thread_info *thread = linux_target->find_thread (lp->ptid); > + > + enum target_waitkind new_syscall_state > + = (lp->syscall_state == TARGET_WAITKIND_SYSCALL_ENTRY > + ? TARGET_WAITKIND_SYSCALL_RETURN > + : TARGET_WAITKIND_SYSCALL_ENTRY); > + > int syscall_number = (int) gdbarch_get_syscall_number (gdbarch, thread); > + if (new_syscall_state == TARGET_WAITKIND_SYSCALL_RETURN > + && lp->syscall_number != -1 > + && lp->syscall_number != syscall_number) > + { > + /* Calling gdbarch_get_syscall_number for TARGET_WAITKIND_SYSCALL_RETURN > + is unreliable on some targets for some syscalls, use the syscall > + detected at TARGET_WAITKIND_SYSCALL_ENTRY instead. */ > + linux_nat_debug_printf > + (_("Using syscall number %d supplied by syscall_number cache instead" > + " of %d supplied by architecture hook"), > + lp->syscall_number, syscall_number); > + syscall_number = lp->syscall_number; > + } > > if (stopping) > { > @@ -1801,9 +1831,18 @@ linux_handle_syscall_trap (struct lwp_info *lp, int stopping) > the user could install a new catchpoint for this syscall > between syscall enter/return, and we'll need to know to > report a syscall return if that happens. */ > - lp->syscall_state = (lp->syscall_state == TARGET_WAITKIND_SYSCALL_ENTRY > - ? TARGET_WAITKIND_SYSCALL_RETURN > - : TARGET_WAITKIND_SYSCALL_ENTRY); > + lp->syscall_state = new_syscall_state; > + > + if (lp->syscall_state == TARGET_WAITKIND_SYSCALL_ENTRY) > + { > + /* Save to use in TARGET_WAITKIND_SYSCALL_RETURN. */ > + lp->syscall_number = syscall_number; > + } > + else > + { > + /* Reset to prevent stale values. */ > + lp->syscall_number = -1; > + } > > if (catch_syscall_enabled ()) > { > diff --git a/gdb/linux-nat.h b/gdb/linux-nat.h > index 428bb9f1628..b17037400a3 100644 > --- a/gdb/linux-nat.h > +++ b/gdb/linux-nat.h > @@ -277,6 +277,9 @@ struct lwp_info : intrusive_list_node > - TARGET_WAITKIND_SYSCALL_RETURN */ > enum target_waitkind syscall_state; > > + /* Syscall number corresponding to syscall_state. */ > + int syscall_number = -1; > + > /* The processor core this LWP was last seen on. */ > int core = -1; > > diff --git a/gdb/testsuite/gdb.base/catch-syscall.exp b/gdb/testsuite/gdb.base/catch-syscall.exp > index 0588cb35d87..d8ea466cf00 100644 > --- a/gdb/testsuite/gdb.base/catch-syscall.exp > +++ b/gdb/testsuite/gdb.base/catch-syscall.exp > @@ -134,13 +134,7 @@ proc check_return_from_syscall { syscall { pattern "" } } { > return 1 > } > -re -wrap ".*Breakpoint $decimal, main .*" { > - # On Powerpc the kernel does not report the returned from > - # syscall as expected by the test. GDB bugzilla 28623. > - if { [istarget "powerpc64*-linux*"] } { > - xfail $thistest > - } else { > - fail $thistest > - } > + fail $thistest > return 0 > } > } > > base-commit: 790ce1f70c25129b35e060329cdf2915a6def9fd This looks good to me. -- John Baldwin