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Date: Sun, 24 Oct 2021 01:12:34 +0300
From: Konstantin Belousov <kostikbel@gmail.com>
To: Edward Tomasz Napierala <trasz@freebsd.org>
Cc: src-committers@freebsd.org, dev-commits-src-all@freebsd.org,
dev-commits-src-main@freebsd.org
Subject: Re: git: 6e66030c4c05 - main - linux: implement PTRACE_EVENT_EXEC
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On Sat, Oct 23, 2021 at 06:46:34PM +0000, Edward Tomasz Napierala wrote:
> The branch main has been updated by trasz:
>
> URL: https://cgit.FreeBSD.org/src/commit/?id=6e66030c4c05331f9b0adf87c31f2f233dd3ae1f
>
> commit 6e66030c4c05331f9b0adf87c31f2f233dd3ae1f
> Author: Edward Tomasz Napierala <trasz@FreeBSD.org>
> AuthorDate: 2021-10-23 18:13:14 +0000
> Commit: Edward Tomasz Napierala <trasz@FreeBSD.org>
> CommitDate: 2021-10-23 18:46:26 +0000
>
> linux: implement PTRACE_EVENT_EXEC
>
> This fixes strace(1) from Ubuntu Focal.
>
> Reviewed By: jhb
> Sponsored By: EPSRC
> Differential Revision: https://reviews.freebsd.org/D32367
> ---
> sys/amd64/linux/linux_ptrace.c | 9 +++++++--
> sys/kern/subr_syscall.c | 12 ++++++++++++
> 2 files changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/sys/amd64/linux/linux_ptrace.c b/sys/amd64/linux/linux_ptrace.c
> index 37f136856ef0..d7dffc92dd11 100644
> --- a/sys/amd64/linux/linux_ptrace.c
> +++ b/sys/amd64/linux/linux_ptrace.c
> @@ -71,6 +71,7 @@ __FBSDID("$FreeBSD$");
> #define LINUX_PTRACE_SEIZE 0x4206
> #define LINUX_PTRACE_GET_SYSCALL_INFO 0x420e
>
> +#define LINUX_PTRACE_EVENT_EXEC 4
> #define LINUX_PTRACE_EVENT_EXIT 6
>
> #define LINUX_PTRACE_O_TRACESYSGOOD 1
> @@ -151,8 +152,12 @@ linux_ptrace_status(struct thread *td, pid_t pid, int status)
> lwpinfo.pl_flags & PL_FLAG_SCE)
> status |= (LINUX_SIGTRAP | 0x80) << 8;
> if ((pem->ptrace_flags & LINUX_PTRACE_O_TRACESYSGOOD) &&
> - lwpinfo.pl_flags & PL_FLAG_SCX)
> - status |= (LINUX_SIGTRAP | 0x80) << 8;
> + lwpinfo.pl_flags & PL_FLAG_SCX) {
> + if (lwpinfo.pl_flags & PL_FLAG_EXEC)
> + status |= (LINUX_SIGTRAP | LINUX_PTRACE_EVENT_EXEC << 8) << 8;
> + else
> + status |= (LINUX_SIGTRAP | 0x80) << 8;
> + }
> if ((pem->ptrace_flags & LINUX_PTRACE_O_TRACEEXIT) &&
> lwpinfo.pl_flags & PL_FLAG_EXITED)
> status |= (LINUX_SIGTRAP | LINUX_PTRACE_EVENT_EXIT << 8) << 8;
> diff --git a/sys/kern/subr_syscall.c b/sys/kern/subr_syscall.c
> index ada2053bc87c..fab67a68b0a3 100644
> --- a/sys/kern/subr_syscall.c
> +++ b/sys/kern/subr_syscall.c
> @@ -254,6 +254,18 @@ syscallret(struct thread *td)
> if (__predict_false(traced ||
> (td->td_dbgflags & (TDB_EXEC | TDB_FORK)) != 0)) {
> PROC_LOCK(p);
> + /*
> + * Linux debuggers expect an additional stop for exec,
> + * between the usual syscall entry and exit. Raise
> + * the exec event now and then clear TDB_EXEC so that
> + * the next stop is reported as a syscall exit by
> + * linux_ptrace_status().
> + */
> + if ((td->td_dbgflags & TDB_EXEC) != 0 &&
> + SV_PROC_ABI(td->td_proc) == SV_ABI_LINUX) {
> + ptracestop(td, SIGTRAP, NULL);
> + td->td_dbgflags &= ~TDB_EXEC;
> + }
> /*
> * If tracing the execed process, trap to the debugger
> * so that breakpoints can be set before the program
You committed before we finished the discussion.
In fact I do not think it is right. Now it generates spurious stop for
FreeBSD native debugger, and probably de-synchronize SCX/SCE pairing for
it as well.
In other words, you need to generate this stop based on ABI of the debugger,
not debuggeeeeee.