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ptrace.2: Document the behavior of PTRACE_SYSEMU stops 

Signed-off-by: Keno Fischer <keno@juliacomputing.com>
This commit is contained in:
Keno Fischer 2016-11-16 00:51:59 -05:00 committed by Michael Kerrisk
parent 2b44a16879
commit 131bcd7aaa
1 changed files with 24 additions and 8 deletions
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32
man2/ptrace.2
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@ -737,7 +737,7 @@ is ignored.)
For
.BR PTRACE_SYSEMU ,
continue and stop on entry to the next system call,
which will not be executed.
which will not be executed. See the documentation on syscall-stops below.
For
.BR PTRACE_SYSEMU_SINGLESTEP ,
do the same but also singlestep if not a system call.
@ -1568,18 +1568,35 @@ set to
.IR "(event<<8)\ |\ SIGTRAP" .
.SS Syscall-stops
If the tracee was restarted by
.BR PTRACE_SYSCALL ,
.BR PTRACE_SYSCALL
or
.BR PTRACE_SYSEMU ,
the tracee enters
syscall-enter-stop just prior to entering any system call.
If the tracer restarts the tracee with
syscall-enter-stop just prior to entering any system call (which
will not be executed if the restart was using
.BR PTRACE_SYSEMU,
regardless of any change made to registers at this point or how the
tracee is restarted after this stop).
No matter which method caused the syscall-entry-stop,
if the tracer restarts the tracee with
.BR PTRACE_SYSCALL ,
the tracee enters syscall-exit-stop when the system call is finished,
or if it is interrupted by a signal.
(That is, signal-delivery-stop never happens between syscall-enter-stop
and syscall-exit-stop; it happens
.I after
syscall-exit-stop.)
syscall-exit-stop.). If the tracee is continued using any other method
(
including
.BR PTRACE_SYSEMU
), no syscall-exit-stop occurs. Note that all mentions
.BR PTRACE_SYSEMU
apply equally to
.BR PTRACE_SYSEMU_SINGLESTEP.
.LP
However, even if the tracee is was continued using
.BR PTRACE_SYSCALL
, it is not guaranteed that the next stop will be a syscall-exit-stop.
Other possibilities are that the tracee may stop in a
.B PTRACE_EVENT
stop, exit (if it entered
@ -1695,12 +1712,11 @@ set to
.B SIGTRAP
or
.IR (SIGTRAP|0x80) .
.SS PTRACE_SINGLESTEP, PTRACE_SYSEMU, PTRACE_SYSEMU_SINGLESTEP stops
.SS PTRACE_SINGLESTEP stops
[Details of these kinds of stops are yet to be documented.]
.\"
.\" FIXME .
.\" document stops occurring with PTRACE_SINGLESTEP, PTRACE_SYSEMU,
.\" PTRACE_SYSEMU_SINGLESTEP
.\" document stops occurring with PTRACE_SINGLESTEP
.SS Informational and restarting ptrace commands
Most ptrace commands (all except
.BR PTRACE_ATTACH ,