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Before this change:
$ strace -D -p1
strace: -D and -p are mutually exclusive options
Process 1 detached <==== WRONG! (and we try to SIGSTOP it!!!)
* defs.h: Change the meaning of TCB_ATTACHED: now it means "this tracee
is attached to us". Add TCB_STRACE_CHILD: "this tracee is our child".
* strace.c (kill_save_errno): Move up. No code changes.
(process_opt_p_list): Don't set TCB_ATTACHED on new tcb.
(startup_attach): Change how we work with TCB_ATTACHED.
Set TCB_STRACE_CHILD on -D.
(startup_child): Use kill_save_errno instead of kill.
Set TCB_ATTACHED and TCB_STRACE_CHILD on attached strace child.
If we are in -D case, don't set TCB_ATTACHED (we aren't attached yet).
(detach): do not do PTRACE_DETACH if TCB_ATTACHED is not set.
(cleanup): Check TCB_STRACE_CHILD instead of TCB_ATTACHED.
(trace): Likewise.
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
* defs.h: Clarify meaning of TCB_ATTACHED. No code changes.
* strace.c (process_opt_p_list): New function.
(main): Call process_opt_p_list to process -p PIDs argument.
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
While we are at it, fold do_ptrace into its lone caller.
We no longer set tcp->ptrace_errno = ESRCH on ESRC error in upeek.
Other code paths where ptrace fails wern't doing it, and the code which
checks tcp->ptrace_errno even assumes it is never set to ESRCH.
(It was me who added this code sometime ago, so it was my fault
that it was a bit messy)
I ran sigkill_rain test and verified that unfinished syscalls are
still handled correctly.
* util.c (ptrace_restart): Do not pass addr=1 to ptrace(), pass 0 instead.
I have no idea why we were passing 1. Ptrace documentation says
that addr parameter is ignored.
(do_ptrace): Remove this function.
(upeek): Use ptrace() instead of do_ptrace().
* defs.h: Remove do_ptrace() declaration.
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
text data bss dec hex filename
237384 672 19044 257100 3ec4c strace.before
236448 672 19044 256164 3e8a4 strace
* defs.h: Declare new functions printargs_lu(), printargs_ld()
which simply print syscall all args as unsigned or signed longs.
* desc.c (sys_epoll_create): Call printargs_ld() instead of open-coding it.
* linux/syscall.h: Remove declarations of the following functions:
sys_alarm, sys_getresgid, sys_getsid, sys_nice, sys_setgid, sys_setpgid,
sys_setpgrp, sys_setregid, sys_setresgid.
* process.c (sys_setgid): Delete this function: now aliased to sys_setuid().
(sys_getresgid): Delete this function: now aliased to sys_getresuid().
(sys_setregid): Delete this function: now aliased to sys_setreuid().
(sys_setresgid): Delete this function: now aliased to sys_setresuid().
(sys_setpgrp): Delete this function: now aliased to printargs_lu().
(sys_getsid): Likewise.
(sys_setpgid): Likewise.
(sys_alarm): Likewise.
(sys_getpgrp): Delete this function: was unused - was already shadowed
by a define in linux/dummy.h.
(sys_setsid): Likewise.
(sys_getpgid): Likewise.
* resource.c (sys_nice): Delete this function: now aliased to printargs_ld().
* linux/dummy.h: Define new aliases (see above for the list).
* syscall.c (printargs_lu): New function.
(printargs_ld): New function.
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This change is abapted from Dmitry's changes to remove support for
non-Linux architectures.
* Makefile.am: Remove if LINUX/endif pairs.
* defs.h: Remove stream_ioctl() declaration.
* ioctl.c (ioctl_decode): Remove 'ifdef HAVE_SYS_STREAM_H' block.
* resource.c: Use 'defined(FOO)' instead of 'defined FOO' form.
* util.c: Likewise.
* signal.c: Remove conditional includes which are never used on Linux.
* stream.c: Likewise.
* file.c: Remove excessive empty lines.
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Conditions such as defined(LINUX) are always true now,
defined(FREEBSD) etc are always false.
When if directive has them as subexpressions, it can be simplified.
Another trivial changes here are fixes for directive indentation.
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This change is generated by running every source through the following command:
unifdef -DLINUX -Dlinux -USUNOS4 -USVR4 -UUNIXWARE -UFREEBSD
-USUNOS4_KERNEL_ARCH_KLUDGE -UHAVE_MP_PROCFS
-UHAVE_POLLABLE_PROCFS -UHAVE_PR_SYSCALL -UUSE_PROCFS file.c
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
The native_scno field is not so much used in the code than before.
In many cases sys_func is checked instead, and for most of syscall
entries there is no need to initialize native_scno.
* linux/i386/syscallent.h: Remove native_scno initialization for
_exit, read, write, waitpid, execve, wait4, sysfs, readv, writev,
pread64, pwrite64, exit_group, waitid, send, recv, sendto and
recvfrom syscall entries.
* linux/syscall.h: Do not define no longer used SYS_waitid and
SYS_sub_* constants.
[IA64]: Do not define SYS_waitpid and SYS32_* constants.
* defs.h: Do not define no longer used __NR_exit_group constant.
* strace.c [USE_PROCFS] (proc_open): Use sys_func to check for execve.
Avoid NULL dereference when there are holes in sysent tables.
It can happen with syscall (number, ...) and number is in those holes.
There are no targets with holey systent tables so far, but at least
one such a target, x32, is already on the horizon.
* defs.h (SCNO_IN_RANGE): Also check the sys_func field.
All new code is predicated on "ifdef USE_SEIZE". If it is not defined,
behavior is not changed.
If USE_SEIZE is enabled and run-time check shows that PTRACE_SEIZE works, then:
- All attaching is done with PTRACE_SEIZE + PTRACE_INTERRUPT.
This means that we no longer generate (and possibly race with) SIGSTOP.
- PTRACE_EVENT_STOP will be generated if tracee is group-stopped.
When we detect it, we issue PTRACE_LISTEN instead of PTRACE_SYSCALL.
This leaves tracee stopped. This fixes the inability to SIGSTOP or ^Z
a straced process.
* defs.h: Add commented-out "define USE_SEIZE 1" and define PTRACE_SEIZE
and related constants.
* strace.c: New variable post_attach_sigstop shows whether we age going
to expect SIGSTOP on attach (IOW: are we going to use PTRACE_SEIZE).
(ptrace_attach_or_seize): New function. Uses PTRACE_ATTACH or
PTRACE_SEIZE + PTRACE_INTERRUPT to attach to given pid.
(startup_attach): Use ptrace_attach_or_seize() instead of ptrace(PTRACE_ATTACH).
(startup_child): Conditionally use alternative attach method using PTRACE_SEIZE.
(test_ptrace_setoptions_followfork): More robust parameters to PTRACE_TRACEME.
(test_ptrace_seize): New function to test whether PTRACE_SEIZE works.
(main): Call test_ptrace_seize() while initializing.
(trace): If PTRACE_EVENT_STOP is seen, restart using PTRACE_LISTEN in order
to not let tracee run.
* process.c: Decode PTRACE_SEIZE, PTRACE_INTERRUPT, PTRACE_LISTEN.
* util.c (ptrace_restart): Add "LISTEN" to a possible error message.
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
* defs.h: Rename tcp_last to printing_tcp. Explain what it means.
Remove printtrailer() function.
* process.c (sys_exit): Convert printtrailer() call to "printing_tcp = NULL".
* strace.c: Add new variable printing_tcp.
(cleanup): Convert printtrailer() call to "printing_tcp = NULL".
(trace): Likewise.
(trace): Fix checks for incomplete line - it was working wrongly if last syscall was exit.
(printleader): Set printing_tcp.
(printtrailer): Remove this function.
* syscall.c: Remove tcp_last variable.
(trace_syscall_entering): Don't set printing_tcp, printleader call now does it.
(trace_syscall_exiting): Convert printtrailer() call to "printing_tcp = NULL".
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
text data bss dec hex filename
238454 664 28772 267890 41672 strace.before
238106 664 28676 267446 414b6 strace
* defs.h: Add TIMESPEC_TEXT_BUFSIZE and TIMEVAL_TEXT_BUFSIZE defines.
Add 'int special' parameter to sprinttv().
* time.c (sprinttv): Add 'int special' parameter, and use it
similarly to 'int special' parameter of printtv_bitness().
(printtv_bitness): Use sprinttv() instead of duplicating its code.
(print_timespec): Use sprint_timespec() instead of duplicating
its code.
* desc.c (decode_select): Use TIMEVAL_TEXT_BUFSIZE instead of 128
when checking remaining buffer size.
* net.c (sys_recvmsg): Use TIMESPEC_TEXT_BUFSIZE instead of 128
for static buffer size.
* stream.c (decode_poll): Use TIMESPEC_TEXT_BUFSIZE instead of 128
when checking remaining buffer size.
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
On attempts to block or set SIGTRAP handler,
for example, using sigaction syscall, we generate
an additional SIGSTOP.
This change gets rid of this SIGSTOP sending/ignoring.
It appears to work just fine.
It also works if I force strace to not use PTRACE_O_TRACESYSGOOD,
which means strace stops will be marked with SIGTRAP,
not (SIGTRAP | 0x80) - I wondered maybe that's when
this hack is needed.
So, why we even have TCB_SIGTRAPPED? No one knows. It predates
version control: this code was present in the initial commit,
in 1999. No adequate comments, either.
Moreover, TCB_SIGTRAPPED is not set in sys_rt_sigaction
and sys_sigprocmask syscalls - the ones which are most usually
used to implement signal blocking, it is only set in obsolete
sys_signal, sys_sigaction, sys_sigsetmask, and in some dead
non-Linux code.
I think whatever bug it was fixing is gone long ago -
at least as long as sys_rt_sigaction is used by glibc.
Again, since glibc (and uclibc) uses sys_rt_sigaction
and sys_sigprocmask, modified code paths are not used
by most programs anyway.
* defs.h: Remove definition of TCB_SIGTRAPPED.
* signal.c (sys_sigvec): Don't set TCB_SIGTRAPPED and don't send SIGSTOP.
(sys_sigsetmask): Likewise.
(sys_sigaction): Likewise.
(sys_signal): Likewise.
* strace.c (trace): Remove code which executes if TCB_SIGTRAPPED is set.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
sys_sigreturn() performs ugly manipulations in order to show
signal mask which is restored by this syscall: on syscall entry,
fetches it from the stack, saves it in tcp->u_arg[]
(where it used to overflow this array - fixed sometime ago),
then retrieves the mask and displays it on syscall exit.
Apparently, the motivation is to make it slightly more obvious
to user that signal mask is restored only when this syscall returns.
IMO, this hardly justifies the necessary hacks. It is much easier
to display the mask at the point when we fetch it - on syscall entry.
While at it, I made it so that we do display returned value/errno.
I see no point in hiding it and showing uninformative "= ?" instead.
Example of pause() being interrupted by ALRM which has installed handler
which re-arms ALRM:
Before the patch:
rt_sigsuspend([INT]) = ? ERESTARTNOHAND (To be restarted)
--- {si_signo=SIGALRM, si_code=SI_KERNEL} (Alarm clock) ---
alarm(1) = 0
sigreturn() = ? (mask now [INT])
After:
rt_sigsuspend([INT]) = ? ERESTARTNOHAND (To be restarted)
--- {si_signo=SIGALRM, si_code=SI_KERNEL} (Alarm clock) ---
alarm(1) = 0
sigreturn() (mask [INT]) = -1 EINTR (Interrupted system call)
* defs.h: Declare struct pt_regs i386_regs and struct pt_regs x86_64_regs.
* syscall.c: Remove "static" keywork from these structures' definitions.
* signal.c (sys_sigreturn): Display mask on enter, not on exit.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
On syscall entry, save current personality in the tcb structure
along with scno.
On syscall exit, restore current personality from the tcb structure.
* defs.h (struct tcb) [SUPPORTED_PERSONALITIES > 1]: Add currpers
field.
* strace.c (alloc_tcb) [SUPPORTED_PERSONALITIES > 1]: Initialize
tcp->currpers.
* syscall.c (update_personality) [SUPPORTED_PERSONALITIES > 1]: New
function.
(get_scno, trace_syscall_exiting): Use it.
Reported-by: Michael A Fetterman <mafetter@nvidia.com>
We set ptrace options when we see post-attach SIGSTOP.
This is wrong: it's better to set them right away on the very first
stop (whichever it will be). It also will make adding SEIZE support easier,
since SEIZE has no post-attach SIGSTOP.
We do it by adding a new bit, TCB_IGNORE_ONE_SIGSTOP, and treating
TCB_STARTUP and TCB_IGNORE_ONE_SIGSTOP as two slightly different things.
* defs.h: Add a new flag bit, TCB_IGNORE_ONE_SIGSTOP.
* process.c (internal_fork): Set TCB_IGNORE_ONE_SIGSTOP on a newly added child.
* strace.c (startup_attach): Set TCB_IGNORE_ONE_SIGSTOP after attach.
Fix a case when "strace -p PID" found PID dead but sone other of its threads
still alive.
(startup_child): Set TCB_IGNORE_ONE_SIGSTOP after attach, _if needed_.
This fixes a bogus case where we can ignore a _real_ SIGSTOP on NOMMU.
(detach): Perform anti-SIGSTOP dance only if TCB_IGNORE_ONE_SIGSTOP is set,
not if TCB_STARTUP is set.
(trace): Set TCB_IGNORE_ONE_SIGSTOP after attach.
Clear TCB_STARTUP and initialize tracee on the very first tracee stop.
Clear TCB_IGNORE_ONE_SIGSTOP when SIGSTOP is seen.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
After this change, we don't use strcat() anywhere.
* defs.h: Change sprinttv() return type to char *.
* time.c (sprinttv): Return pointer past last stored char.
* desc.c (decode_select): Change printing logic in order to eliminate
usage of strcat() - use stpcpy(), *outptr++ = ch, sprintf() instead.
Also reduce usage of strlen().
* stream.c (decode_poll): Likewise.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Before this change, registers were read with PTRACE_PEEKUSER
ptrace operation, one per register. This is slower than
fetching them all in one ptrace operation.
* defs.h: include asm/ptrace.h on X86_64 and I386.
* syscall.c: New static variables i386_regs and x86_64_regs.
Remove static eax/rax variables.
(get_scno): Fetch all registers with single PTRACE_GETREGS operation.
(get_syscall_result): Likewise.
(syscall_fixup_on_sysenter): Use PTRACE_GETREGS results in i386/x86_64_regs.
(syscall_enter): Set tcp->u_arg[i] from PTRACE_GETREGS results.
(get_error): Set tcp->u_rval, tcp->u_error from PTRACE_GETREGS results.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
tabto is used in many lines of strace output.
On glibc, tprintf("%*s", col - curcol, "") is noticeably slow
compared to tprintf(" "). Use the latter.
Observed ~15% reduction of time spent in userspace.
* defs.h: Drop extern declaration of acolumn. Make tabto()
take no parameters.
* process.c (sys_exit): Call tabto() with no parameters.
* syscall.c (trace_syscall_exiting): Call tabto() with no parameters.
* strace.c: Make acolumn static, add static char *acolumn_spaces.
(main): Allocate acolumn_spaces as a string of spaces.
(printleader): Call tabto() with no parameters.
(tabto): Use simpler method to print lots of spaces.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
gcc can't figure out on its own that this check can be done with
single compare, and does two compares. We can help it by casting
scno to unsigned long: ((unsigned long)(scno) < nsyscalls)
* defs.h: New macro SCNO_IN_RANGE(long_var).
* count.c (count_syscall): Use SCNO_IN_RANGE() instead of open-coded check.
* syscall.c (getrval2): Use SCNO_IN_RANGE() instead of open-coded check.
This fixes a bug: missing check for scno < 0 and scno > nsyscalls
instead of scno >= nsyscalls.
(get_scno): Use SCNO_IN_RANGE() instead of open-coded check.
This fixes a bug: scno > nsyscalls instead of scno >= nsyscalls.
(known_scno): Use SCNO_IN_RANGE() instead of open-coded check.
(internal_syscall): Likewise.
(syscall_enter): Likewise.
(trace_syscall_entering): Likewise.
(get_error): Likewise.
(trace_syscall_exiting): Likewise.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Currently, get_scno does *much* more than "get syscall no".
It checks for post-execve SIGTRAP. It checks for changes
in personality. It retrieves params on entry and registers on exit.
Worse still, it is different in different architectures: for example,
for AVR32 regs are fetched in get_scno(), while for e.g. I386
it is done in syscall_enter().
Another problem is that get_scno() is called on both syscall entry and
syscall exit, which is stupid: we don't need to know scno on syscall
exit, it is already known from last syscall entry and stored in
tcp->scno! In essence, get_scno() does two completely different things
on syscall entry and on exit, they are just mixed into one bottle, like
shampoo and conditioner.
The following patches will try to improve this situation.
This change duplicates get_scno into identical get_scno_on_sysenter,
get_scno_on_sysexit functions. Call them in syscall enter and syscall
exit, correspondingly.
* defs.h: Rename get_scno to get_scno_on_sysenter; declare it only
if USE_PROCFS.
* strace.c (proc_open): Call get_scno_on_sysenter instead of get_scno.
* syscall.c (get_scno): Split into two (so far identical) functions
get_scno_on_sysenter and get_scno_on_sysexit.
(trace_syscall_entering): Call get_scno_on_sysenter instead of get_scno.
(trace_syscall_exiting): Call get_scno_on_sysexit instead of get_scno.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
* defs.h: Define MAX_ARGS to 6 for all Linux arches.
* linux/ia64/syscallent.h: Change all 8-argument printargs
to MA (MAX_ARGS).
linux/mips/syscallent.h: Change all two 7-argument printargs
to MA (MAX_ARGS).
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Usage -1 as argument count in syscallent tables
necessitates the check for it, a-la:
if (sysent[tcp->scno].nargs != -1)
tcp->u_nargs = sysent[tcp->scno].nargs;
else
tcp->u_nargs = MAX_ARGS;
which is stupid: we waste cycles checking something which
is constant and known at compile time.
* defs.h: Make struct sysent::nargs unsigned.
* freebsd/i386/syscallent.h: Replace nargs of -1 with MA.
* linux/s390/syscallent.h: Likewise.
* linux/s390x/syscallent.h: Likewise.
* svr4/syscallent.h: Likewise.
* freebsd/syscalls.pl: Likewise in generator script.
* syscallent.sh: Likewise in generator script.
* syscall.c: Add define MA MAX_ARGS / undef MA around includes
of syscallent[N].h.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
* defs.h: Explain TCB_INSYSCALL and TCB_WAITEXECVE bits in detail.
* strace.c (choose_pfd): Use entering/exiting macros instead of direct check
for TCB_INSYSCALL.
* syscall.c (get_scno): Use entering/exiting macros instead of direct check
for TCB_INSYSCALL. Fix comments about post-execve SIGTRAP.
(syscall_fixup): Use entering/exiting instead of direct check
for TCB_INSYSCALL. Add a comment what "not a syscall entry" message
usually means. Change wrong "stray syscall exit" messages into
"not a syscall entry" ones.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
* defs.h (count_syscall): Change return type from int to void.
* count.c (count_syscall): Change return type from int to void.
* syscall.c (trace_syscall_exiting): Change code around call
to count_syscall accordingly.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
* defs.h: Make struct tcb::pfd fields conditional on USE_PROCFS.
* strace.c (alloc_tcb): Use tcp->pfd only if USE_PROCFS.
(droptcb): Likewise.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Trivial shuffling of data tables puts them all in one file,
allowing gcc to see their sizes and eliminate variables
which store these sizes.
Surprisingly, in C mode gcc does not optimize out static const int
variables. Help it by using enums instead.
* defs.h: Stop exporting ioctlent{0,1,2}, nioctlents{0,1,2},
signalent{0,1,2}, nsignals{0,1,2}.
* ioctl.c: Remove definitions of ioctlent{,0,1,2} and nioctlents{,0,1,2}.
* signal.c: Remove definitions of signalent{,0,1,2} and nsignals{,0,1,2}.
* syscall.c: Move above definitions to this file. Make them static const
or enums if suitable.
* defs.h (set_personality): Change return type to void.
* syscall.c (set_personality): Change return type to void.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
* defs: Change struct tcb::flags type from short to int.
This results in smaller code at least on x86.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
* defs.h (addflags): Change return type from int to void.
* util.c (addflags): Change return type from int to void.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
I noticed that tcp->u_args[MAX_ARGS] array is way larger than
I'd expect: for all arches except HPPA it has 32 (!) elements.
I looked at the code and so far I spotted only one abuser of
this fact: sys_sigreturn. On several arches, it saves sigset_t
into tcp->u_args[1...N] on entry and prints it on exit, a-la
memcpy(&tcp->u_arg[1], &sc.oldmask[0], sizeof(sigset_t))
The problem here is that in glibc sigset_t is insanely large:
128 bytes, and using sizeof(sigset_t) in memcpy will overrun
&tcp->u_args[1] even with MAX_ARGS == 32:
On 32 bits, sizeof(tcp->u_args) == 32*4 == 128 bytes!
We may already have a bug there!
This commit changes the code to save NSIG / 8 bytes only.
NSIG can't ever be > 256, and in practice is <= 129,
thus NSIG / 8 is <= 16 bytes == 4 32-bit words,
and even MAX_ARGS == 5 should be enough for saving signal masks.
* defs.h: Reduce MAX_ARGS for X86_64 and I386 from 32 to 8
for FreeBSD and to 6 for everyone else. Add comment about current
state of needed MAX_ARGS.
* signal.c: Add comment about size of sigset_t.
(sprintsigmask): Reduce static string buffer from 8k to 2k.
(sys_sigreturn): Fix sigset saving to save only NSIG / 8 bytes,
not sizeof(sigset_t) bytes.
* linux/mips/syscallent.h: Reduce nargs of printargs-type syscall to 7.
* linux/arm/syscallent.h: Reduce nargs of printargs-type syscall to 6.
* linux/i386/syscallent.h: Likewise.
* linux/m68k/syscallent.h: Likewise.
* linux/powerpc/syscallent.h: Likewise.
* linux/s390/syscallent.h: Likewise.
* linux/s390x/syscallent.h: Likewise.
* linux/sh/syscallent.h: Likewise.
* linux/sh64/syscallent.h: Likewise.
* linux/sparc/syscallent.h: Likewise.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
* defs.h: Add/reformat comments.
* signal.c: Remove wrong comment. Add warning directive
when we detect that NSIG is undefined. Add comment about
NSIG on ARM. Fix typo in comment.
(signame): Reformat code a bit without changes to logic.
Shorten static buffer.
(sys_rt_sigprocmask): Remove stray empty line.
* syscall.c: Add warning directive when we detect that
NSIG is undefined. Add comment about NSIG on ARM.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
tcp->parent is used for only two things:
(1) to send signal on detach via tgkill (need to know tgid).
Solution: use tkill, it needs only tid.
(2) to optimize out ptrace options setting for new tracees.
Not a big deal if we drop this optimization: "set options" op is fast,
doing it just one extra time once per each tracee is hardly measurable.
TCB_CLONE_THREAD is a misnomer. It used only to flag sibling we attached to
in startup_attach. This is used to prevent infinite recursive rescanning
of /proc/PID/task.
Despite the name, there is no guarantee it is set only on non-leader:
if one would run "strace -f -p THREAD_ID" and THREAD_ID is *not*
a thread leader, strace will happily attach to it and all siblings
and will think that THREAD_ID is the leader! Which is a bug, but
since we no longer detach when we think tracee is going to die,
this bug no longer matters, because we do not use the knowledge
about thread group leaders for anything. (We used it to delay
leader's exit).
IOW: after this patch strace has no need to know about threads, parents
and children, and so on. Therefore it does not track that information.
It treats all tracees as independent entities. Overall,
this simplifies code a lot.
* defs.h: Add TCB_ATTACH_DONE flag, remove TCB_CLONE_THREAD flag
and struct tcb::parent field.
* process.c (internal_fork): Don't set tcpchild->parent.
* strace.c (startup_attach): Use TCB_ATTACH_DONE flag instead of
TCB_CLONE_THREAD to avoid attach attempts on already-attached threads.
Unlike TCB_CLONE_THREAD, TCB_ATTACH_DONE bit is used only temporarily,
and only in this function. We clear it on every tcb before we return.
(detach): Use tkill instead of tgkill.
(trace): Set ptrace options on new tracees unconditionally,
not only when tcp->parent == NULL.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Since we no longer suspend waitpid'ing tracees, we have only one case when
we suspend tracee: when we pick up a new tracee created by clone/fork/vfork.
Background: on some other OSes, attach to child is done this way:
get fork's result (pid), loop ptrace(PTRACE_ATTACH) until you hook up
new process/thread. This is ugly and not safe, but what matters for us
is that it doesn't require suspending. Suspending is required
on Linux only, because on Linux attach to child is done differently.
On Linux, we use two methods of catching new tracee:
adding CLONE_THREAD bit to syscall (if needed, we change
[v]fork into clone before that), or using ptrace options.
In both cases, it may be so that new tracee appears before one which
created it returns from syscall. In this case, current code
suspends new tracee until its creator returns. Only then
strace can determine who is its parent (it needs child's pid for this,
which is visible in parent's [v]fork/clone result).
This is inherently racy. For example, what if SIGKILL kills
creator after it succeeded creating child, but before it returns?
Looks like we will have child suspended forever.
But after previous commit, we DO NOT NEED parent<->child link for anything.
Therefore we do not need suspending too. Bingo!
This patch removes suspending code. Now new tracees will be continued
right away. Next patch will remove tcp->parent member.
* defs.h: Remove TCB_SUSPENDED constant
* process.c (handle_new_child): Delete this function.
(internal_fork): Do not call handle_new_child on syscall exit.
* strace.c (handle_ptrace_event): Delete this function.
(trace): Do not suspend new child; remove all handling
of now impossible TCB_SUSPENDED condition.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
