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README-linux-ptrace: correct the description of suppressed signals

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Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
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Denys Vlasenko 2012-02-09 19:57:52 +01:00
parent bdec9cbceb
commit 0ed9947c14
1 changed files with 8 additions and 12 deletions
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README-linux-ptrace
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@ -53,7 +53,7 @@ process (all its threads), even if some threads of the process are
ptraced.
Tracer can kill a tracee with ptrace(PTRACE_KILL, pid, 0, 0). This
opeartion is deprecated, use kill/tgkill(SIGKILL) instead.
operation is deprecated, use kill/tgkill(SIGKILL) instead.
^^^ Oleg prefers to deprecate it instead of describing (and needing to
support) PTRACE_KILL's quirks.
@ -165,17 +165,13 @@ Note that sig value may be different from WSTOPSIG(status) value -
tracer can cause a different signal to be injected.
Note that suppressed signal still causes syscalls to return
prematurely. Restartable syscalls will be restarted (tracer will
observe tracee to execute restart_syscall(2) syscall if tracer uses
PTRACE_SYSCALL), non-restartable syscalls (for example, nanosleep) may
return with -EINTR even though no observable signal is injected to the
tracee.
Note that restarting ptrace commands issued in ptrace-stops other than
signal-delivery-stop are not guaranteed to inject a signal, even if sig
is nonzero. No error is reported, nonzero sig may simply be ignored.
Ptrace users should not try to "create new signal" this way: use
tgkill(2) instead.
prematurely. Kernel should always restart the syscall in this case:
tracer would observe a new syscall-enter-stop for the same syscall,
or, in case of syscalls returning ERESTART_RESTARTBLOCK,
tracer would observe a syscall-enter-stop for restart_syscall(2)
syscall. There may still be bugs in this area which cause some syscalls
to instead return with -EINTR even though no observable signal
was injected to the tracee.
This is a cause of confusion among ptrace users. One typical scenario
is that tracer observes group-stop, mistakes it for