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| author | Michael Kerrisk <mtk.manpages@gmail.com> | 2017-05-22 22:29:00 +0200 |
|---|---|---|
| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2017-11-08 08:36:50 +0100 |
| commit | cfdc176b445ceba00c920bc0cd311a6c7d91a8de (patch) | |
| tree | 2feabb8abcafbf8880beca6c3ed3749022a06b69 | |
| parent | e4631a3524995913b2820404100e22f549450f74 (diff) | |
| download | man-pages-cfdc176b445ceba00c920bc0cd311a6c7d91a8de.tar.gz | |
sigaltstack.2: Document SS_AUTODISARM flag added in Linux 4.7
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
| -rw-r--r-- | man2/sigaltstack.2 | 53 |
1 files changed, 49 insertions, 4 deletions
diff --git a/man2/sigaltstack.2 b/man2/sigaltstack.2 index 0a21eb7b4d..0c4fd035f5 100644 --- a/man2/sigaltstack.2 +++ b/man2/sigaltstack.2 @@ -1,5 +1,5 @@ '\" t -.\" Copyright (c) 2001, Michael Kerrisk <mtk.manpages@gmail.com> +.\" Copyright (c) 2001, 2017 Michael Kerrisk <mtk.manpages@gmail.com> .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this @@ -103,7 +103,27 @@ To establish a new alternate signal stack, the fields of this structure are set as follows: .TP .I ss.ss_flags -This field is set to zero. +This field contains either 0, or the following flag: +.RS +.TP +.BR SS_AUTODISARM " (since Linux 4.7)" +.\" commit 2a74213838104a41588d86fd5e8d344972891ace +.\" See tools/testing/selftests/sigaltstack/sas.c in kernel sources +Clear the alternate signal stack settings on entry to the signal handler. +When the signal handler returns, +the previous alternate signal stack settings are restored. +.IP +This flag was added in order make it safe +to switch away from the signal handler with +.BR swapcontext (3). +Without this flag, a subsequently handled signal will corrupt +the state of the switched-away signal handler. +On kernels where this flag is not supported, +.BR sigaltstack () +fails with the error +.BR EINVAL +when this flag is supplied. +.RE .TP .I ss.ss_sp This field specifies the starting address of the stack. @@ -120,8 +140,10 @@ size required to execute a signal handler. .PP To disable an existing stack, specify \fIss.ss_flags\fP as \fBSS_DISABLE\fP. -In this case, the remaining fields -in \fIss\fP are ignored. +In this case, the kernel ignores any other flags in +.IR ss.ss_flags +and the remaining fields +in \fIss\fP. .PP If \fIold_ss\fP is not NULL, then it is used to return information about the alternate signal stack which was in effect prior to the @@ -139,6 +161,25 @@ currently executing on it.) .TP .B SS_DISABLE The alternate signal stack is currently disabled. +.IP +Alternatively, this value is returned if the process is currently +executing on an alternate signal stack that was established using the +.B SS_AUTODISARM +flag. +In this case, it is safe to switch away from the signal handler with +.BR swapcontext (3). +It is also possible to set up a different alternative signal stack +using a further call to +.BR sigaltstack (). +.\" FIXME Was it intended that one can set up a different alternative +.\" signal stack in this scenario? (In passing, if one does this, the +.\" sigaltstack(NULL, &old_ss) now returns old_ss.ss_flags==SS_AUTODISARM +.\" rather than old_ss.ss_flags==SS_DISABLE. The API design here seems +.\" confusing... +.TP +.B SS_AUTODISARM +The alternate signal stack has been marked to be autodisarmed +as described above. .PP By specifying .I ss @@ -184,6 +225,10 @@ T} Thread safety MT-Safe .TE .SH CONFORMING TO POSIX.1-2001, POSIX.1-2009, SUSv2, SVr4. + +The +.B SS_AUTODISARM +flag is a Linux extension. .SH NOTES The most common usage of an alternate signal stack is to handle the .B SIGSEGV |