[PATCH] S390: Fix struct sigaction for 31bit in kernel_sigaction.h.

[Stefan Liebler <stli at linux dot vnet dot ibm dot com>]

Hi,

the recent commit b4a5d26d8835d972995f0a0a2f805a8845bafa0b
"linux: Consolidate sigaction implementation" changed the definition
of struct sigaction for s390 (31bit). Unfortunately the order of the
fields were wrong.

This leads to blocking testcases e.g. nptl/tst-sem11. A thread which 
blocks due to sem_wait() is cancelled via pthread_cancel() and the 
signal-handler sigcancel_handler (see <glibc-src>/nptl/nptl-init.c is 
called. But it just returns as the siginfo_t argument is not setup by 
the kernel. Then the main-thread is blocking due to pthread_join().

The flag SA_SIGINFO is set in sa_flags in struct sigaction and is copied 
to the "kernel_sigaction.h" struct by the sigaction() call, but due to 
the wrong ordering of the struct fields, the kernel does not recognize it.

This patch is fixing the definition of s390-kernel_sigaction.h struct 
for 31bit.

Okay to commit?

Bye
Stefan

ChangeLog:

	* sysdeps/unix/sysv/linux/s390/kernel_sigaction.h
	(struct kernel_sigaction): Use the same definition
	on 31bit as is used on 64bit.

commit 404f5a0eac37d4c85e027c7b7fc64cb3ecbfc894
Author: Stefan Liebler <stli@linux.vnet.ibm.com>
Date:   Wed Apr 11 16:57:48 2018 +0200

    S390: Fix struct sigaction for 31bit in kernel_sigaction.h.
    
    The recent commit b4a5d26d8835d972995f0a0a2f805a8845bafa0b
    "linux: Consolidate sigaction implementation" changed the definition
    of struct sigaction for s390 (31bit). Unfortunately the order of the
    fields were wrong.
    
    This leads to blocking testcases e.g. nptl/tst-sem11.
    A thread which blocks due to sem_wait() is cancelled via pthread_cancel()
    and the signal-handler sigcancel_handler (see <glibc-src>/nptl/nptl-init.c
    is called.
    But it just returns as the siginfo_t argument is not setup by the kernel.
    Then the main-thread is blocking due to pthread_join().
    
    The flag SA_SIGINFO is set in sa_flags in struct sigaction and
    is copied to the "kernel_sigaction.h" struct by the sigaction() call,
    but due to the wrong ordering of the struct fields,
    the kernel does not recognize it.

diff --git a/sysdeps/unix/sysv/linux/s390/kernel_sigaction.h b/sysdeps/unix/sysv/linux/s390/kernel_sigaction.h
index a8beaf7347..28a1aa0f37 100644
--- a/sysdeps/unix/sysv/linux/s390/kernel_sigaction.h
+++ b/sysdeps/unix/sysv/linux/s390/kernel_sigaction.h
@@ -11,15 +11,30 @@ struct kernel_sigaction
     void (*_sa_sigaction)(int, siginfo_t *, void *);
   } _u;
 #define k_sa_handler _u._sa_handler
-#ifndef __s390x__
-  sigset_t sa_mask;
-  unsigned long sa_flags;
-  void (*sa_restorer)(void);
-#else
+  /* The rt_sigaction-syscall (which is currently used in glibc)
+     expects this struct on 31bit (real 31bit-kernel or compat-mode) and 64bit!
+     See <kernel-src>/include/linux/signal_types.h: struct sigaction
+     or <kernel-src>/include/linux/compat.h: struct compat_sigaction.
+
+     The sigaction-syscall (which is currently not used in glibc and was never
+     used on s390x 64bit) expects the kernel struct old_sigaction
+     and struct compat_old_sigaction. There the order of the fields is:
+     -_sa_handler / _sa_sigaction
+     -sa_mask
+     -sa_flags
+     -sa_restorer
+     See the same kernel-headers as mentioned above.
+
+     The definition of struct sigaction in
+     <kernel-src>/arch/s390/include/uapi/asm/signal.h
+     (only used for kernel-uapi)
+     is currently using the struct-definition for rt_sigaction-syscall on 64bit
+     and the struct-definition for sigaction-syscall on 31bit.
+     Thus we can't simply copy this definition here.
+     Note: This kernel-uapi-defintion will also be fixed!  */
   unsigned long sa_flags;
   void (*sa_restorer)(void);
   sigset_t sa_mask;
-#endif
 };
 
 #define SET_SA_RESTORER(kact, act)             \