RE: [PATCH 1/3] [POC] test implementaion of rt-signals

[Johannes Kirchmair <johannes.kirchmair@sigmatek.at>]

> -----Original Message-----
> From: Jan Kiszka <jan.kiszka@siemens.com>
> Sent: Freitag, 12. Mai 2023 19:39
> To: Johannes Kirchmair <johannes.kirchmair@sigmatek.at>;
> xenomai@lists.linux.dev; Schaffner, Tobias <tobias.schaffner@siemens.com>
> Subject: Re: [PATCH 1/3] [POC] test implementaion of rt-signals
> 
> CAUTION: External E-Mail !
> 
> On 09.05.23 15:17, Johannes Kirchmair wrote:
> > Hello Jan and Tobias,
> >
> > I just dropped the patches on the mailing list.
> > For the dovetail functions I took a rather naive approach, using most of the
> frame setup code provided by Linux.
> > I just tested it for 32bit and 64bit x86 Applications and it seems to work.
> >
> > I also added a tool rt_signal_hist that runs in a cycle and measures the time an
> exception handling takes.
> > It is afterwards put into an txt file that reassembles an histogram of the timings.
> >
> > Unfortunately as a 32bit application the rt_signal_hist tool does not run to
> completion, printing the following:
> > " Xenomai/cobalt: sleeping while holding mutex
> > CPU time limit exceeded"
> >
> > Maybe the naive approach is not so reliable ;-/
> > Hope I find the time the look into it.
> >
> 
> I looked into the x86 signalframe helpers before and found some traces
> of locking that make them incompatible - if I rember correctly. After
> that, I dropped the idea of just removing the "static".
Do you remember where you saw the locking in the code, was it rather obvious or hidden?
When I had a look I did not see locking in the functions I used, so I thought dropping the "static" would be fine.

Would you still try to use some of the functions Linux provides?

> 
> > Sorry for not putting more effort into this so fare.
> >
> > The next most important step in my opinion would be to define a clean interface
> into dovetail for the signal frame setup and restoring.
> > Actually that's the task I consider one of the harder and I am not so sure how to
> approach this.
> >
> 
> Exactly, and we need to involve Philippe now soon. Let me medidate over
> some interface options as well. Will pick up if you don't find the time
> soon.
At the moment, I am not event sure, what the next task would be to continue with this feature.
As I am not sure how to define the interface for dovetail, I hesitate a little bit to change the code as it is right now.

What I could do is have a look why my hist-tool breaks in the 32bit user space case.

I also could try to provide an idea for the interface, but I am not so sure if it is of good use, as my knowledge of the Kernels internal workings is still rather limited.

Best regards Johannes

> 
> Jan
> 
> > Best regards
> > Johannes
> >
> >> -----Original Message-----
> >> From: Johannes Kirchmair <johannes.kirchmair@sigmatek.at>
> >> Sent: Dienstag, 9. Mai 2023 15:14
> >> To: xenomai@lists.linux.dev
> >> Cc: Johannes Kirchmair <johannes.kirchmair@sigmatek.at>
> >> Subject: [PATCH 1/3] [POC] test implementaion of rt-signals
> >>
> >> We implement rt signals to handle exceptions in rt stage.
> >>
> >> This is done using dovetail specific functions for setting up the signal
> >> frame.
> >>
> >> This can be used to handle fpe exceptions on the fly, like fixing
> >> division by zero. An other use case are breakpoints, implemented using the
> >> illegal opcode exception. The real time handling of the breakpoints would
> >> be handy for conditional breakpoints or also for stopping watchdogs and
> >> other tasks in time.
> >>
> >> Signed-off-by: Johannes Kirchmair <johannes.kirchmair@sigmatek.at>
> >> ---
> >>  include/cobalt/kernel/ppd.h                   |  3 +
> >>  include/cobalt/kernel/thread.h                |  2 +
> >>  include/cobalt/signal.h                       |  2 +
> >>  include/cobalt/uapi/syscall.h                 |  6 ++
> >>  kernel/cobalt/arch/x86/Makefile               |  2 +-
> >>  .../arch/x86/include/asm/xenomai/thread.h     | 13 ++++
> >>  kernel/cobalt/arch/x86/signal_ia32.c          | 75 +++++++++++++++++++
> >>  kernel/cobalt/arch/x86/signal_ia64.c          | 26 +++++++
> >>  kernel/cobalt/dovetail/kevents.c              |  5 ++
> >>  kernel/cobalt/posix/process.c                 |  3 +-
> >>  kernel/cobalt/posix/syscall.c                 | 28 +++++++
> >>  kernel/cobalt/posix/syscall32.c               | 16 ++++
> >>  kernel/cobalt/thread.c                        | 39 ++++++++++
> >>  lib/cobalt/arch/x86/Makefile.am               |  2 +-
> >>  lib/cobalt/arch/x86/sigreturn.c               | 32 ++++++++
> >>  lib/cobalt/internal.h                         |  2 +
> >>  lib/cobalt/signal.c                           | 13 ++++
> >>  17 files changed, 266 insertions(+), 3 deletions(-)
> >>  create mode 100644 kernel/cobalt/arch/x86/signal_ia32.c
> >>  create mode 100644 kernel/cobalt/arch/x86/signal_ia64.c
> >>  create mode 100644 lib/cobalt/arch/x86/sigreturn.c
> >>
> >> diff --git a/include/cobalt/kernel/ppd.h b/include/cobalt/kernel/ppd.h
> >> index f0079fe6e..fb2f682da 100644
> >> --- a/include/cobalt/kernel/ppd.h
> >> +++ b/include/cobalt/kernel/ppd.h
> >> @@ -22,6 +22,7 @@
> >>  #include <linux/types.h>
> >>  #include <linux/atomic.h>
> >>  #include <linux/rbtree.h>
> >> +#include <linux/signal.h>
> >>  #include <cobalt/kernel/heap.h>
> >>
> >>  struct cobalt_umm {
> >> @@ -32,6 +33,8 @@ struct cobalt_umm {
> >>
> >>  struct cobalt_ppd {
> >>      struct cobalt_umm umm;
> >> +    void __user *sighand[_NSIG];
> >> +    void __user *sigrestorer;
> >>      atomic_t refcnt;
> >>      char *exe_path;
> >>      struct rb_root fds;
> >> diff --git a/include/cobalt/kernel/thread.h b/include/cobalt/kernel/thread.h
> >> index b79cb8429..33d468419 100644
> >> --- a/include/cobalt/kernel/thread.h
> >> +++ b/include/cobalt/kernel/thread.h
> >> @@ -574,6 +574,8 @@ static inline void
> xnthread_propagate_schedparam(struct
> >> xnthread *curr)
> >>              __xnthread_propagate_schedparam(curr);
> >>  }
> >>
> >> +int xnthread_handle_rt_signals(unsigned int trapnr, struct pt_regs *regs);
> >> +
> >>  extern struct xnthread_personality xenomai_personality;
> >>
> >>  /** @} */
> >> diff --git a/include/cobalt/signal.h b/include/cobalt/signal.h
> >> index 62694f93a..3d6540aff 100644
> >> --- a/include/cobalt/signal.h
> >> +++ b/include/cobalt/signal.h
> >> @@ -54,6 +54,8 @@ COBALT_DECL(int, kill(pid_t pid, int sig));
> >>  COBALT_DECL(int, sigqueue(pid_t pid, int sig,
> >>                        const union sigval value));
> >>
> >> +int cobalt_rt_signal(int sig, void (*handler)(int, siginfo_t *, void *));
> >> +
> >>  #ifdef __cplusplus
> >>  }
> >>  #endif
> >> diff --git a/include/cobalt/uapi/syscall.h b/include/cobalt/uapi/syscall.h
> >> index 9646a0d97..6307fae7f 100644
> >> --- a/include/cobalt/uapi/syscall.h
> >> +++ b/include/cobalt/uapi/syscall.h
> >> @@ -137,6 +137,12 @@
> >>  #define sc_cobalt_recvmmsg64                        114
> >>  #define sc_cobalt_cond_wait_prologue64              115
> >>
> >> +/*
> >> + * Sigmatek specific syscalls
> >> + */
> >> +#define sc_cobalt_sigreturn                 120
> >> +#define sc_cobalt_sigaction                 121
> >> +
> >>  #define __NR_COBALT_SYSCALLS                        128 /* Power of 2 */
> >>
> >>  #endif /* !_COBALT_UAPI_SYSCALL_H */
> >> diff --git a/kernel/cobalt/arch/x86/Makefile
> b/kernel/cobalt/arch/x86/Makefile
> >> index 93929b645..e725afbff 100644
> >> --- a/kernel/cobalt/arch/x86/Makefile
> >> +++ b/kernel/cobalt/arch/x86/Makefile
> >> @@ -1,5 +1,5 @@
> >>
> >>  obj-$(CONFIG_XENOMAI) += xenomai.o
> >> -xenomai-y := machine.o smi.o c1e.o
> >> +xenomai-y := machine.o smi.o c1e.o signal_ia32.o signal_ia64.o
> >>
> >>  ccflags-y := -I$(srctree)/arch/x86/xenomai/include -
> I$(srctree)/include/xenomai
> >> diff --git a/kernel/cobalt/arch/x86/include/asm/xenomai/thread.h
> >> b/kernel/cobalt/arch/x86/include/asm/xenomai/thread.h
> >> index 745c32467..4d004680b 100644
> >> --- a/kernel/cobalt/arch/x86/include/asm/xenomai/thread.h
> >> +++ b/kernel/cobalt/arch/x86/include/asm/xenomai/thread.h
> >> @@ -28,5 +28,18 @@
> >>  #define xnarch_fault_bp_p(__nr)             ((current->ptrace & PT_PTRACED)
> >> &&   \
> >>                                       ((__nr) == X86_TRAP_DB || (__nr) ==
> >> X86_TRAP_BP))
> >>  #define xnarch_fault_notify(__nr)   (!xnarch_fault_bp_p(__nr))
> >> +#define xnarch_fault_code(__regs)           ((__regs)->orig_ax)
> >> +int xnarch_setup_trap_info(unsigned int vector, struct pt_regs *regs,
> >> +                       long errcode, int *sig, struct kernel_siginfo *info);
> >> +
> >> +int xnarch_setup_rt_frame_ia32(int sig, void *handler, struct kernel_siginfo
> *si,
> >> +                      struct pt_regs *regs, void __user *restorer);
> >> +
> >> +int xnarch_rt_sigreturn_ia32(struct pt_regs *regs);
> >> +
> >> +int xnarch_setup_rt_frame_ia64(int sig, void *handler, struct kernel_siginfo
> *si,
> >> +                      struct pt_regs *regs, void __user *restorer);
> >> +
> >> +int xnarch_rt_sigreturn_ia64(struct pt_regs *regs);
> >>
> >>  #endif /* !_COBALT_X86_ASM_THREAD_H */
> >> diff --git a/kernel/cobalt/arch/x86/signal_ia32.c
> >> b/kernel/cobalt/arch/x86/signal_ia32.c
> >> new file mode 100644
> >> index 000000000..e78c8c4d4
> >> --- /dev/null
> >> +++ b/kernel/cobalt/arch/x86/signal_ia32.c
> >> @@ -0,0 +1,75 @@
> >> +#include <linux/signal.h>
> >> +#include <linux/uaccess.h>
> >> +#include <cobalt/kernel/thread.h>
> >> +
> >> +#include <asm/sigframe.h>
> >> +#include <asm/sighandling.h>
> >> +#include <asm/fpu/signal.h>
> >> +
> >> +int xnarch_setup_trap_info(unsigned int vector, struct pt_regs *regs,
> >> +                       long errcode, int *sig, struct kernel_siginfo *info)
> >> +{
> >> +    switch (vector) {
> >> +    case 0: /* divide_error */
> >> +            *sig = SIGFPE;
> >> +            info->si_signo = *sig;
> >> +            info->si_errno = 0;
> >> +            info->si_code = FPE_INTDIV;
> >> +            info->si_addr = (void __user *)regs->ip;
> >> +            return 0;
> >> +    case 1: /* trap_error */ {
> >> +            unsigned long condition;
> >> +            get_debugreg(condition, 6);
> >> +            set_debugreg(0, 7);
> >> +            *sig = SIGTRAP;
> >> +            info->si_signo = *sig;
> >> +            info->si_errno = errcode;
> >> +            info->si_code = get_si_code(condition);
> >> +            info->si_addr = (void __user *)regs->ip;
> >> +            return 0;
> >> +    }
> >> +    case 3: /* trap_error */
> >> +            *sig = SIGTRAP;
> >> +            info->si_signo = *sig;
> >> +            info->si_errno = errcode;
> >> +            info->si_code = SI_KERNEL;
> >> +            info->si_addr = (void __user *)regs->ip;
> >> +            return 0;
> >> +    case 6: /* invalid_op */
> >> +            *sig = SIGILL;
> >> +            info->si_signo = *sig;
> >> +            info->si_errno = 0;
> >> +            info->si_code = ILL_ILLOPN;
> >> +            info->si_addr = (void __user *)regs->ip;
> >> +            return 0;
> >> +    case 16: { /* coprocessor_error */
> >> +            *sig = SIGFPE;
> >> +
> >> +            info->si_signo = *sig;
> >> +            info->si_errno = 0;
> >> +            info->si_code = 0;
> >> +            info->si_addr = (void __user *)regs->ip;
> >> +            return 0;
> >> +    }
> >> +    default:
> >> +            break;
> >> +    }
> >> +
> >> +    return -ENOSYS;
> >> +}
> >> +
> >> +int xnarch_rt_sigreturn_ia32(struct pt_regs *regs)
> >> +{
> >> +    int ret;
> >> +
> >> +    ret = dovetail_restore_rt_signal_frame(regs);
> >> +    if (ret < 0)
> >> +            goto badframe;
> >> +
> >> +    return regs->ax;
> >> +
> >> +badframe:
> >> +    xnthread_call_mayday(xnthread_current(), SIGKILL);
> >> +    return -1;
> >> +}
> >> +
> >> diff --git a/kernel/cobalt/arch/x86/signal_ia64.c
> >> b/kernel/cobalt/arch/x86/signal_ia64.c
> >> new file mode 100644
> >> index 000000000..a7044db40
> >> --- /dev/null
> >> +++ b/kernel/cobalt/arch/x86/signal_ia64.c
> >> @@ -0,0 +1,26 @@
> >> +// SPDX-License-Identifier: GPL-2.0
> >> +/*
> >> + *  Copyright (C) 1991, 1992  Linus Torvalds
> >> + *  Copyright (C) 2000, 2001, 2002 Andi Kleen SuSE Labs
> >> + *
> >> + *  1997-11-28  Modified for POSIX.1b signals by Richard Henderson
> >> + *  2000-06-20  Pentium III FXSR, SSE support by Gareth Hughes
> >> + *  2000-2002   x86-64 support by Andi Kleen
> >> + */
> >> +
> >> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> >> +
> >> +
> >> +#include <linux/signal.h>
> >> +#include <linux/uaccess.h>
> >> +#include <cobalt/kernel/thread.h>
> >> +
> >> +#include <asm/sigframe.h>
> >> +#include <asm/sighandling.h>
> >> +#include <asm/fpu/signal.h>
> >> +
> >> +int xnarch_rt_sigreturn_ia64(struct pt_regs *regs)
> >> +{
> >> +    return dovetail_restore_rt_signal_frame(regs);
> >> +}
> >> +
> >> diff --git a/kernel/cobalt/dovetail/kevents.c b/kernel/cobalt/dovetail/kevents.c
> >> index 4da4f51b7..61417717b 100644
> >> --- a/kernel/cobalt/dovetail/kevents.c
> >> +++ b/kernel/cobalt/dovetail/kevents.c
> >> @@ -57,6 +57,9 @@ void handle_oob_trap_entry(unsigned int trapnr, struct
> >> pt_regs *regs)
> >>              xnsched_run();
> >>      }
> >>
> >> +    if (xnthread_handle_rt_signals(trapnr, regs) == 0)
> >> +            return;
> >> +
> >>      /*
> >>       * If we experienced a trap on behalf of a shadow thread
> >>       * running in primary mode, move it to the Linux domain,
> >> @@ -88,6 +91,8 @@ void handle_oob_trap_entry(unsigned int trapnr, struct
> >> pt_regs *regs)
> >>              xnstat_counter_inc(&thread->stat.pf);
> >>
> >>      xnthread_relax(xnarch_fault_notify(trapnr), SIGDEBUG_MIGRATE_FAULT);
> >> +
> >> +    return;
> >>  }
> >>
> >>  static inline int handle_setaffinity_event(struct dovetail_migration_data *d)
> >> diff --git a/kernel/cobalt/posix/process.c b/kernel/cobalt/posix/process.c
> >> index 1abc86f37..2069129cb 100644
> >> --- a/kernel/cobalt/posix/process.c
> >> +++ b/kernel/cobalt/posix/process.c
> >> @@ -738,9 +738,10 @@ void cobalt_unregister_debugged_thread(struct
> >> xnthread *thread)
> >>              cobalt_resume_debugged_process(process);
> >>  }
> >>
> >> +#ifdef CONFIG_SMP
> >> +
> >>  int cobalt_handle_setaffinity_event(struct task_struct *task)
> >>  {
> >> -#ifdef CONFIG_SMP
> >>      struct xnthread *thread;
> >>      spl_t s;
> >>
> >> diff --git a/kernel/cobalt/posix/syscall.c b/kernel/cobalt/posix/syscall.c
> >> index 46c4998e4..b4bd4c587 100644
> >> --- a/kernel/cobalt/posix/syscall.c
> >> +++ b/kernel/cobalt/posix/syscall.c
> >> @@ -277,6 +277,34 @@ static COBALT_SYSCALL(serialdbg, current,
> >>      return 0;
> >>  }
> >>
> >> +static COBALT_SYSCALL(sigreturn, current, (void))
> >> +{
> >> +    struct pt_regs *regs = task_pt_regs(current);
> >> +
> >> +    if (regs->cs == __USER_CS)
> >> +            xnarch_rt_sigreturn_ia64(regs);
> >> +    if (regs->cs == __USER32_CS)
> >> +            xnarch_rt_sigreturn_ia32(regs);
> >> +
> >> +    return __xn_reg_rval(regs);
> >> +}
> >> +
> >> +static COBALT_SYSCALL(sigaction, current, (int sig, void __user *handler,
> >> +                  void __user *restorer))
> >> +{
> >> +    struct cobalt_ppd *sys_ppd = cobalt_ppd_get(0);
> >> +
> >> +    if (sig < 0 || sig >= _NSIG)
> >> +            return -EINVAL;
> >> +
> >> +    sys_ppd->sighand[sig] = handler;
> >> +
> >> +    if (!sys_ppd->sigrestorer)
> >> +            sys_ppd->sigrestorer = restorer;
> >> +
> >> +    return 0;
> >> +}
> >> +
> >>  static void stringify_feature_set(unsigned long fset, char *buf, int size)
> >>  {
> >>      unsigned long feature;
> >> diff --git a/kernel/cobalt/posix/syscall32.c b/kernel/cobalt/posix/syscall32.c
> >> index b65a0a760..f8b21bfb2 100644
> >> --- a/kernel/cobalt/posix/syscall32.c
> >> +++ b/kernel/cobalt/posix/syscall32.c
> >> @@ -774,6 +774,22 @@ COBALT_SYSCALL32emu(sigqueue, conforming,
> >>      return ret ?: __cobalt_sigqueue(pid, sig, &val);
> >>  }
> >>
> >> +COBALT_SYSCALL32emu(sigaction, current,
> >> +                (int sig, void __user *handler, void __user *restorer))
> >> +{
> >> +    struct cobalt_ppd *sys_ppd = cobalt_ppd_get(0);
> >> +
> >> +    if (sig < 0 || sig >= _NSIG)
> >> +            return -EINVAL;
> >> +
> >> +    sys_ppd->sighand[sig] = handler;
> >> +
> >> +    if (!sys_ppd->sigrestorer)
> >> +            sys_ppd->sigrestorer = restorer;
> >> +
> >> +    return 0;
> >> +}
> >> +
> >>  COBALT_SYSCALL32emu(monitor_wait, nonrestartable,
> >>                  (struct cobalt_monitor_shadow __user *u_mon,
> >>                   int event, const struct old_timespec32 __user *u_ts,
> >> diff --git a/kernel/cobalt/thread.c b/kernel/cobalt/thread.c
> >> index 41804b24f..71f97c481 100644
> >> --- a/kernel/cobalt/thread.c
> >> +++ b/kernel/cobalt/thread.c
> >> @@ -25,6 +25,7 @@
> >>  #include <linux/signal.h>
> >>  #include <linux/pid.h>
> >>  #include <linux/sched.h>
> >> +#include <asm/sighandling.h>
> >>  #include <uapi/linux/sched/types.h>
> >>  #include <cobalt/kernel/sched.h>
> >>  #include <cobalt/kernel/timer.h>
> >> @@ -43,6 +44,7 @@
> >>  #include <pipeline/inband_work.h>
> >>  #include <pipeline/sched.h>
> >>  #include <trace/events/cobalt-core.h>
> >> +#include "posix/process.h"
> >>  #include "debug.h"
> >>
> >>  static DECLARE_WAIT_QUEUE_HEAD(join_all);
> >> @@ -2520,6 +2522,43 @@ int xnthread_killall(int grace, int mask)
> >>  }
> >>  EXPORT_SYMBOL_GPL(xnthread_killall);
> >>
> >> +int xnthread_handle_rt_signals(unsigned int trapnr, struct pt_regs *regs)
> >> +{
> >> +    struct ksignal ksig;
> >> +
> >> +    unsigned int vector = trapnr;
> >> +    unsigned int code = xnarch_fault_code(regs);
> >> +    struct cobalt_ppd *sys_ppd;
> >> +    int sig, ret = 0;
> >> +    struct kernel_siginfo si;
> >> +
> >> +    code = xnarch_fault_code(regs);
> >> +    ret = xnarch_setup_trap_info(vector, regs, code, &sig, &si);
> >> +    if (ret || sig == 0)
> >> +            return 1;
> >> +
> >> +    sys_ppd = cobalt_ppd_get(0);
> >> +    if (sig >= _NSIG ||
> >> +        sys_ppd->sighand[sig] == NULL ||
> >> +        sys_ppd->sighand[sig] == SIG_DFL)
> >> +            return 1;
> >> +
> >> +    if (sys_ppd->sigrestorer == NULL)
> >> +            return 1;
> >> +
> >> +    ksig.sig = sig;
> >> +    memcpy(&ksig.info, &si, sizeof(si));
> >> +    ksig.ka.sa.sa_flags = SA_SIGINFO | SA_RESTORER;
> >> +    ksig.ka.sa.sa_restorer = sys_ppd->sigrestorer;
> >> +    ksig.ka.sa.sa_handler = sys_ppd->sighand[sig];
> >> +
> >> +    ret = dovetail_setup_rt_signal_frame(&ksig, regs);
> >> +    if (ret)
> >> +            return 1;
> >> +
> >> +    return 0;
> >> +}
> >> +
> >>  /* Xenomai's generic personality. */
> >>  struct xnthread_personality xenomai_personality = {
> >>      .name = "core",
> >> diff --git a/lib/cobalt/arch/x86/Makefile.am b/lib/cobalt/arch/x86/Makefile.am
> >> index a5095be3d..14f5eff97 100644
> >> --- a/lib/cobalt/arch/x86/Makefile.am
> >> +++ b/lib/cobalt/arch/x86/Makefile.am
> >> @@ -2,7 +2,7 @@ noinst_LTLIBRARIES = libarch.la
> >>
> >>  libarch_la_LDFLAGS = @XENO_LIB_LDFLAGS@
> >>
> >> -libarch_la_SOURCES = features.c
> >> +libarch_la_SOURCES = features.c sigreturn.c
> >>
> >>  libarch_la_CPPFLAGS =                       \
> >>      @XENO_COBALT_CFLAGS@            \
> >> diff --git a/lib/cobalt/arch/x86/sigreturn.c b/lib/cobalt/arch/x86/sigreturn.c
> >> new file mode 100644
> >> index 000000000..76292e145
> >> --- /dev/null
> >> +++ b/lib/cobalt/arch/x86/sigreturn.c
> >> @@ -0,0 +1,32 @@
> >> +#include <cobalt/uapi/syscall.h>
> >> +#include "internal.h"
> >> +
> >> +extern void cobalt_sigreturn (void) asm ("__cobalt_sigreturn") __attribute__
> >> ((visibility ("hidden")));
> >> +
> >> +#ifdef __x86_64__
> >> +#define build_restorer(syscall_number)                                         \
> >> +    asm(".text\n"                                                          \
> >> +        "    .align 16\n"                                                  \
> >> +        "__cobalt_sigreturn:\n"                                            \
> >> +        "    movq $ " #syscall_number ", %rax\n"                           \
> >> +        "    syscall")
> >> +#endif
> >> +
> >> +#ifdef __i386__
> >> +#define build_restorer(syscall_number)                                         \
> >> +    asm(".text\n"                                                          \
> >> +        "    .align 16\n"                                                  \
> >> +        "__cobalt_sigreturn:\n"                                            \
> >> +        "    movl $ " #syscall_number ", %eax\n"                           \
> >> +        "    int  $0x80")
> >> +#endif
> >> +
> >> +/*
> >> + * __COBALT_SYSCALL_BIT | sc_cobalt_sigreturn
> >> + */
> >> +build_restorer(0x10000078);
> >> +
> >> +void *cobalt_get_restorer(void)
> >> +{
> >> +    return &cobalt_sigreturn;
> >> +}
> >> diff --git a/lib/cobalt/internal.h b/lib/cobalt/internal.h
> >> index acb3989f1..4782d154a 100644
> >> --- a/lib/cobalt/internal.h
> >> +++ b/lib/cobalt/internal.h
> >> @@ -132,4 +132,6 @@ static inline bool cobalt_features_available(unsigned
> int
> >> feat_mask)
> >>      return (cobalt_features & feat_mask) == feat_mask;
> >>  }
> >>
> >> +extern void *cobalt_get_restorer(void);
> >> +
> >>  #endif /* _LIB_COBALT_INTERNAL_H */
> >> diff --git a/lib/cobalt/signal.c b/lib/cobalt/signal.c
> >> index 40d315ebb..af174d570 100644
> >> --- a/lib/cobalt/signal.c
> >> +++ b/lib/cobalt/signal.c
> >> @@ -126,3 +126,16 @@ COBALT_IMPL(int, sigqueue, (pid_t pid, int sig, const
> >> union sigval value))
> >>
> >>      return 0;
> >>  }
> >> +
> >> +int cobalt_rt_signal(int sig, void (*handler)(int, siginfo_t *, void *))
> >> +{
> >> +    int ret;
> >> +
> >> +    ret = XENOMAI_SYSCALL3(sc_cobalt_sigaction, sig, handler,
> >> cobalt_get_restorer());
> >> +    if (ret) {
> >> +            errno = -ret;
> >> +            return -1;
> >> +    }
> >> +
> >> +    return 0;
> >> +}
> >> --
> >> 2.25.1
> >
> 
> --
> Siemens AG, Technology
> Competence Center Embedded Linux