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

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

Hi Jan,

> -----Original Message-----
> From: Jan Kiszka <jan.kiszka@siemens.com>
> Sent: Freitag, 1. September 2023 14:00
> To: Johannes Kirchmair <johannes.kirchmair@sigmatek.at>;
> xenomai@lists.linux.dev
> Subject: Re: [PATCH 1/3] [POC] test implementaion of rt-signals
> 
> CAUTION: External E-Mail !
> 
> On 16.08.23 12:18, Johannes Kirchmair wrote:
> > 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/signal.h                  |  1 +
> >  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          | 37 +++++++++
> >  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               | 36 +++++++++
> >  lib/cobalt/internal.h                         |  2 +
> >  lib/cobalt/signal.c                           | 13 ++++
> >  18 files changed, 282 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/signal.h b/include/cobalt/uapi/signal.h
> > index 8a7ea15a4..1afb6050a 100644
> > --- a/include/cobalt/uapi/signal.h
> > +++ b/include/cobalt/uapi/signal.h
> > @@ -68,6 +68,7 @@
> >  #define SIGDEBUG_RESCNT_IMBALANCE    7
> >  #define SIGDEBUG_LOCK_BREAK          8
> >  #define SIGDEBUG_MUTEX_SLEEP         9
> > +#define SIGDEBUG_SIGRESTOR           10
> >
> >  #define COBALT_DELAYMAX                      2147483647U
> >
> > diff --git a/include/cobalt/uapi/syscall.h b/include/cobalt/uapi/syscall.h
> > index 3e65efaab..f14bd8ffe 100644
> > --- a/include/cobalt/uapi/syscall.h
> > +++ b/include/cobalt/uapi/syscall.h
> > @@ -142,6 +142,12 @@
> >  #define sc_cobalt_timerfd_gettime64          119
> >  #define sc_cobalt_pselect64                  120
> >
> > +/*
> > + * Sigmatek specific syscalls
> > + */
> > +#define sc_cobalt_sigreturn                  121
> > +#define sc_cobalt_sigaction                  122
> > +
> >  #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..140016460
> > --- /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)
> 
> Why is this function in file that suggests to handle only 32-bit? It's
> shared by both 32 and 64 bit.
Did not changed it yet?
Should I add an distinct signal.c file for the function?

> 
> > +{
> > +     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(), SIGDEBUG_SIGRESTOR);
> > +     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..3b8cd3330
> > --- /dev/null
> > +++ b/kernel/cobalt/arch/x86/signal_ia64.c
> > @@ -0,0 +1,37 @@
> > +// 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)
> > +{
> > +     int ret;
> > +
> > +     ret = dovetail_restore_rt_signal_frame(regs);
> > +     if (ret < 0)
> > +             goto badframe;
> > +
> > +     return regs->ax;
> > +
> > +badframe:
> > +     xnthread_call_mayday(xnthread_current(), SIGDEBUG_SIGRESTOR);
> 
> I'm not sure if this is the right way to react. Mayday will translate to
> SIGDEBUG, but we need a SIGSEGV.
> 
> > +     return -1;
> > +
> > +}
> > +
> > 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;
> 
> Unrelated and unneeded change.
> 
> >  }
> >
> >  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
> 
> Unrelated and bogus change.
> 
> >       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 780d276b1..7c858f904 100644
> > --- a/kernel/cobalt/posix/syscall32.c
> > +++ b/kernel/cobalt/posix/syscall32.c
> > @@ -705,6 +705,22 @@ 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);
> 
> All this is called with interrupts off on x86, and that makes dovetail
> unhappy:
> 
> [   17.051995] 9pnet: Limiting 'msize' to 512000 as this is the maximum supported
> by transport virtio
> [   37.268218] ------------[ cut here ]------------
> [   37.268223] WARNING: CPU: 2 PID: 1402 at ../mm/memory.c:5857
> __might_fault+0x95/0xa0
> [   37.268237] Modules linked in: 9p netfs rt_e1000 rt_e1000_new rtnet
> [   37.268252] CPU: 2 PID: 1402 Comm: rt-task Not tainted 6.5.0+ #40
> [   37.268259] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-
> 1.16.0-0-gd239552c-rebuilt.opensuse.org 04/01/2014
> [   37.268262] IRQ stage: Xenomai
> [   37.268265] RIP: 0010:__might_fault+0x95/0xa0
> [   37.268271] Code: b8 a0 01 00 00 e8 cb bf e3 ff 48 8b bb e8 04 00 00 48 8b 5d
> f8 48 c7 c6 6b 29 2d 81 58 c9 48 81 c7 a0 01 00 00 e9 2b bc e3 ff <0f> 0b eb 86
> 0f 1f 80 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90
> [   37.268277] RSP: 0000:ffffc900007f3cd0 EFLAGS: 00010046
> [   37.268283] RAX: 0000000000000006 RBX: 00007f5aa94016b8 RCX:
> ffffc900007f3d70
> [   37.268287] RDX: 00007f5aa9401cc4 RSI: 00000000000000a7 RDI:
> ffffffff82962a10
> [   37.268291] RBP: ffffc900007f3cd8 R08: 0000000000000444 R09:
> 0000000000000000
> [   37.268295] R10: 0000000000000000 R11: 0000000000000000 R12:
> 0000000000000000
> [   37.268298] R13: ffff888009e6e700 R14: 0000000000000000 R15:
> 00000000000299a0
> [   37.268302] FS:  00007f5aa9402700(0000) GS:ffff88803ed00000(0000)
> knlGS:0000000000000000
> [   37.268313] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   37.268317] CR2: 0000560ba8044008 CR3: 000000000981a004 CR4:
> 0000000000370ee0
> [   37.268321] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> 0000000000000000
> [   37.268324] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
> 0000000000000400
> [   37.268328] Call Trace:
> [   37.268332]  <TASK>
> [   37.268339]  ? __warn+0x81/0x180
> [   37.268350]  ? __might_fault+0x95/0xa0
> [   37.268363]  ? report_bug+0x10b/0x200
> [   37.268406]  ? handle_bug+0x50/0xc0
> [   37.268417]  ? exc_invalid_op+0xc7/0xe0
> [   37.268427]  ? asm_exc_invalid_op+0x16/0x20
> [   37.268467]  ? __might_fault+0x95/0xa0
> [   37.268485]  copy_fpstate_to_sigframe+0x74/0x430
> [   37.268496]  ? ___xnsched_run+0x223/0x590
> [   37.268515]  ? __pfx____xnsched_run+0x10/0x10
> [   37.268541]  get_sigframe+0xea/0x2b0
> [   37.268562]  x64_setup_rt_frame+0x68/0x2f0
> [   37.268583]  xnthread_handle_rt_signals+0xf8/0x130
> [   37.268633]  handle_oob_trap_entry+0xaa/0x3a0
> [   37.268640]  ? __pfx_CoBaLt_sigaction+0x10/0x10
> [   37.268666]  __oob_trap_notify+0x27/0x30
> [   37.268674]  do_error_trap+0x162/0x1d0
> [   37.268695]  exc_divide_error+0x35/0x50
> [   37.268707]  asm_exc_divide_error+0x16/0x20
> [   37.268713] RIP: 0033:0x400e68
> 
> I'm currently scratching my head if we can safely enable hard interrupts
> here to resolve this (and the underlying latency source).
Not sure what is the right way. Have some problems understanding, what has to be protected for the setup to work correct.

> 
> We will also need pagefault_disable in our dovetail functions, already
> playing with that.
Could you explain to me, what pagefault_disable does and by we need it.

> 
> > +     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..df961469e
> > --- /dev/null
> > +++ b/lib/cobalt/arch/x86/sigreturn.c
> > @@ -0,0 +1,36 @@
> > +#include <cobalt/uapi/syscall.h>
> > +#include "internal.h"
> > +
> > +extern void cobalt_sigreturn (void) asm ("__cobalt_sigreturn") __attribute__
> ((visibility ("hidden")));
> > +
> > +#define TO_STR(x) #x
> > +
> > +#ifdef __x86_64__
> > +#define build_restorer(syscall_bit, syscall)                                   \
> > +     asm(".text\n"                                                          \
> > +         "    .align 16\n"                                                  \
> > +         "__cobalt_sigreturn:\n"                                            \
> > +         "    movq $ " TO_STR(syscall_bit) ", %rax\n"                       \
> > +         "    orq $ " TO_STR(syscall) ", %rax\n"                            \
> > +         "    syscall")
> > +#endif
> > +
> > +#ifdef __i386__
> > +#define build_restorer(syscall_bit, syscall)                                   \
> > +     asm(".text\n"                                                          \
> > +         "    .align 16\n"                                                  \
> > +         "__cobalt_sigreturn:\n"                                            \
> > +         "    movl $ " TO_STR(syscall_bit) ", %eax\n"                       \
> > +         "    orl $ " TO_STR(syscall) ", %eax\n"                            \
> > +         "    int  $0x80")
> > +#endif
> > +
> > +/*
> > + * __COBALT_SYSCALL_BIT | sc_cobalt_sigreturn
> > + */
> > +build_restorer(__COBALT_SYSCALL_BIT, sc_cobalt_sigreturn);
> > +
> > +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;
> > +}
> 
> IOW: I started hacking as well, based on latest 6.5 and xenomai next.
> More to come.
That’s good, actually notice more and more, that my knowledge of the kernel is to limited to tackle this signal implementation.

Best regards 
Johannes
> 
> Jan
> 
> --
> Siemens AG, Technology
> Linux Expert Center