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

[Jan Kiszka <jan.kiszka@siemens.com>]

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.

> +{
> +	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).

We will also need pagefault_disable in our dovetail functions, already 
playing with that.

> +	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.

Jan

-- 
Siemens AG, Technology
Linux Expert Center