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

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

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. 

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.

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