The branch main has been updated by trasz:

URL: 
https://cgit.FreeBSD.org/src/commit/?id=ccc510b46340da563e21549a1a0cb99915d8d623

commit ccc510b46340da563e21549a1a0cb99915d8d623
Author:     Edward Tomasz Napierala <tr...@freebsd.org>
AuthorDate: 2021-07-25 06:22:47 +0000
Commit:     Edward Tomasz Napierala <tr...@freebsd.org>
CommitDate: 2021-07-25 06:22:57 +0000

    linux: implement signal delivery on arm64
    
    Note that this still uses FreeBSD-style sigframe;
    this will be addressed later.
    
    Reviewed By:    dchagin
    Sponsored By:   EPSRC
    Differential Revision:  https://reviews.freebsd.org/D31258
---
 sys/arm64/linux/linux.h          | 10 ++++
 sys/arm64/linux/linux_locore.asm |  4 +-
 sys/arm64/linux/linux_sysvec.c   | 98 ++++++++++++++++++++++++++++++++++++++--
 3 files changed, 106 insertions(+), 6 deletions(-)

diff --git a/sys/arm64/linux/linux.h b/sys/arm64/linux/linux.h
index ab3bab8264f4..7ea169b962b4 100644
--- a/sys/arm64/linux/linux.h
+++ b/sys/arm64/linux/linux.h
@@ -243,6 +243,16 @@ typedef struct l_siginfo {
 #define        lsi_band        _sifields._sigpoll._band
 #define        lsi_fd          _sifields._sigpoll._fd
 
+/*
+ * This structure is different from the one used by Linux,
+ * but it doesn't matter - it's not user-accessible.  We need
+ * it instead of the native one because of l_siginfo.
+ */
+struct l_sigframe {
+       struct l_siginfo        sf_si;
+       ucontext_t              sf_uc;
+};
+
 union l_semun {
        l_int           val;
        l_uintptr_t     buf;
diff --git a/sys/arm64/linux/linux_locore.asm b/sys/arm64/linux/linux_locore.asm
index 24a48d74f7b5..0311c2e7e7e9 100644
--- a/sys/arm64/linux/linux_locore.asm
+++ b/sys/arm64/linux/linux_locore.asm
@@ -44,7 +44,9 @@ linux_platform:
 
        .text
 
+       nop     /* This is what Linux calls a "Mysterious NOP". */
 ENTRY(__kernel_rt_sigreturn)
-       brk #0 /* LINUXTODO: implement __kernel_rt_sigreturn */
+       mov     x8, #LINUX_SYS_linux_rt_sigreturn
+       svc     #0
        ret
 END(__kernel_rt_sigreturn)
diff --git a/sys/arm64/linux/linux_sysvec.c b/sys/arm64/linux/linux_sysvec.c
index 72621b4bbfbd..3625155111f2 100644
--- a/sys/arm64/linux/linux_sysvec.c
+++ b/sys/arm64/linux/linux_sysvec.c
@@ -37,12 +37,14 @@ __FBSDID("$FreeBSD$");
 #include <sys/imgact.h>
 #include <sys/imgact_elf.h>
 #include <sys/kernel.h>
+#include <sys/ktr.h>
 #include <sys/lock.h>
 #include <sys/module.h>
 #include <sys/mutex.h>
 #include <sys/proc.h>
 #include <sys/stddef.h>
 #include <sys/signalvar.h>
+#include <sys/syscallsubr.h>
 #include <sys/sysctl.h>
 #include <sys/sysent.h>
 
@@ -61,6 +63,7 @@ __FBSDID("$FreeBSD$");
 #include <compat/linux/linux_ioctl.h>
 #include <compat/linux/linux_mib.h>
 #include <compat/linux/linux_misc.h>
+#include <compat/linux/linux_signal.h>
 #include <compat/linux/linux_util.h>
 #include <compat/linux/linux_vdso.h>
 
@@ -407,18 +410,103 @@ linux_exec_setregs(struct thread *td, struct 
image_params *imgp,
 int
 linux_rt_sigreturn(struct thread *td, struct linux_rt_sigreturn_args *args)
 {
+       struct l_sigframe frame;
+       struct trapframe *tf;
+       int error;
+
+       tf = td->td_frame;
+
+       if (copyin((void *)tf->tf_sp, &frame, sizeof(frame)))
+               return (EFAULT);
 
-       /* LINUXTODO: implement */
-       LIN_SDT_PROBE0(sysvec, linux_rt_sigreturn, todo);
-       return (EDOOFUS);
+       error = set_mcontext(td, &frame.sf_uc.uc_mcontext);
+       if (error != 0)
+               return (error);
+
+       /* Restore signal mask. */
+       kern_sigprocmask(td, SIG_SETMASK, &frame.sf_uc.uc_sigmask, NULL, 0);
+
+       return (EJUSTRETURN);
 }
 
 static void
 linux_rt_sendsig(sig_t catcher, ksiginfo_t *ksi, sigset_t *mask)
 {
+       struct thread *td;
+       struct proc *p;
+       struct trapframe *tf;
+       struct l_sigframe *fp, frame;
+       struct sigacts *psp;
+       int onstack, sig;
+       uint32_t spsr;
+
+       td = curthread;
+       p = td->td_proc;
+       PROC_LOCK_ASSERT(p, MA_OWNED);
+
+       sig = ksi->ksi_signo;
+       psp = p->p_sigacts;
+       mtx_assert(&psp->ps_mtx, MA_OWNED);
+
+       tf = td->td_frame;
+       onstack = sigonstack(tf->tf_sp);
+
+       CTR4(KTR_SIG, "sendsig: td=%p (%s) catcher=%p sig=%d", td, p->p_comm,
+           catcher, sig);
+
+       /* Allocate and validate space for the signal handler context. */
+       if ((td->td_pflags & TDP_ALTSTACK) != 0 && !onstack &&
+           SIGISMEMBER(psp->ps_sigonstack, sig)) {
+               fp = (struct l_sigframe *)((uintptr_t)td->td_sigstk.ss_sp +
+                   td->td_sigstk.ss_size);
+#if defined(COMPAT_43)
+               td->td_sigstk.ss_flags |= SS_ONSTACK;
+#endif
+       } else {
+               fp = (struct l_sigframe *)td->td_frame->tf_sp;
+       }
+
+       /* Make room, keeping the stack aligned */
+       fp--;
+       fp = (struct l_sigframe *)STACKALIGN(fp);
+
+       /* Fill in the frame to copy out */
+       bzero(&frame, sizeof(frame));
+       get_mcontext(td, &frame.sf_uc.uc_mcontext, 0);
+       spsr = frame.sf_uc.uc_mcontext.mc_gpregs.gp_spsr;
+
+       /* Translate the signal. */
+       sig = bsd_to_linux_signal(sig);
+
+       siginfo_to_lsiginfo(&ksi->ksi_info, &frame.sf_si, sig);
+       frame.sf_uc.uc_sigmask = *mask;
+       frame.sf_uc.uc_stack = td->td_sigstk;
+       frame.sf_uc.uc_stack.ss_flags = (td->td_pflags & TDP_ALTSTACK) != 0 ?
+           (onstack ? SS_ONSTACK : 0) : SS_DISABLE;
+       mtx_unlock(&psp->ps_mtx);
+       PROC_UNLOCK(td->td_proc);
+
+       /* Copy the sigframe out to the user's stack. */
+       if (copyout(&frame, fp, sizeof(*fp)) != 0) {
+               /* Process has trashed its stack. Kill it. */
+               CTR2(KTR_SIG, "sendsig: sigexit td=%p fp=%p", td, fp);
+               PROC_LOCK(p);
+               sigexit(td, SIGILL);
+       }
+
+       tf->tf_x[0]= sig;
+       tf->tf_x[1] = (register_t)&fp->sf_si;
+       tf->tf_x[2] = (register_t)&fp->sf_uc;
+
+       tf->tf_elr = (register_t)catcher;
+       tf->tf_sp = (register_t)fp;
+       tf->tf_lr = (register_t)__kernel_rt_sigreturn;
+
+       CTR3(KTR_SIG, "sendsig: return td=%p pc=%#x sp=%#x", td, tf->tf_elr,
+           tf->tf_sp);
 
-       /* LINUXTODO: implement */
-       LIN_SDT_PROBE0(sysvec, linux_rt_sendsig, todo);
+       PROC_LOCK(p);
+       mtx_lock(&psp->ps_mtx);
 }
 
 struct sysentvec elf_linux_sysvec = {
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