From 53186bc1435e2c3ccf9c2124c066a08c6a80c504 Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Fri, 19 Apr 2024 17:29:05 +0300
Subject: [PATCH] sigqueue(2): add impl-specific flag __SIGQUEUE_TID

The flag allows the pid argument to designate a thread from the calling
process.  The flag value is carved from the high bit of the signal
number, which slightly changes the ABI of syscall.

Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D44867
---
 sys/kern/kern_sig.c | 22 +++++++++++++++++-----
 sys/sys/signal.h    |  4 ++++
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index a533460090eb..7ac9dcb8cb40 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -2012,13 +2012,16 @@ sys_sigqueue(struct thread *td, struct sigqueue_args *uap)
 }
 
 int
-kern_sigqueue(struct thread *td, pid_t pid, int signum, union sigval *value)
+kern_sigqueue(struct thread *td, pid_t pid, int signumf, union sigval *value)
 {
 	ksiginfo_t ksi;
 	struct proc *p;
+	struct thread *td2;
+	u_int signum;
 	int error;
 
-	if ((u_int)signum > _SIG_MAXSIG)
+	signum = signumf & ~__SIGQUEUE_TID;
+	if (signum > _SIG_MAXSIG)
 		return (EINVAL);
 
 	/*
@@ -2028,8 +2031,17 @@ kern_sigqueue(struct thread *td, pid_t pid, int signum, union sigval *value)
 	if (pid <= 0)
 		return (EINVAL);
 
-	if ((p = pfind_any(pid)) == NULL)
-		return (ESRCH);
+	if ((signumf & __SIGQUEUE_TID) == 0) {
+		if ((p = pfind_any(pid)) == NULL)
+			return (ESRCH);
+		td2 = NULL;
+	} else {
+		p = td->td_proc;
+		td2 = tdfind((lwpid_t)pid, p->p_pid);
+		if (td2 == NULL)
+			return (ESRCH);
+	}
+
 	error = p_cansignal(td, p, signum);
 	if (error == 0 && signum != 0) {
 		ksiginfo_init(&ksi);
@@ -2039,7 +2051,7 @@ kern_sigqueue(struct thread *td, pid_t pid, int signum, union sigval *value)
 		ksi.ksi_pid = td->td_proc->p_pid;
 		ksi.ksi_uid = td->td_ucred->cr_ruid;
 		ksi.ksi_value = *value;
-		error = pksignal(p, ksi.ksi_signo, &ksi);
+		error = tdsendsignal(p, td2, ksi.ksi_signo, &ksi);
 	}
 	PROC_UNLOCK(p);
 	return (error);
diff --git a/sys/sys/signal.h b/sys/sys/signal.h
index 068a7e7bc6da..690cab414e9e 100644
--- a/sys/sys/signal.h
+++ b/sys/sys/signal.h
@@ -475,6 +475,10 @@ struct sigstack {
 
 #if __BSD_VISIBLE
 #define	BADSIG		SIG_ERR
+
+/* sigqueue(2) signo high-bits flags */
+#define	__SIGQUEUE_TID	0x80000000	/* queue for tid, instead of pid */
+#define	__SIGQUEUE_RSRV	0x40000000	/* reserved */
 #endif
 
 #if __POSIX_VISIBLE || __XSI_VISIBLE