syscall.h: introduce syscall_set_nr()

Similar to syscall_set_arguments() that complements
syscall_get_arguments(), introduce syscall_set_nr() that complements
syscall_get_nr().

syscall_set_nr() is going to be needed along with syscall_set_arguments()
on all HAVE_ARCH_TRACEHOOK architectures to implement
PTRACE_SET_SYSCALL_INFO API.

Link: https://lkml.kernel.org/r/20250303112020.GD24170@strace.io
Signed-off-by: Dmitry V. Levin <ldv@strace.io>
Tested-by: Charlie Jenkins <charlie@rivosinc.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Acked-by: Helge Deller <deller@gmx.de> # parisc
Reviewed-by: Maciej W. Rozycki <macro@orcam.me.uk> # mips
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alexey Gladkov (Intel) <legion@kernel.org>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: anton ivanov <anton.ivanov@cambridgegreys.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Brian Cain <bcain@quicinc.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christian Zankel <chris@zankel.net>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Davide Berardi <berardi.dav@gmail.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Eugene Syromiatnikov <esyr@redhat.com>
Cc: Eugene Syromyatnikov <evgsyr@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Guo Ren <guoren@kernel.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Naveen N Rao <naveen@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Renzo Davoi <renzo@cs.unibo.it>
Cc: Richard Weinberger <richard@nod.at>
Cc: Rich Felker <dalias@libc.org>
Cc: Russel King <linux@armlinux.org.uk>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Stafford Horne <shorne@gmail.com>
Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vineet Gupta <vgupta@kernel.org>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Will Deacon <will@kernel.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/arc/include/asm/syscall.h

@@ -23,6 +23,17 @@ syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 		return -1;
 }
 
+static inline void
+syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
+{
+	/*
+	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
+	 * the target task is stopped for tracing on entering syscall, so
+	 * there is no need to have the same check syscall_get_nr() has.
+	 */
+	regs->r8 = nr;
+}
+
 static inline void
 syscall_rollback(struct task_struct *task, struct pt_regs *regs)
 {

arch/arm/include/asm/syscall.h

@@ -68,6 +68,30 @@ static inline void syscall_set_return_value(struct task_struct *task,
 	regs->ARM_r0 = (long) error ? error : val;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	if (nr == -1) {
+		task_thread_info(task)->abi_syscall = -1;
+		/*
+		 * When the syscall number is set to -1, the syscall will be
+		 * skipped.  In this case the syscall return value has to be
+		 * set explicitly, otherwise the first syscall argument is
+		 * returned as the syscall return value.
+		 */
+		syscall_set_return_value(task, regs, -ENOSYS, 0);
+		return;
+	}
+	if ((IS_ENABLED(CONFIG_AEABI) && !IS_ENABLED(CONFIG_OABI_COMPAT))) {
+		task_thread_info(task)->abi_syscall = nr;
+		return;
+	}
+	task_thread_info(task)->abi_syscall =
+		(task_thread_info(task)->abi_syscall & ~__NR_SYSCALL_MASK) |
+		(nr & __NR_SYSCALL_MASK);
+}
+
 #define SYSCALL_MAX_ARGS 7
 
 static inline void syscall_get_arguments(struct task_struct *task,

arch/arm64/include/asm/syscall.h

@@ -61,6 +61,22 @@ static inline void syscall_set_return_value(struct task_struct *task,
 	regs->regs[0] = val;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->syscallno = nr;
+	if (nr == -1) {
+		/*
+		 * When the syscall number is set to -1, the syscall will be
+		 * skipped.  In this case the syscall return value has to be
+		 * set explicitly, otherwise the first syscall argument is
+		 * returned as the syscall return value.
+		 */
+		syscall_set_return_value(task, regs, -ENOSYS, 0);
+	}
+}
+
 #define SYSCALL_MAX_ARGS 6
 
 static inline void syscall_get_arguments(struct task_struct *task,

arch/hexagon/include/asm/syscall.h

@@ -26,6 +26,13 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return regs->r06;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->r06 = nr;
+}
+
 static inline void syscall_get_arguments(struct task_struct *task,
 					 struct pt_regs *regs,
 					 unsigned long *args)

arch/loongarch/include/asm/syscall.h

@@ -26,6 +26,13 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return regs->regs[11];
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->regs[11] = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/m68k/include/asm/syscall.h

@@ -14,6 +14,13 @@ static inline int syscall_get_nr(struct task_struct *task,
 	return regs->orig_d0;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->orig_d0 = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/microblaze/include/asm/syscall.h

@@ -14,6 +14,13 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return regs->r12;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->r12 = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/mips/include/asm/syscall.h

@@ -41,6 +41,21 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return task_thread_info(task)->syscall;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	/*
+	 * New syscall number has to be assigned to regs[2] because
+	 * it is loaded from there unconditionally after return from
+	 * syscall_trace_enter() invocation.
+	 *
+	 * Consequently, if the syscall was indirect and nr != __NR_syscall,
+	 * then after this assignment the syscall will cease to be indirect.
+	 */
+	task_thread_info(task)->syscall = regs->regs[2] = nr;
+}
+
 static inline void mips_syscall_update_nr(struct task_struct *task,
 					  struct pt_regs *regs)
 {

arch/nios2/include/asm/syscall.h

@@ -15,6 +15,11 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 	return regs->r2;
 }
 
+static inline void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
+{
+	regs->r2 = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				struct pt_regs *regs)
 {

arch/openrisc/include/asm/syscall.h

@@ -25,6 +25,12 @@ syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 	return regs->orig_gpr11;
 }
 
+static inline void
+syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
+{
+	regs->orig_gpr11 = nr;
+}
+
 static inline void
 syscall_rollback(struct task_struct *task, struct pt_regs *regs)
 {

arch/parisc/include/asm/syscall.h

@@ -17,6 +17,13 @@ static inline long syscall_get_nr(struct task_struct *tsk,
 	return regs->gr[20];
 }
 
+static inline void syscall_set_nr(struct task_struct *tsk,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->gr[20] = nr;
+}
+
 static inline void syscall_get_arguments(struct task_struct *tsk,
 					 struct pt_regs *regs,
 					 unsigned long *args)

arch/powerpc/include/asm/syscall.h

@@ -39,6 +39,16 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 		return -1;
 }
 
+static inline void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
+{
+	/*
+	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
+	 * the target task is stopped for tracing on entering syscall, so
+	 * there is no need to have the same check syscall_get_nr() has.
+	 */
+	regs->gpr[0] = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/riscv/include/asm/syscall.h

@@ -30,6 +30,13 @@ static inline int syscall_get_nr(struct task_struct *task,
 	return regs->a7;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->a7 = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/s390/include/asm/syscall.h

@@ -24,6 +24,18 @@ static inline long syscall_get_nr(struct task_struct *task,
 		(regs->int_code & 0xffff) : -1;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	/*
+	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
+	 * the target task is stopped for tracing on entering syscall, so
+	 * there is no need to have the same check syscall_get_nr() has.
+	 */
+	regs->int_code = (regs->int_code & ~0xffff) | (nr & 0xffff);
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/sh/include/asm/syscall_32.h

@@ -15,6 +15,18 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return (regs->tra >= 0) ? regs->regs[3] : -1L;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	/*
+	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
+	 * the target task is stopped for tracing on entering syscall, so
+	 * there is no need to have the same check syscall_get_nr() has.
+	 */
+	regs->regs[3] = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/sparc/include/asm/syscall.h

@@ -25,6 +25,18 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return (syscall_p ? regs->u_regs[UREG_G1] : -1L);
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	/*
+	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
+	 * the target task is stopped for tracing on entering syscall, so
+	 * there is no need to have the same check syscall_get_nr() has.
+	 */
+	regs->u_regs[UREG_G1] = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/um/include/asm/syscall-generic.h

@@ -21,6 +21,11 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 	return PT_REGS_SYSCALL_NR(regs);
 }
 
+static inline void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
+{
+	PT_REGS_SYSCALL_NR(regs) = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/x86/include/asm/syscall.h

@@ -38,6 +38,13 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 	return regs->orig_ax;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->orig_ax = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/xtensa/include/asm/syscall.h

@@ -28,6 +28,13 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return regs->syscall;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->syscall = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

include/asm-generic/syscall.h

@@ -37,6 +37,20 @@ struct pt_regs;
  */
 int syscall_get_nr(struct task_struct *task, struct pt_regs *regs);
 
+/**
+ * syscall_set_nr - change the system call a task is executing
+ * @task:	task of interest, must be blocked
+ * @regs:	task_pt_regs() of @task
+ * @nr:		system call number
+ *
+ * Changes the system call number @task is about to execute.
+ *
+ * It's only valid to call this when @task is stopped for tracing on
+ * entry to a system call, due to %SYSCALL_WORK_SYSCALL_TRACE or
+ * %SYSCALL_WORK_SYSCALL_AUDIT.
+ */
+void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr);
+
 /**
  * syscall_rollback - roll back registers after an aborted system call
  * @task:	task of interest, must be in system call exit tracing