On Tue, Jul 07, 2026 at 09:07:09PM +0200, Thomas Gleixner wrote:

From: Michal Suchánek <redacted>

The return values of syscall_enter_from_user_mode[_work]() are
non-intuitive. Both functions return the syscall number which should be
invoked by the architecture specific syscall entry code. The returned
number can be:

  - the unmodified syscall number which was handed in by the caller

  - a modified syscall number (ptrace, seccomp, trace/probe/bpf)

That has an additional twist. If the return value is -1L then the caller is
not allowed to modify the return value as that indicates that the modifying
entity requests to abort the syscall and set the return value already. That
can obviously not be differentiated from a syscall which handed in -1 as
syscall number.

The established way to deal with that is:

    set_return_value(regs, -ENOSYS);
    nr = syscall_enter_from_user_mode(regs, nr);
    if ((unsigned)nr < SYSCALLNR_MAX)
    	handle_syscall(regs, nr);
    else if (nr != -1)
    	set_return_value(regs, -ENOSYS);

The latter is obviously redundant, but that's just a leftover of the
historical evolution of this code. S390 has some special requirements here,
which can be avoided when the return value is not ambiguous.

Now that the functions which modify the syscall number and want to abort
are converted to indicate that with a boolean return value, it's obvious to
hand this through to the callers.

Rework syscall_enter_from_user_mode[_work]) so they take a pointer to the
syscall number and return a boolean, which indicates whether the syscall
should be handled or not.

That's not only more intuitive, it also results in slightly denser
executable code on x86 at least, but perf results are neutral and within
the noise.

[ tglx: Adopted it to the changes in the generic entry code, fixed up the
  	32-bit fallout and rewrote change log ]

Signed-off-by: Michal Suchánek <redacted>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Shrikanth Hegde <redacted>
Cc: Paul Walmsley <pjw@kernel.org>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: linux-doc@vger.kernel.org
Cc: loongarch@lists.linux.dev
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-riscv@lists.infradead.org
Cc: linux-s390@vger.kernel.org
---
 Documentation/core-api/entry.rst |   18 +++++++++++-------
 arch/loongarch/kernel/syscall.c  |   14 +++++++-------
 arch/powerpc/kernel/syscall.c    |    3 ++-
 arch/riscv/kernel/traps.c        |   11 +++++------
 arch/s390/kernel/syscall.c       |    7 +++++--
 arch/x86/entry/syscall_32.c      |   25 ++++++++++++-------------
 arch/x86/entry/syscall_64.c      |   12 ++++++------
 include/linux/entry-common.h     |   12 +++++-------
 8 files changed, 53 insertions(+), 49 deletions(-)

 

[...]

Missing one closing ')'.

+		return syscall_get_error(current, regs);
 
 	if (unlikely(r0 >= NR_syscalls)) {
 		if (unlikely(trap_is_unsupported_scv(regs))) {

Apart from this.


Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <redacted>