Re: [LTP] [PATCH] syscall02: add invalid syscall number test

[Petr Vorel <pvorel@suse.cz>]

Hi Andrea, Wei,

> > Add a test verifying that syscall() returns ENOSYS when called with
> > unimplemented syscall numbers. The chosen numbers stay above the syscall
> > table and below the architecture-specific private ranges, so they are
> > reliably invalid on every supported architecture.

+1

Reviewed-by: Petr Vorel <pvorel@suse.cz>

...
> > +++ b/testcases/kernel/syscalls/syscall/syscall02.c
> > @@ -0,0 +1,47 @@
> > +// SPDX-License-Identifier: GPL-2.0-or-later
> > +/*
> > + * Copyright (c) 2026 Andrea Cervesato <andrea.cervesato@suse.com>
> > + */
> > +
> > +/*\
> > + * Verify that :manpage:`syscall(2)` fails with ENOSYS when invoked with
> > + * invalid syscall numbers.
> > + *
> > + * The syscall number is dispatched as an unsigned value on Linux. A value is
> > + * reliably unimplemented on every supported architecture when it is:
> > + *
> > + * - above the syscall table
> > + * - below the architecture-specific private syscall ranges (e.g. ARM's
> > + *   0x0f0000 base)
> > + * - without the x32 ABI bit (0x40000000) set
> > + *
> > + * Such a number is routed to sys_ni_syscall and returns ENOSYS.
> > + */
> > +
> > +#include <unistd.h>
> > +#include <sys/syscall.h>
> > +
> > +#include "tst_test.h"
> > +
> > +#define TC(x) {.scno = (long)(x), .desc = #x}
> > +
> > +static struct tcase {
> > +	long scno;
> > +	const char *desc;
> > +} tcases[] = {
> > +	TC(0x8000),
> > +	TC(0xf000),
> > +	TC(0xfffe),
> > +};

> I suggest add two more cases check:
> 1) -1
> 2) __NR_syscalls +1 (Base arch/powerpc/kernel/syscall.c)

+1. Something like this wouldn't harm (tested only on x86_64 and x86).

Kind regards,
Petr

+++ testcases/kernel/syscalls/syscall/syscall02.c
@@ -14,12 +14,15 @@
  * - below the architecture-specific private syscall ranges (e.g. ARM's
  *   0x0f0000 base)
  * - without the x32 ABI bit (0x40000000) set
+ * - -1
+ * - __NR_syscalls + 1
  *
  * Such a number is routed to sys_ni_syscall and returns ENOSYS.
  */
 
 #include <unistd.h>
 #include <sys/syscall.h>
+#include <asm-generic/unistd.h>
 
 #include "tst_test.h"
 
@@ -32,6 +35,8 @@ static struct tcase {
 	TC(0x8000),
 	TC(0xf000),
 	TC(0xfffe),
+	TC(-1),
+	TC(__NR_syscalls + 1),
 };
 
 static void verify_syscall(unsigned int n)

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