[LTP] [PATCH 2/4] syscalls/modify_ldt: Refactor modify_ldt03 into new API

[Andrea Cervesato]

Hi!

This test is actually a bit simple. According to man pages:

        When func is 0, modify_ldt() reads the LDT into the memory pointed
        to by ptr.  The number of bytes read is the smaller of bytecount
        and the actual size of the LDT, although the kernel may act as
        though the LDT is padded with additional trailing zero bytes.  On
        success, modify_ldt() will return the number of bytes read.

So we should verify that by reading the LDT we are able to obtain data 
from modify_ldt() syscall.

More comments below.

On 3/24/25 21:45, Ricardo B. Marliere via ltp wrote:
> From: Ricardo B. Marlière <rbm@suse.com>
>
> Signed-off-by: Ricardo B. Marlière <rbm@suse.com>
> ---
>   .../kernel/syscalls/modify_ldt/modify_ldt03.c      | 114 ++++-----------------
>   1 file changed, 20 insertions(+), 94 deletions(-)
>
> diff --git a/testcases/kernel/syscalls/modify_ldt/modify_ldt03.c b/testcases/kernel/syscalls/modify_ldt/modify_ldt03.c
> index 01730e0e14ae98a934e7b66c9058454506bbe064..6ecfa1e9f987a6fc349e551b4f0e175d14e62642 100644
> --- a/testcases/kernel/syscalls/modify_ldt/modify_ldt03.c
> +++ b/testcases/kernel/syscalls/modify_ldt/modify_ldt03.c
> @@ -1,105 +1,31 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +
>   /*
> - * Copyright (c) 2014 Fujitsu Ltd.
> - * Author: Zeng Linggang <zenglg.jy@cn.fujitsu.com>
> - *
> - * This program is free software; you can redistribute it and/or modify it
> - * under the terms of version 2 of the GNU General Public License as
> - * published by the Free Software Foundation.
> - *
> - * This program is distributed in the hope that it would be useful, but
> - * WITHOUT ANY WARRANTY; without even the implied warranty of
> - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
> - *
> - * You should have received a copy of the GNU General Public License along
> - * with this program.
> - */
> -/*
> - * DESCRIPTION
> - *	Basic test for modify_ldt(2) using func=0 argument.
> + * Copyright (c) 2014 Fujitsu Ltd. Zeng Linggang <zenglg.jy@cn.fujitsu.com>
> + * Copyright (c) 2025 SUSE LLC Ricardo B. Marlière <rbm@suse.com>
>    */
>   
> -#include "config.h"
> -#include "test.h"
> -
> -char *TCID = "modify_ldt03";
> -int TST_TOTAL = 1;
> -
> -#if defined(__i386__) && defined(HAVE_MODIFY_LDT)
> -
> -#ifdef HAVE_ASM_LDT_H
> -# include <asm/ldt.h>
> -#endif
> -extern int modify_ldt(int, void *, unsigned long);
> -
> -#include <asm/unistd.h>
> -#include <string.h>
> -#include <sys/wait.h>
> -#include <errno.h>
> -#include "safe_macros.h"
> -
> -#ifdef HAVE_STRUCT_USER_DESC
> -# define SIZE sizeof(struct user_desc)
> -#else
> -# define SIZE 16
> -#endif
> -
> -static char buf[SIZE];
> -static void cleanup(void);
> -static void setup(void);
> -
> -int main(int ac, char **av)
> -{
> -	int lc;
> -
> -	tst_parse_opts(ac, av, NULL, NULL);
> -
> -	setup();
> -
> -	for (lc = 0; TEST_LOOPING(lc); lc++) {
> -
> -		tst_count = 0;
> -
> -		TEST(modify_ldt(0, buf, SIZE));
> +/*\
> + * Verify that a simple read (func=0) works when calling modify_ldt.
> + */
>   
> -		if (TEST_RETURN < 0) {
> -			tst_resm(TFAIL | TTERRNO,
> -				 "modify_ldt() failed with errno: %s",
> -				 strerror(TEST_ERRNO));
> -		} else {
> -			tst_resm(TPASS, "modify_ldt() tested success");
> -		}
> -	}
> +#include "tst_test.h"
>   
> -	cleanup();
> -	tst_exit();
> -}
> +#ifdef __i386__
> +#include "lapi/ldt.h"
>   
> -static void setup(void)
> +void run(void)
>   {
> -	tst_sig(NOFORK, DEF_HANDLER, cleanup);
> +	char buf[sizeof(struct user_desc)];
Not a good idea to initialize structs in this way, since their dimension 
might change with time.
We should use a guarded buffer and to clean it before using it.
>   
> -	TEST_PAUSE;
> +	TEST(modify_ldt(0, buf, sizeof(buf)));
We can go straight using TST_EXP_EQ_LI()
> +	TST_EXP_EQ_LI(TST_RET, 0);
>   }
>   
> -static void cleanup(void)
> -{
> -}
> +static struct tst_test test = {
> +	.test_all = run,
> +};
>   
> -#elif HAVE_MODIFY_LDT
> -
> -int main(void)
> -{
> -	tst_brkm(TCONF,
> -		 NULL, "modify_ldt is available but not tested on the platform than "
> -		 "__i386__");
> -}
> -
> -#else /* if defined(__i386__) */
> -
> -int main(void)
> -{
> -	tst_resm(TINFO, "modify_ldt03 test only for ix86");
> -	tst_exit();
> -}
> -
> -#endif /* if defined(__i386__) */
> +#else
> +TST_TEST_TCONF("Test supported only on i386");
This test is probably supported by x86_64 as well.
> +#endif /* __i386__ */
>
Kind regards,
Andrea Cervesato