[PATCH v2] Implement decoding of ustat syscall

[Dmitry V. Levin]

On Fri, Jan 06, 2017 at 10:27:05PM +0800, JingPiao Chen wrote:
[...]
> +#include "defs.h"
> +#include DEF_MPERS_TYPE(struct_ustat)
> +#include <ustat.h>
> +typedef struct ustat struct_ustat;
> +#include MPERS_DEFS

This is correct.

> +
> +SYS_FUNC(ustat)
> +{
> +	struct_ustat ust;
> +
> +	if (entering(tcp))
> +		print_dev_t(tcp->u_arg[0]);

This is not quite correct, because, as you can see

$ git grep sys_ustat include/linux/
include/linux/compat.h:asmlinkage long compat_sys_ustat(unsigned dev, struct compat_ustat __user *u32);
include/linux/syscalls.h:asmlinkage long sys_ustat(unsigned dev, struct ustat __user *ubuf);

the type of 1st argument is unsigned int.
An explicit cast to (unsigned int) is needed.

> +	else {
> +		tprints(", ");
> +		if (!umove_or_printaddr(tcp, tcp->u_arg[1], &ust))
> +			tprintf("{f_tfree=%llu, f_tinode=%llu}",
> +					zero_extend_signed_to_ull(ust.f_tfree),
> +					zero_extend_signed_to_ull(ust.f_tinode));

Please indent properly.

[...]
> +#include "tests.h"
> +#include <asm/unistd.h>
> +
> +#ifdef __NR_ustat
> +
> +#include <stdio.h>
> +#include <unistd.h>
> +#include <ustat.h>
> +
> +int
> +main(void)
> +{
> +	struct ustat ust;

Use tail_alloc to allocate memory for the object at the end of mapped
segment.

> +
> +	long rc = syscall(__NR_ustat, -1, 0);

What is -1 here?  Is it int or long?  Is it going to be sign-extended
or not?  Please be specific when invoking syscall().

I suggest replacing -1 with a magic of type kernel_ulong_t, e.g.
	kernel_ulong_t magic = (kernel_ulong_t) 0xfacefeedffffffff;

> +	printf("ustat(makedev(%u, %u), NULL) = %s\n", major((unsigned int) -1),
> +			minor((unsigned int) -1), sprintrc(rc));

There is a shorter way to write this, e.g. -1U.

> +	rc = syscall(__NR_ustat, -1, &ust);
> +	printf("ustat(makedev(%u, %u), %p) = %s\n", major((unsigned int) -1),
> +			minor((unsigned int) -1), &ust, sprintrc(rc));

Please test the case when ustat succeeds.  For example, find out a real
device number and feed it to ustat.  If this device number doesn't
overflow unsigned int, the syscall is likely to succeed.


-- 
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