On Tue, 03 Sep 2013, nidhi mittal hada wrote:
> Hi,
>
> while in the pursuit of learning to understand assembly ..
> This is my doubt ..Please help to understand
>
> *I want to catch where in this disassembly call is made to get_sb function.*
>
> Somehow in this disassembly, i m not finding, a direct *call* instruction,
> with function name, written in english.
>
> [...]
>
> *Thats the definition of function*
>
> vfs_kern_mount(struct file_system_type *type, int flags, const char *name,
> void *data)
> {
> struct vfsmount *mnt;
> char *secdata = NULL;
> int error;
>
> if (!type)
> return ERR_PTR(-ENODEV);
>
> error = -ENOMEM;
>
> * mnt = alloc_vfsmnt(name);*
> if (!mnt)
> goto out;
>
> *<<<<<<<<<<<<<<THIS PORTION, IS NOT VISIBLE TO ME, **IN ASSEMBLY
> >>>>>>>>>>>>>>>*
> if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {
> secdata = alloc_secdata();
> if (!secdata)
> goto out_mnt;
>
> error = security_sb_copy_data(data, secdata);
> if (error)
> goto out_free_secdata;
> }
>
> * error = type->get_sb(type, flags, name, data,
> mnt);>>>>>>>>>>>>>>>>thats the line i want to catch, in assembly above.
> Where is this call made in assembly ???*
> if (error < 0)
> goto out_free_secdata;
> BUG_ON(!mnt->mnt_sb);
> mnt->mnt_sb->s_flags |= MS_BORN;
>
> * error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata);*
> if (error)
> goto out_sb;
> .
> .
> .
> .
> .
> *out_sb:*
> dput(mnt->mnt_root);
> deactivate_locked_super(mnt->mnt_sb);
> *out_free_secdata*:
> free_secdata(secdata);
> *out_mnt:*
> free_vfsmnt(mnt);
> *out:* >>>368
> return ERR_PTR(error);
> }
You won't find a "direct *call* instruction, with function name, written in
english" because 'get_sb' is not a function[*] but a function pointer. And
moreover it is a member of a structure.
You will have to find out where a pointer to this structure is stored and
where a member relative to this structure it is referenced in a call
instruction. (Hint: It is the only function pointer inside 'type' which is
used in this function. Moreover, it is the only function pointer used in
this function at all.)
Regards,
Tobi
[*] To my shame, I have no clue about the subtleties of definitions of
entities in the C language. Please forgive me if my words don't accord
with these definitions.
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