lkl: add make_syscall_tbl.sh to create syscall definition

[thehajime]

This patch fixes two issues:

1. crash when unsupported system call is called via lkl_syscall()

2. build takes long time since it creates syscall_defs.h evertime with
   vmlinux

3. is fixed by filtering-out ignored syscalls from syscall_table and
   returns ENOSYS. ignored syscalls are defined as __IGNORE_xxx in
   arch/lkl/include/asm/unistd.h.

4. is fixed by creating syscall_defs.h by a shell script when a build
   runs for the first time or unistd.h is updated.

A test case is added to check whether 1) works fine or not.

In order to add unsupported syscalls, we need to add entries
'__IGNORE_xx' as black list entries in asm/unistd.h so that lkl_syscall
will not be only generated but also returns ENOSYS on lkl_syscall().

This patch makes arch/lkl be able to generate syscall_defs.h without
changing include/linux/syscall.h and the requirement of objcopy and
section comment of ELF binary (vmlinux).

Signed-off-by: Hajime Tazaki thehajime@gmail.com

[thehajime]

1. I took a blacklist-based approach (i.e., defining ___IGNORE_xxx value in unistd.h) instead of while-list one (i.e., make a hole by STE() macro) to define supported system calls because the latter is going to happen very frequently which makes a lot to do when you add new syscalls.

if we prefer the other way around, I could update the patch.

2. I don't think current contents of __IGNORE_xx macro is not perfect: at least lkl_syscall(__NR_sysctl) still crashes. We need to work more to complete the definition.

[tavip]

A similar approach was used before commit 5c865ec. This approach is slower because after the kernel is compiled you need to search and grep the whole kernel tree vs just generating the info during the build.

[thehajime]

A similar approach was used before commit 5c865ec. This approach is slower because after the kernel is compiled you need to search and grep the whole kernel tree vs just generating the info during the build.

I'm also aware of this speed issue.

This patch improve the previous way by generating header files only during make ARCH=lkl at top directory while the previous script always generates when you execute ``make` at tools/lkl directory. This has a big impact when building vmlinux frequently.

[tavip]

Can one of the admins verify this patch?

[lurch]

"counterpart" should be just one word.
(with the space, it's easy to mis-read it as "64 bit counter")

[lurch]

Was this supposed to be an underscore instead of a comma?

[thehajime]

this is intentional.

[thehajime]

I'm closing this PR since it looks like marginal fix of the usability improvement. Will reopen if someone is interested in.