Re: [PATCH v1 6/7] DCE/DSE: riscv: add HAVE_TRIM_UNUSED_SYSCALLS support

[Zhangjin Wu <falcon@tinylab.org>]

Hi, Arnd

> On Tue, Sep 26, 2023, at 00:42, Zhangjin Wu wrote:
> > For HAVE_TRIM_UNUSED_SYSCALLS, the syscall tables are hacked with the
> > inputing unused_syscalls.
> >
> > Firstly, the intermediate preprocessed .i files are generated from the
> > original C version of syscall tables respectively, and named with a
> > 'used' suffix: syscall_table_used.i, compat_syscall_table_used.i.
> >
> > Secondly, all of the unused syscalls are commented.
> >
> > At last, two new objective files sufixed with 'used' are generated from
> > the hacked .i files and they are linked into the eventual kernel image.
> >
> > Signed-off-by: Zhangjin Wu <falcon@tinylab.org>
> 
> As mentioned in my comment on the mips patch, hacking the preprocessed
> file here is too much strain on the old infrastructure, the
> asm-generic/unistd.h file is already too hard to understand for
> anyone and in need of an overhaul, so let's work together on fixing
> it up first.
>

Ok, I was thinking about using asm/syscall_table.h instead of asm/unistd.h like mips.

    void * const sys_call_table[NR_syscalls] = {
    	[0 ... NR_syscalls - 1] = __riscv_sys_ni_syscall,
    #include <asm/syscall_table.h>
    };

Therefore, we can generate syscall_table.h from asm/unist.h with a tool like scripts/syscallused.sh

Another solution may be firstly generate a list of `#define __USED_NR_##call 1`
for the used syscalls from Kconfig symbol, and then change __SYSCALL() macro
to:

   #define __SYSCALL(nr, call)     [nr] = __is_defined(__USED_NR_##call) ? __riscv_##call : __riscv_sys_ni_syscall,

`include/linux/kconfig.h` defined the '__is_defined'.

This method may work for the archs with .tbl files too.

Thanks,
Zhangjin

>       Arnd