Re: [PATCH] tile: support GENERIC_KERNEL_THREAD and GENERIC_KERNEL_EXECVE

[Catalin Marinas <catalin.marinas@arm.com>]

Hi Al,

Sorry, couldn't reply earlier.

On Sat, Oct 20, 2012 at 04:34:01PM +0100, Al Viro wrote:
> On Sat, Oct 20, 2012 at 09:06:57AM -0400, Chris Metcalf wrote:
> > First, the compat_sys_execve() declaration provided in
> > arch/tile/include/asm/compat.h isn't right, so I deleted that (you had only
> > deleted the PTREGS_SYSCALL trampoline declaration, _compat_sys_execve).
> > 
> > However, then arch/tile/kernel/compat.c failed to build, because
> > <linux/compat.h> is included before <asm/unistd.h>, and <asm/unistd.h>
> > provides __ARCH_WANT_SYS_EXECVE, and so we end up with no declaration at
> > all for compat_sys_execve.  For most platforms this is no big deal, but on
> > tile we use the __SYSCALL #define to provide the actual syscall table, and
> > for that to work we need a declaration in scope for each syscall at the
> > time we create the table.
> > 
> > The best solution seems likely to be to copy the other place in
> > <linux/compat.h> where we need to do something configurable (that is,
> > CONFIG_ARCH_WANT_OLD_COMPAT_IPC), and just convert __ARCH_WANT_SYS_EXECVE
> > to be a Kconfig option.
> 
> Frankly, I hope to get rid of the damn thing completely.  By now we have
> at least some variant of execve conversions for just about everything;
> I certainly hope that by the beginning of the next cycle we'll have it
> defined on everything.  And put unconditional declarations in syscalls.h
> and compat.h
> 
> Actually, we can make the declaration in linux/compat.h unconditional
> right now.  The only obstacle is the situation on arm64; there the mainline
> has C variant of that sucker (with struct pt_regs * in arguments) in
> arch/arm64/kernel/sys_compat.c.  So we could ask Linus to pull
> git://git.kernel.org/pub/scm/linux/kernel/git/cmarinas/linux-aarch64 execve
> and then do the following in one patch:
> 	introduce current_pt_regs() on tile (from your commit)
> 	get rid of pt_regs * argument in tile compat_sys_execve(), making it
> use current_pt_regs(); kill its wrapper
> 	kill the declarations of compat_sys_execve()/_compat_sys_execve()
> in tile asm/compat.h
> 	make declaration in linux/compat.h unconditional
> Note that this does *not* depend on kernel_thread/kernel_execve patch -
> kernel_execve() is never going to hit compat_sys_execve(), since it's
> only called from kernel threads and those are not going to be 32bit.
> After that we can do kernel_thread/kernel_execve commit and
> sys_execve() conversion with nothing outside of arch/tile touched.
> 
> Comments?  If Catalin feels that arm64 series needs more testing, we could
> reorder it a bit - all we really need there is getting rid of pt_regs argument
> in compat_sys_execve() and just as on tile, that isn't tied into kernel_execve
> and kernel_thread issues.

I don't mind merging it earlier (if Linus is ok to take it after the
merging window). It works fine in my tests.

-- 
Catalin