Re: [RFC][PATCH 4/4] x86_32: Provide consistent pt_regs

[Ingo Molnar]

* Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:

> On Wed, May 08, 2019 at 09:49:05AM +0200, Peter Zijlstra wrote:
> > Currently pt_regs on x86_32 has an oddity in that kernel regs
> > (!user_mode(regs)) are short two entries (esp/ss). This means that any
> > code trying to use them (typically: regs->sp) needs to jump through
> > some unfortunate hoops.
> > 
> > Change the entry code to fix this up and create a full pt_regs frame.
> > 
> > This then simplifies:
> > 
> >   - ftrace
> >   - kprobes
> >   - stack unwinder
> >   - ptrace
> >   - kdump
> >   - kgdb
> > 
> > Hated-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > ---
> >  arch/x86/entry/entry_32.S         |  105 ++++++++++++++++++++++++++++++++++----
> >  arch/x86/include/asm/kexec.h      |   17 ------
> >  arch/x86/include/asm/ptrace.h     |   17 ------
> >  arch/x86/include/asm/stacktrace.h |    2 
> >  arch/x86/kernel/crash.c           |    8 --
> >  arch/x86/kernel/ftrace_32.S       |   81 ++++++++++++++++-------------
> >  arch/x86/kernel/kgdb.c            |    8 --
> >  arch/x86/kernel/kprobes/common.h  |    4 -
> >  arch/x86/kernel/kprobes/core.c    |   29 ++++------
> >  arch/x86/kernel/kprobes/opt.c     |   20 ++++---
> >  arch/x86/kernel/process_32.c      |   16 +----
> >  arch/x86/kernel/ptrace.c          |   29 ----------
> >  arch/x86/kernel/time.c            |    3 -
> >  arch/x86/kernel/unwind_frame.c    |   32 +----------
> >  arch/x86/kernel/unwind_orc.c      |    2 
> >  15 files changed, 181 insertions(+), 192 deletions(-)
> 
> Very nice diffstat.  This moves all the pain to the 32-bit entry code
> where it belongs.

Yes, that's very convincing and looks like a nice simplification of 
32-bit x86 entry concepts overall.

Assuming it's correct, the question is whether Linus still hates it? :-)

Thanks,

	Ingo