Re: [PATCH 00/13] jump label v9

From: Mathieu Desnoyers
Date: Tue Jun 15 2010 - 11:44:49 EST

* Jason Baron (jbaron@xxxxxxxxxx) wrote:
> On Mon, Jun 14, 2010 at 08:47:59PM -0700, David Miller wrote:
> > Jason, I'm really at wits end about this patch set. To say
> > that trying to test our your patches is frustrating for me
> > so far would be an understatement.
> >
> > Nothing you ever post builds for me, not one patch set has
> > built properly.
> >
> > I can also tell that you're just blindly making changes to the
> > sparc bits and not trying to build test them at all:
> >
> > 1) Even though you created the jump_label_t, and made it properly
> > a u32 on sparc, you left the assembler using ".xword" to
> > record the entries.
> >
> > 2) The sparc "struct jump_label" still calls it's third member "name",
> > it needs to be "key" or else the build breaks.
> >
> > 3) Eventhough the sparc JUMP_LABEL macro was fixed to have two args,
> > the first arg was left as "tag" instead of being renamed to "key"
> > and that name change propaged into the asm in the macro expansion.
> >
> > I took care of that locally to try and test this, but then I hit the
> > current major problem which is that you're using things like
> > text_poke_early() unconditionally, but that is an X86-only facility
> > implemented by x86's alternative mechanism.
> >
> > Also, kernel/jump_label.c only gets the ERR_PTR() definitions
> > indirectly on the x86 platform, it needs to include linux/err.h
> > directly to make sure those things are available on every platform.
> >
> > You gave me the impression a few iterations ago that you were doing
> > build testing on sparc64 using cross-compilers, or that you would
> > start to do so. You're obviously not, could you please start doing so
> > and let me know when you've at least build tested your jump-label
> > patch series on sparc64 and at least one architecture that lacks
> > jump-label support?
> >
> > Thanks.
> Hi David,
> Yes, I've tried to help re-write the sparc bits to the current api.
> However, I did not test the sparc enabled jump-label bits, b/c I need an
> updated cross compiler to do so (that has jump label support). However, I
> certainly did build test the patches on powerpc, which lacks jump-label support,
> so I know it builds on at least one architecture that lacks jump-label support
> as you've mentioned. And I did this specifically, since you requested this
> testing.
> I guess I was hoping we could work more collaboratively on the sparc
> bits. A couple lines of code have fixed the issues that you've brought up.
> Sorry, if i mislead you. I really just want to do what is best for the linux
> kernel, if that's going off and figuring out how to compile a new sparc
> enabled jump label compiler for sparc, I will do it.

Hi Jason,

It makes me wonder if anyone had success building a gcc 4.5
Intel-to-sparc64 cross-compiler ? Usually, the crosstool-like suites are
a few versions behind. I'm aware that this is not trivial, as
cross-compilers have a tendency to refuse to get built in certain
occasions (such as being a recent less tested version). I'd recommend
you focus on this as a first step before resubmitting.

> And I do agree,
> that leaving text_poke_early() is my mistake. However, maybe we can
> discuss this issue? For example, the reason I have it in the code is b/c
> x86 determines the best no-op at run-time. Are other architectures going
> to have to require this kind of functionality. Or like sparc, are we
> going to be able to generally hard-code the nops on non-x86 at
> compile-time?

You might want to create "dumb" text_poke() and text_poke_early()
implementations on other architectures that wraps kernel text updates
pretty simply. The implementation is trivial if the architecture does
not write-protect the text pages, but becomes more evolved when it does.



> thanks. And again I apologize for any wasted cycles that I've caused.
> -Jason

Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
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