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SubjectRe: PATCH: Add --size-check=[error|warning]

(resend, fixed the To line)

* Alan Modra <amodra@gmail.com> wrote:

> On Mon, Mar 14, 2011 at 10:55:34AM +0100, Ingo Molnar wrote:
> > The thing is, it is absolutely, breath-takingy incompetent for
>
> kernel developers to write such poor asm! And not notice the error
> for 4 years! [...]

It is not 'poor asm'.

The 'bug' is just a slight assymetry in ENTRY()/END() debug-symbols sequences, with
lots of assembly code between the ENTRY() and the END(). Here's an example:

ENTRY(xen_do_hypervisor_callback) # do_hypervisor_callback(struct *pt_regs)
...
END(do_hypervisor_callback)

Human reviewers almost never catch such small mismatches, and binutils never even
warned about it either - for over a decade.

Now kernel bisections are insta-broken on latest binutils, and there's nothing to do
about it on the kernel side as during bisection all later fixes are unfolded. The
fix itself i already applied - but my argument was not about that:

> [...] Oh, and the binutils developers to write such a poor assembler in the first
> place. ;-)
>
> Seriously, you are complaining because something is fixed??

No, i reported this bug because the kernel build gets broken going back 130,000
commits, breaking bisection and causing other damage - while issuing a warning
message would achieve the same effect of warning the developer about the mismatch.

> > The correct solution is to turn it into a warning as me and others have suggested.
>
> I disagree. The whole world is not the linux kernel. I think HJ is
> bending over backwards to even offer a switch that turns the error
> into a warning.

It's not about a switch at all - it's to not break builds by default. I.e. the
default behavior should be to issue a warning and ignore the directive.

This is a very simple concept of compatibility: the build environment should always
be very permissive - stuff that build fine before should be allowed to build.

Also, i hope you are not suggesting to break projects just because they are not
important to you personally? The fix is exceedingly simple to do for the binutils
project - and impossible to do for the kernel project (because during bisection -
which is a very powerful debugging tool - older versions of the source get checked
out).

Thanks,

Ingo


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