On Thu, Apr 22, 2021 at 05:56:32PM -0500, Segher Boessenkool wrote:
> On Fri, Apr 09, 2021 at 05:09:07PM -0400, Michael Meissner wrote:
> > Fix logic error in 32-bit trampolines, PR target/98952.
> > 
> > The test in the PowerPC 32-bit trampoline support is backwards.  It aborts
> > if the trampoline size is greater than the expected size.  It should abort
> > when the trampoline size is less than the expected size.
> 
> > 	PR target/98952
> > 	* config/rs6000/tramp.S (__trampoline_setup): Fix trampoline size
> > 	comparison in 32-bit.
> 
> > --- a/libgcc/config/rs6000/tramp.S
> > +++ b/libgcc/config/rs6000/tramp.S
> > @@ -64,8 +64,7 @@ FUNC_START(__trampoline_setup)
> >          mflr	r11
> >          addi	r7,r11,trampoline_initial-4-.LCF0 /* trampoline address -4 */
> >  
> > -	li	r8,trampoline_size	/* verify that the trampoline is big enough */
> > -	cmpw	cr1,r8,r4
> > +	cmpwi	cr1,r4,trampoline_size	/* verify that the trampoline is big enough */
> >  	srwi	r4,r4,2		/* # words to move */
> >  	addi	r9,r3,-4	/* adjust pointer for lwzu */
> >  	mtctr	r4
> 
> As Will says, it looks like the ELFv2 version has the same bug.  Please
> fix that the same way.

Yes it has the same bug.  However in practice it would never be hit, since this
bug is 32-bit, and we only build 64-bit systems with ELF v2.  I did fix it.

> In the commit message and the changelog, point out that you folded the
> cmp with the li while you were at it.  It is easier to read code like
> this so the change is fine, but do point it out.
> 
> Can you test this in a testcase somehow?  That would have found the
> ELFv2 case, for example.

I created a test case calling __trampoline_setup with a larger buffer.  If it
doesn't abort the test passes.

> Okay for trunk.  Okay for backport to 11 when that branch opens again.
> Does this need more backports?  (Those should follow after 11 of
> course).

Bill mentioned we may want to backport this to earlier branches before they are
frozen.  Tulio, are backports to earlier revisions important?

I will attach the patch that I just commited.

-- 
Michael Meissner, IBM
IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA
email: meissner@linux.ibm.com, phone: +1 (978) 899-4797