Re: Possible regression by ab037dd87a2f (powerpc/vdso: Switch VDSO to generic C implementation.)

On Tue, 2021-07-27 at 10:45 +0200, Paul Menzel wrote:

Dear Christophe,


On ppc64le Go 1.16.2 from Ubuntu 21.04 terminates with a segmentation 
fault [1], and it might be related to *[release-branch.go1.16] runtime: 
fix crash during VDSO calls on PowerPC* [2], conjecturing that commit 
ab037dd87a2f (powerpc/vdso: Switch VDSO to generic C implementation.) 
added in Linux 5.11 causes this.

If this is indeed the case, this would be a regression in userspace. Is 
there a generic fix or should the change be reverted?

From the look at the links you posted, this appears to be completely
broken assumptions by Go that some registers don't change while calling
what essentially are external library functions *while inside those
functions* (ie in this case from a signal handler).

I suppose it would be possible to build the VDSO with gcc arguments to
make it not use r30, but that's just gross...

Cheers,
Ben.