On October 13, 2025 7:06:55 AM PDT, Dave Hansen [off-list ref] wrote:

On 10/13/25 02:20, Thomas Weißschuh wrote:

quoted

-int __vdso_getcpu(unsigned int *cpu, unsigned int *node, struct getcpu_cache *unused);
-int __vdso_getcpu(unsigned int *cpu, unsigned int *node, struct getcpu_cache *unused)
+int __vdso_getcpu(unsigned int *cpu, unsigned int *node, void *unused);
+int __vdso_getcpu(unsigned int *cpu, unsigned int *node, void *unused)
 {
 	int cpu_id;

It would ideally be nice to have a _bit_ more history on this about
how it became unused any why there is such high confidence that
userspace never tries to use it.

Let's say someone comes along in a few years and wants to use this
'unused' parameter. Could they?

I believe it was a private storage area for the kernel to use... which it doesn't. Not doing anything at all with the pointer is perfectly legitimate.