Reuse gp register for pcpu pointer.

gp (global pointer) is used by compiler in userland only,
so re-use it for pcpup in kernel, save it on stack on switching
out to userland and load back on return to kernel.

Discussed with:	jhb, andrew, kib
Sponsored by:	DARPA, AFRL
Sponsored by:	HEIF5
Differential Revision:	https://reviews.freebsd.org/D5178

1 files changed, 5 insertions, 2 deletions

diff --git a/sys/riscv/include/pcpu.h b/sys/riscv/include/pcpu.h
index c60a95428fe1..7dfe23d991bf 100644
--- a/sys/riscv/include/pcpu.h
+++ b/sys/riscv/include/pcpu.h
@@ -47,8 +47,11 @@ extern struct pcpu *pcpup;
 static inline struct pcpu *
 get_pcpu(void)
 {
+	struct pcpu *pcpu;
 
-	return (pcpup);
+	__asm __volatile("mv %0, gp" : "=&r"(pcpu));
+
+	return (pcpu);
 }
 
 static inline struct thread *
@@ -56,7 +59,7 @@ get_curthread(void)
 {
 	struct thread *td;
 
-	td = (struct thread *)*(uint64_t *)pcpup;
+	__asm __volatile("ld %0, 0(gp)" : "=&r"(td));
 
 	return (td);
 }