svn commit: r340682 - stable/12/sys/amd64/include

[Mateusz Guzik]

Author: mjg
Date: Tue Nov 20 17:01:55 2018
New Revision: 340682
URL: https://svnweb.freebsd.org/changeset/base/340682

Log:
  MFC r339449:
  
      amd64: relax constraints in curthread and curpcb
  
      This makes the compiler less likely to reload the content from %gs.
  
      The 'P' modifier drops all synteax prefixes and 'n' constraint treats
      input as a known at compilation time immediate integer.
  
      Example reloading victim was spinlock_enter.

Modified:
  stable/12/sys/amd64/include/pcpu.h
Directory Properties:
  stable/12/   (props changed)

Modified: stable/12/sys/amd64/include/pcpu.h
==============================================================================
--- stable/12/sys/amd64/include/pcpu.h	Tue Nov 20 16:54:42 2018	(r340681)
+++ stable/12/sys/amd64/include/pcpu.h	Tue Nov 20 17:01:55 2018	(r340682)
@@ -227,8 +227,7 @@ __curthread(void)
 {
 	struct thread *td;
 
-	__asm("movq %%gs:%1,%0" : "=r" (td)
-	    : "m" (*(char *)OFFSETOF_CURTHREAD));
+	__asm("movq %%gs:%P1,%0" : "=r" (td) : "n" (OFFSETOF_CURTHREAD));
 	return (td);
 }
 #ifdef __clang__
@@ -242,7 +241,7 @@ __curpcb(void)
 {
 	struct pcb *pcb;
 
-	__asm("movq %%gs:%1,%0" : "=r" (pcb) : "m" (*(char *)OFFSETOF_CURPCB));
+	__asm("movq %%gs:%P1,%0" : "=r" (pcb) : "n" (OFFSETOF_CURPCB));
 	return (pcb);
 }
 #define	curpcb		(__curpcb())