svn commit: r356835 - head/sys/riscv/riscv

[Mitchell Horne]

Author: mhorne
Date: Fri Jan 17 17:03:25 2020
New Revision: 356835
URL: https://svnweb.freebsd.org/changeset/base/356835

Log:
  RISC-V: fix global pointer assignment at boot
  
  As part of the RISC-V ABI, the gp register is expected to initialized
  with the address of __global_pointer$ as early as possible. This allows
  loads and stores from .sdata to be relaxed based on the value of gp. In
  locore.S we do this initialization twice, once each for va and mpva.
  However, in both cases the initialization is preceded by an la
  instruction, which in theory could be relaxed by the linker.
  
  Move the initialization of gp to be slightly earlier (before la
  cpu_exception_handler), and add an additional gp initialization at the
  very beginning of _start, before virtual memory is set up.
  
  Reported by:	jrtc27
  Reviewed by:	jrtc27
  Differential Revision:	https://reviews.freebsd.org/D23139

Modified:
  head/sys/riscv/riscv/locore.S

Modified: head/sys/riscv/riscv/locore.S
==============================================================================
--- head/sys/riscv/riscv/locore.S	Fri Jan 17 16:48:20 2020	(r356834)
+++ head/sys/riscv/riscv/locore.S	Fri Jan 17 17:03:25 2020	(r356835)
@@ -53,6 +53,12 @@
 	.text
 	.globl _start
 _start:
+	/* Set the global pointer */
+.option push
+.option norelax
+	lla	gp, __global_pointer$
+.option pop
+
 	/* Get the physical address kernel loaded to */
 	lla	t0, virt_map
 	ld	t1, 0(t0)
@@ -168,6 +174,11 @@ _start:
 
 	.align 2
 va:
+	/* Set the global pointer again, this time with the virtual address. */
+.option push
+.option norelax
+	lla	gp, __global_pointer$
+.option pop
 
 	/* Setup supervisor trap vector */
 	la	t0, cpu_exception_handler
@@ -177,12 +188,6 @@ va:
 	li	t0, 0
 	csrw	sscratch, t0
 
-	/* Set the global pointer */
-.option push
-.option norelax
-	la	gp, __global_pointer$
-.option pop
-
 	/* Initialize stack pointer */
 	la	s3, initstack_end
 	mv	sp, s3
@@ -322,6 +327,12 @@ ENTRY(mpentry)
 
 	.align 2
 mpva:
+	/* Set the global pointer again, this time with the virtual address. */
+.option push
+.option norelax
+	lla	gp, __global_pointer$
+.option pop
+
 	/* Setup supervisor trap vector */
 	la	t0, cpu_exception_handler
 	csrw	stvec, t0
@@ -329,12 +340,6 @@ mpva:
 	/* Ensure sscratch is zero */
 	li	t0, 0
 	csrw	sscratch, t0
-
-	/* Set the global pointer */
-.option push
-.option norelax
-	la	gp, __global_pointer$
-.option pop
 
 	call	init_secondary
 END(mpentry)