git: d866f1d4f968 - stable/14 - aarch64: Save correct value of x18 on trapframe for nested faults

The branch stable/14 has been updated by jhb:

URL: https://cgit.FreeBSD.org/src/commit/?id=d866f1d4f968f8ead4765944d82f4af640815678

commit d866f1d4f968f8ead4765944d82f4af640815678
Author:     Konrad Witaszczyk <def@FreeBSD.org>
AuthorDate: 2025-09-16 11:21:57 +0000
Commit:     John Baldwin <jhb@FreeBSD.org>
CommitDate: 2025-12-18 18:25:14 +0000

    aarch64: Save correct value of x18 on trapframe for nested faults
    
    x18 is overwritten with a temporary copy of the kernel stack pointer
    when it is saved in the trapframe.  This does not matter in terms of
    function since nested exception return does not restore x18 from the
    trapframe, but it does mean that examining x18 in a debugger in stack
    frames above a nested fault outputs the wrong register value.
    
    To fix, compute the value of the original stack pointer to save in x18
    later after the trapframe has been constructed.
    
    Reviewed by:    jhb, andrew
    Sponsored by:   AFRL, DARPA
    Differential Revision:  https://reviews.freebsd.org/D52472
    
    (cherry picked from commit 99213b3c352cdf568ea7cf5b4dddb1879f16a601)
---
 sys/arm64/arm64/exception.S | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/sys/arm64/arm64/exception.S b/sys/arm64/arm64/exception.S
index 0457efe77ba8..07223fcb069d 100644
--- a/sys/arm64/arm64/exception.S
+++ b/sys/arm64/arm64/exception.S
@@ -38,7 +38,6 @@
  */
 .macro	save_registers_head el
 .if \el == 1
-	mov	x18, sp
 	stp	x0,  x1,  [sp, #-(TF_SIZE - TF_X + 128)]!
 .else
 	stp	x0,  x1,  [sp, #-(TF_SIZE - TF_X)]!
@@ -57,7 +56,9 @@
 	stp	x24, x25, [sp, #(24 * 8)]
 	stp	x26, x27, [sp, #(26 * 8)]
 	stp	x28, x29, [sp, #(28 * 8)]
-.if \el == 0
+.if \el == 1
+	add	x18, sp, #(TF_SIZE - TF_X + 128)
+.else
 	mrs	x18, sp_el0
 .endif
 	mrs	x10, elr_el1