Changeset 14b5c30f in mainline

Timestamp:

2020-02-07T11:22:28Z (5 years ago)

Author:

Martin Decky <martin@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

db17889

Parents:

51da086

Message:

arm64: reset the kernel SP to its base value before entering user space

Without doing this, the part of the kernel stack that has been in use
before entering user space will remain forever unaccessible and wasted.

This is analogous to what is being done (by various means) on other
platforms.

File:

• kernel/arch/arm64/src/arm64.c (modified) (2 diffs)

kernel/arch/arm64/src/arm64.c

@@ -167 +167 @@
         asm volatile (
             /*
-             * Clear all general-purpose registers, except x0 that holds an
-             * argument for the user space.
+             * Reset the kernel stack to its base value.
+             *
+             * Clear all general-purpose registers,
+             * except x0 that holds an argument for
+             * the user space.
              */
+            "mov sp, %[kstack]\n"
             "mov x0, %[uspace_uarg]\n"
             "mov x1, #0\n"
@@ -202 +206 @@
             "mov x30, #0\n"
             "eret\n"
-            :: [uspace_uarg] "r" (kernel_uarg->uspace_uarg)
+            :: [uspace_uarg] "r" (kernel_uarg->uspace_uarg),
+               [kstack] "r" (((uint64_t) (THREAD->kstack))
+                   + MEM_STACK_SIZE - SP_DELTA)
         );