From 2f663f61def07fbe500fdbeb60ecf89204e58a8c Mon Sep 17 00:00:00 2001
From: Berkus Decker <berkus+github@metta.systems>
Date: Wed, 14 Oct 2020 03:19:01 +0300
Subject: [PATCH] Move stack start constant to linker script

---
 linker/aarch64.ld                |  1 +
 nucleus/src/arch/aarch64/boot.rs | 25 +++++++++++++++++++------
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/linker/aarch64.ld b/linker/aarch64.ld
index d70349e..62c81cc 100644
--- a/linker/aarch64.ld
+++ b/linker/aarch64.ld
@@ -13,6 +13,7 @@ ENTRY(_boot_cores);
 SECTIONS
 {
     . = 0x80000; /* AArch64 boot address is 0x80000, 4K-aligned */
+    __STACK_START = .; /* Stack grows from here on down. */
     __BOOT_START = .;
     .text :
     {
diff --git a/nucleus/src/arch/aarch64/boot.rs b/nucleus/src/arch/aarch64/boot.rs
index 95b96e1..f89a887 100644
--- a/nucleus/src/arch/aarch64/boot.rs
+++ b/nucleus/src/arch/aarch64/boot.rs
@@ -45,11 +45,12 @@ unsafe fn reset() -> ! {
         // Boundaries of the .bss section, provided by the linker script
         static mut __BSS_START: u64;
         static mut __BSS_END: u64;
+        // Stack placed before first executable instruction
+        static __STACK_START: u64;
     }
 
     // Set stack pointer. Used in case we started in EL1.
-    const STACK_START: u64 = 0x80_000;
-    SP.set(STACK_START);
+    SP.set(&__STACK_START as *const u64 as u64);
 
     // Zeroes the .bss section
     r0::zero_bss(&mut __BSS_START, &mut __BSS_END);
@@ -94,8 +95,14 @@ fn setup_and_enter_el1_from_el2() -> ! {
 
     // Set up SP_EL1 (stack pointer), which will be used by EL1 once
     // we "return" to it.
-    const STACK_START: u64 = 0x80_000;
-    SP_EL1.set(STACK_START);
+    extern "C" {
+        // Stack placed before first executable instruction
+        static __STACK_START: u64;
+    }
+    // SAFETY: Only single core is booting and accessing this constant.
+    unsafe {
+        SP_EL1.set(&__STACK_START as *const u64 as u64);
+    }
 
     // Use `eret` to "return" to EL1. This will result in execution of
     // `reset()` in EL1.
@@ -159,8 +166,14 @@ fn setup_and_enter_el1_from_el3() -> ! {
 
     // Set up SP_EL1 (stack pointer), which will be used by EL1 once
     // we "return" to it.
-    const STACK_START: u64 = 0x80_000;
-    SP_EL1.set(STACK_START);
+    extern "C" {
+        // Stack placed before first executable instruction
+        static __STACK_START: u64;
+    }
+    // SAFETY: Only single core is booting and accessing this constant.
+    unsafe {
+        SP_EL1.set(&__STACK_START as *const u64 as u64);
+    }
 
     // Use `eret` to "return" to EL1. This will result in execution of
     // `reset()` in EL1.