Kernel: Move Prekernel assembly utils to aarch64/ASM_wrapper.h

By moving these functions to the ASM_wrapper.h file, we can get rid of
another Prekernel file.

Kernel/Arch/aarch64/ASM_wrapper.h

@@ -1,5 +1,8 @@
 /*
  * Copyright (c) 2021, James Mintram <me@jamesrm.com>
+ * Copyright (c) 2021, Nico Weber <thakis@chromium.org>
+ * Copyright (c) 2021, Marcin Undak <mcinek@gmail.com>
+ * Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -51,4 +54,38 @@ inline ExceptionLevel get_current_exception_level()
     return static_cast<ExceptionLevel>(current_exception_level);
 }
 
+inline void wait_cycles(int n)
+{
+    // This is probably too fast when caching and branch prediction is turned on.
+    // FIXME: Make timer-based.
+    asm("mov x0, %[value]\n"
+        "0:\n"
+        "    subs x0, x0, #1\n"
+        "    bne 0b" ::[value] "r"(n)
+        : "x0");
+}
+
+inline void el1_vector_table_install(void* vector_table)
+{
+    asm("msr VBAR_EL1, %[value]" ::[value] "r"(vector_table));
+}
+
+inline void enter_el2_from_el3()
+{
+    asm volatile("    adr x0, entered_el2\n"
+                 "    msr elr_el3, x0\n"
+                 "    eret\n"
+                 "entered_el2:" ::
+                     : "x0");
+}
+
+inline void enter_el1_from_el2()
+{
+    asm volatile("    adr x0, entered_el1\n"
+                 "    msr elr_el2, x0\n"
+                 "    eret\n"
+                 "entered_el1:" ::
+                     : "x0");
+}
+
 }

Kernel/Arch/aarch64/Prekernel/Aarch64_asm_utils.S

@@ -1,48 +0,0 @@
-/*
- * Copyright (c) 2021, Nico Weber <thakis@chromium.org>
- * Copyright (c) 2021, Marcin Undak <mcinek@gmail.com>
- * Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com>
- *
- * SPDX-License-Identifier: BSD-2-Clause
- */
-
-.global wait_cycles
-.type wait_cycles, @function
-wait_cycles:
-Lstart:
-  // This is probably too fast when caching and branch prediction is turned on.
-  // FIXME: Make timer-based.
-  subs x0, x0, #1
-  bne Lstart
-  ret
-
-.global enter_el2_from_el3
-.type enter_el2_from_el3, @function
-enter_el2_from_el3:
-  adr x0, entered_el2
-  msr elr_el3, x0
-  eret
-entered_el2:
-  ret
-
-.global enter_el1_from_el2
-.type enter_el1_from_el2, @function
-enter_el1_from_el2:
-  adr x0, entered_el1
-  msr elr_el2, x0
-  eret
-entered_el1:
-  ret
-
-//
-// Installs the EL1 vector table
-// Args:
-//      x0 - Address of vector table
-//
-// This function doesn't return a value
-//
-.global el1_vector_table_install
-.type el1_vector_table_install, @function
-el1_vector_table_install:
-    msr VBAR_EL1, x0
-    ret

Kernel/Arch/aarch64/Prekernel/Aarch64_asm_utils.h

@@ -1,14 +0,0 @@
-/*
- * Copyright (c) 2021, Marcin Undak <mcinek@gmail.com>
- *
- * SPDX-License-Identifier: BSD-2-Clause
- */
-
-#pragma once
-
-extern "C" void wait_cycles(int n);
-extern "C" void el1_vector_table_install(void* vector_table);
-
-// CPU initialization functions
-extern "C" [[noreturn]] void return_from_el2();
-extern "C" [[noreturn]] void return_from_el3();

Kernel/Arch/aarch64/Prekernel/PrekernelExceptions.cpp

@@ -5,14 +5,10 @@
  */
 
 #include <Kernel/Arch/aarch64/ASM_wrapper.h>
-#include <Kernel/Arch/aarch64/Prekernel/Aarch64_asm_utils.h>
 #include <Kernel/Arch/aarch64/Prekernel/Prekernel.h>
 #include <Kernel/Arch/aarch64/Registers.h>
 #include <Kernel/Panic.h>
 
-extern "C" void enter_el2_from_el3();
-extern "C" void enter_el1_from_el2();
-
 using namespace Kernel;
 
 namespace Prekernel {
@@ -43,8 +39,9 @@ static void drop_to_el2()
     Aarch64::SPSR_EL3::write(saved_program_status_register_el3);
 
     // This will jump into os_start() below
-    enter_el2_from_el3();
+    Aarch64::Asm::enter_el2_from_el3();
 }
+
 static void drop_to_el1()
 {
     Aarch64::HCR_EL2 hypervisor_configuration_register_el2 = {};
@@ -62,7 +59,7 @@ static void drop_to_el1()
     saved_program_status_register_el2.M = Aarch64::SPSR_EL2::Mode::EL1t;
 
     Aarch64::SPSR_EL2::write(saved_program_status_register_el2);
-    enter_el1_from_el2();
+    Aarch64::Asm::enter_el1_from_el2();
 }
 
 static void set_up_el1()

Kernel/Arch/aarch64/Processor.cpp

@@ -8,7 +8,6 @@
 
 #include <Kernel/Arch/Processor.h>
 #include <Kernel/Arch/aarch64/ASM_wrapper.h>
-#include <Kernel/Arch/aarch64/Prekernel/Aarch64_asm_utils.h>
 #include <Kernel/Arch/aarch64/Prekernel/Prekernel.h>
 
 extern "C" uintptr_t vector_table_el1;
@@ -28,7 +27,7 @@ void Processor::initialize(u32 cpu)
     Prekernel::drop_to_exception_level_1();
 
     // Load EL1 vector table
-    el1_vector_table_install(&vector_table_el1);
+    Kernel::Aarch64::Asm::el1_vector_table_install(&vector_table_el1);
 
     g_current_processor = this;
 }

Kernel/Arch/aarch64/RPi/GPIO.cpp

@@ -4,11 +4,10 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <Kernel/Arch/aarch64/ASM_wrapper.h>
 #include <Kernel/Arch/aarch64/RPi/GPIO.h>
 #include <Kernel/Arch/aarch64/RPi/MMIO.h>
 
-extern "C" void wait_cycles(int n);
-
 namespace Prekernel {
 
 // See BCM2835-ARM-Peripherals.pdf section "6 General Purpose I/O" or bcm2711-peripherals.pdf "Chapter 5. General Purpose I/O".
@@ -73,7 +72,7 @@ void GPIO::internal_enable_pins(u32 enable[2], PullUpDownState state)
     m_registers->pull_up_down_enable = static_cast<u32>(state);
 
     // 2. Wait 150 cycles – this provides the required set-up time for the control signal
-    wait_cycles(150);
+    Kernel::Aarch64::Asm::wait_cycles(150);
 
     // 3. Write to GPPUDCLK0/1 to clock the control signal into the GPIO pads you wish to
     //    modify – NOTE only the pads which receive a clock will be modified, all others will
@@ -82,7 +81,7 @@ void GPIO::internal_enable_pins(u32 enable[2], PullUpDownState state)
     m_registers->pull_up_down_enable_clock.bits[1] = enable[1];
 
     // 4. Wait 150 cycles – this provides the required hold time for the control signal
-    wait_cycles(150);
+    Kernel::Aarch64::Asm::wait_cycles(150);
 
     // 5. Write to GPPUD to remove the control signal
     m_registers->pull_up_down_enable = 0;

Kernel/Arch/aarch64/init.cpp

@@ -23,8 +23,6 @@
 static void draw_logo();
 static u32 query_firmware_version();
 
-extern "C" void wait_cycles(int n);
-
 struct TrapFrame {
     u64 x[31];     // Saved general purpose registers
     u64 spsr_el1;  // Save Processor Status Register, EL1

Kernel/CMakeLists.txt

@@ -398,7 +398,6 @@ if (NOT "${SERENITY_ARCH}" STREQUAL "aarch64")
     )
 else()
     set(PREKERNEL_SOURCES
-        Arch/aarch64/Prekernel/Aarch64_asm_utils.S
         Arch/aarch64/Prekernel/boot.S
         Arch/aarch64/Prekernel/PrekernelExceptions.cpp
         Arch/aarch64/Prekernel/PrekernelMMU.cpp