baremetal aarch64: create C version of multicore.S as well

Attempted to do the same for arm, but it failed.

baremetal/arch/aarch64/multicore.c

@@ -0,0 +1,45 @@
+/* https://cirosantilli.com/linux-kernel-module-cheat#arm-multicore
+ *
+ * Beware: things will blow up if the stack for CPU0 grow too much and
+ * reaches that of CPU1. This is why it is so hard to do multithreading
+ * without an OS that manages paging.
+ */
+
+#include <lkmc.h>
+
+uint64_t spinlock = 0;
+
+__asm__(
+".text\n"
+".global lkmc_cpu_not_0\n"
+"lkmc_cpu_not_0:\n"
+/* Put all CPUs except CPU1 to sleep. */
+"    cmp x0, 1\n"
+"    bne .Lsleep_forever\n"
+/* Prepare the stack for CPU1. This is what we need
+ * this assembly function for. */
+"    ldr x0, =(stack_top - 0x1000)\n"
+"    mov sp, x0\n"
+"    bl main_cpu1\n"
+".Lsleep_forever:\n"
+"    wfe\n"
+"    b .Lsleep_forever\n"
+);
+
+static void main_cpu1(void) {
+    spinlock = 1;
+    lkmc_arm_aarch64_dmb(sy);
+    lkmc_arm_aarch64_sev();
+    while (1) {
+        lkmc_arm_aarch64_wfe();
+    }
+}
+
+int main(void) {
+#if !LKMC_GEM5
+    lkmc_aarch64_psci_cpu_on(1, (uint64_t)main_cpu1, 0);
+#endif
+    while (!spinlock) {
+        lkmc_arm_aarch64_wfe();
+    }
+}

baremetal/arch/aarch64/no_bootloader/exit.S

@@ -0,0 +1,8 @@
+/* Test _exit. */
+
+#include <lkmc.h>
+
+.global lkmc_start
+lkmc_start:
+    mov x0, 0
+    bl _exit

baremetal/arch/aarch64/no_bootloader/multicore_asm.S

@@ -1,11 +1,15 @@
-/* https://cirosantilli.com/linux-kernel-module-cheat#arm-multicore */
+/* https://cirosantilli.com/linux-kernel-module-cheat#arm-multicore
+ *
+ * This has to be in no_bootloader
+ */
 
 #include <lkmc.h>
 
-LKMC_PROLOGUE
+.global lkmc_start
+lkmc_start:
     /* Reset spinlock. */
     mov x0, 0
-    ldr x1, =spinlock
+    ldr x1, =.Lspinlock
     str x0, [x1]
 
     /* Read cpu id into x1.
@@ -14,11 +18,11 @@ LKMC_PROLOGUE
      */
     mrs x1, mpidr_el1
     ands x1, x1, 3
-    beq cpu0_only
+    beq .Lcpu0_only
 .Lcpu1_only:
     /* Only CPU 1 reaches this point and sets the spinlock. */
     mov x0, 1
-    ldr x1, =spinlock
+    ldr x1, =.Lspinlock
     str x0, [x1]
     /* Ensure that CPU 0 sees the write right now.
      * Optional, but could save some useless CPU 1 loops.
@@ -34,7 +38,7 @@ LKMC_PROLOGUE
      */
     wfe
     b .Lcpu1_sleep_forever
-cpu0_only:
+.Lcpu0_only:
     /* Only CPU 0 reaches this point. */
 
 #if !LKMC_GEM5
@@ -61,11 +65,14 @@ cpu0_only:
     hvc 0
 #endif
 
-spinlock_start:
-    ldr x0, spinlock
+.Lspinlock_start:
+    ldr x0, .Lspinlock
     /* Hint CPU 0 to enter low power mode. */
     wfe
-    cbz x0, spinlock_start
-LKMC_EPILOGUE
-spinlock:
+    cbz x0, .Lspinlock_start
+
+    mov x0, 0
+    bl _exit
+
+.Lspinlock:
     .skip 8

baremetal/arch/aarch64/no_bootloader/semihost_exit.S

@@ -1,15 +1,19 @@
-/* https://cirosantilli.com/linux-kernel-module-cheat#semihosting */
+/* https://cirosantilli.com/linux-kernel-module-cheat#semihosting
+ *
+ * Since our stack pointer is not setup, we justa allocate a memory
+ * region to contain the semihosting arguments, which must be in memory.
+ */
 
 .global lkmc_start
 lkmc_start:
     mov x1, 0x26
     movk x1, 2, lsl 16
-    ldr x2, =semihost_args
+    ldr x2, =.Lsemihost_args
     str x1, [x2, 0]
     mov x0, 0
     str x0, [x2, 8]
     mov x1, x2
     mov w0, 0x18
     hlt 0xf000
-semihost_args:
+.Lsemihost_args:
     .skip 16

baremetal/arch/aarch64/semihost_exit.S

@@ -1,3 +1,5 @@
+/* https://cirosantilli.com/linux-kernel-module-cheat#semihosting */
+
 .global main
 main:
     /* 0x20026 == ADP_Stopped_ApplicationExit */

baremetal/arch/aarch64/svc.c

@@ -71,7 +71,7 @@ int main(void) {
     printf("&after_svc %p\n", &&after_svc);
     assert(myvar == 0);
     /* Max 16-bits. */
-    lkmc_svc(0xABCD);
+    lkmc_arm_aarch64_svc(0xABCD);
 after_svc:
     assert(myvar == 1);
     return 0;

baremetal/arch/aarch64/timer.c

@@ -113,7 +113,7 @@ int main(void) {
         enable_irq();
     }
     while (1) {
-        lkmc_wfi();
+        lkmc_arm_aarch64_wfi();
     }
     return 0;
 }

baremetal/arch/arm/multicore.c

@@ -0,0 +1,37 @@
+/* https://cirosantilli.com/linux-kernel-module-cheat#arm-multicore */
+
+#include <lkmc.h>
+
+uint64_t spinlock = 0;
+
+__asm__(
+".syntax unified\n"
+".text\n"
+".global lkmc_cpu_not_0\n"
+"lkmc_cpu_not_0:\n"
+"    cmp r0, 1\n"
+"    bne .Lsleep_forever\n"
+"    ldr sp, =(stack_top - 0x1000)\n"
+"    bl main_cpu1\n"
+".Lsleep_forever:\n"
+"    wfe\n"
+"    b .Lsleep_forever\n"
+);
+
+static void main_cpu1(void) {
+    spinlock = 1;
+    lkmc_arm_aarch64_dmb(sy);
+    lkmc_arm_aarch64_sev();
+    while (1) {
+        lkmc_arm_aarch64_wfe();
+    }
+}
+
+int main(void) {
+#if !LKMC_GEM5
+    lkmc_arm_psci_cpu_on(1, (uint32_t)main_cpu1, 0);
+#endif
+    while (!spinlock) {
+        lkmc_arm_aarch64_wfe();
+    }
+}

baremetal/arch/arm/no_bootloader/multicore_asm.S

@@ -2,24 +2,25 @@
 
 #include <lkmc.h>
 
-LKMC_PROLOGUE
+.global lkmc_start
+lkmc_start:
     mov r0, 0
-    ldr r1, =spinlock
+    ldr r1, =.Lspinlock
     str r0, [r1]
     /* Get CPU ID. */
     mrc p15, 0, r1, c0, c0, 5
     ands r1, r1, 3
-    beq cpu0_only
+    beq .Lcpu0_only
 .Lcpu1_only:
     mov r0, 1
-    ldr r1, =spinlock
+    ldr r1, =.Lspinlock
     str r0, [r1]
     dmb sy
     sev
 .Lcpu1_sleep_forever:
     wfe
     b .Lcpu1_sleep_forever
-cpu0_only:
+.Lcpu0_only:
 #if !LKMC_GEM5
     /* PSCI CPU_ON. */
     ldr r0, =0x84000003
@@ -28,11 +29,12 @@ cpu0_only:
     mov r3, 0
     hvc 0
 #endif
-spinlock_start:
-    ldr r0, spinlock
+.Lspinlock_start:
+    ldr r0, .Lspinlock
     wfe
     cmp r0, 0
-    beq spinlock_start
-LKMC_EPILOGUE
-spinlock:
+    beq .Lspinlock_start
+    mov r0, 0
+    bl _exit
+.Lspinlock:
     .skip 4

baremetal/lib/aarch64.S

@@ -2,6 +2,11 @@
 
 .global lkmc_start
 lkmc_start:
+    /* Make all CPUs except CPU0 sleep by default. */
+    mrs x0, mpidr_el1
+    ands x0, x0, 3
+    bne lkmc_cpu_not_0
+
     /* Load the vector table. */
     ldr x0, =lkmc_vector_table
     msr vbar_el1, x0
@@ -41,3 +46,8 @@ LKMC_WEAK(lkmc_vector_trap_handler)
     bl abort
 lkmc_vector_trap_handler_error_message:
     .asciz "error: unexpected interrupt"
+
+/* Default action for CPUs besides the first one: sleep forever. */
+LKMC_WEAK(lkmc_cpu_not_0)
+    wfe
+    b lkmc_cpu_not_0

baremetal/lib/arm.S

@@ -2,6 +2,11 @@
 
 .global lkmc_start
 lkmc_start:
+    /* Make all CPUs except CPU0 sleep by default. */
+    mrc p15, 0, r0, c0, c0, 5
+    ands r0, r0, 3
+    bne lkmc_cpu_not_0
+
     /* Prepare the stack for main, mandatory for C code. */
     ldr sp, =stack_top
 
@@ -28,3 +33,8 @@ lkmc_start:
 
     /* If main returns, exit. */
     bl exit
+
+/* Default action for CPUs besides the first one: sleep forever. */
+LKMC_WEAK(lkmc_cpu_not_0)
+    wfe
+    b lkmc_cpu_not_0

baremetal/lib/syscalls.c

@@ -3,14 +3,6 @@
 #include <sys/stat.h>
 
 #include <lkmc.h>
-#include <lkmc/m5ops.h>
-
-void lkmc_baremetal_on_exit_callback(int status, void *arg) {
-    (void)arg;
-    if (status != 0) {
-        printf("lkmc_exit_status_%d\n", status);
-    }
-}
 
 enum {
     UART_FR_RXFE = 0x10,
@@ -19,44 +11,18 @@ enum {
 #define UART_DR(baseaddr) (*(unsigned int *)(baseaddr))
 #define UART_FR(baseaddr) (*(((unsigned int *)(baseaddr))+6))
 
+void lkmc_baremetal_on_exit_callback(int status, void *arg) {
+    (void)arg;
+    if (status != 0) {
+        printf("lkmc_exit_status_%d\n", status);
+    }
+}
+
 int _close(int file) {
     LKMC_UNUSED(file);
     return -1;
 }
 
-void _exit(int status) {
-    LKMC_UNUSED(status);
-#if LKMC_GEM5
-    LKMC_M5OPS_EXIT;
-#else
-#if defined(__arm__)
-    __asm__ __volatile__ (
-        "mov r0, #0x18\n"
-        "ldr r1, =#0x20026\n"
-        "svc 0x00123456\n"
-        :
-        :
-        : "r0", "r1"
-    );
-#elif defined(__aarch64__)
-    /* TODO actually use the exit value here, just for fun. */
-    __asm__ __volatile__ (
-        "mov x1, #0x26\n" \
-        "movk x1, #2, lsl #16\n" \
-        "str x1, [sp,#0]\n" \
-        "mov x0, #0\n" \
-        "str x0, [sp,#8]\n" \
-        "mov x1, sp\n" \
-        "mov w0, #0x18\n" \
-        "hlt 0xf000\n"
-        :
-        :
-        : "x0", "x1"
-    );
-#endif
-#endif
-}
-
 int _fstat(int file, struct stat *st) {
     LKMC_UNUSED(file);
     st->st_mode = S_IFCHR;

baremetal/lib/syscalls_asm.S

@@ -0,0 +1,35 @@
+#include <lkmc.h>
+
+/* This is implemented in assembly so that it does not use the stack,
+ * and thus can be called safely from programs without the bootloader.
+ * C signature:
+ *
+ * void _exit(int status)
+ *
+ * If only there was a GCC attribute to create such a function!
+ */
+.text
+.global _exit
+_exit:
+#if LKMC_GEM5
+    LKMC_M5OPS_EXIT_ASM
+#else
+/* Use semihosting:
+ * https://github.com/cirosantilli/linux-kernel-module-cheat#semihosting */
+#if defined(__arm__)
+    mov r0, #0x18
+    ldr r1, =#0x20026
+    svc 0x00123456
+#elif defined(__aarch64__)
+    mov x1, 0x26
+    movk x1, 2, lsl 16
+    ldr x2, =.Lsemihost_args
+    str x1, [x2, 0]
+    str x0, [x2, 8]
+    mov x1, x2
+    mov w0, 0x18
+    hlt 0xf000
+.Lsemihost_args:
+    .skip 16
+#endif
+#endif