Add linux-inspired rtc_class_ops struct

.clang-format

@@ -8,11 +8,11 @@ AllowShortFunctionsOnASingleLine: false
 AlwaysBreakTemplateDeclarations: true
 BreakConstructorInitializers: BeforeComma
 AlignConsecutiveDeclarations:
-  Enabled:         true 
+  Enabled:         true
   AcrossEmptyLines: false
   AcrossComments:  false
   AlignCompound:   false
-  AlignFunctionPointers: false
+  AlignFunctionPointers: true
   PadOperators:    false
 AlignConsecutiveMacros: true
 AllowShortCaseLabelsOnASingleLine: true

Makefile

@@ -26,11 +26,13 @@ ASFLAGS = -march=rv64gc -mabi=lp64
 LDFLAGS = -Tkern/kernel.ld
 LDFLAGS += -m elf64lriscv
 
-CFLAGS = -Wall -Werror -O
-CFLAGS += -Wno-unused-result
-CFLAGS += -Wno-unused-variable
+# See: https://gcc.gnu.org/onlinedocs/gcc-14.2.0/gcc/RISC-V-Options.html#index-march-14
 CFLAGS += -mcmodel=medany
 CFLAGS += -march=rv64gc -mabi=lp64
+
+CFLAGS += -Wall -Werror -O
+CFLAGS += -Wno-unused-result
+CFLAGS += -Wno-unused-variable
 CFLAGS += -ffreestanding
 CFLAGS += -fno-common
 CFLAGS += -nostdlib

kern/libkern/badrand.c

@@ -1,4 +1,5 @@
 #include "badrand.h"
+#include "stdio.h"
 #include <stdint.h>
 #include <string.h>
 
@@ -49,4 +50,30 @@ void sbadrand(uint64_t s) {
     }
 }
 
+/* Simple but dumb sanity check for randomness */
+int looks_random(char *buf, size_t len) {
+    int counts[256] = {0};
+    int run = 1, max_run = 1;
+
+    for (size_t i = 0; i < len; i++) {
+        counts[(unsigned int)buf[i]]++;
+        if (i > 0 && buf[i] == buf[i - 1]) {
+            if (++run > max_run)
+                max_run = run;
+        } else {
+            run = 1;
+        }
+    }
+
+    for (int i = 0; i < 256; i++) {
+        if (counts[i] > (int)(len * 1 / 10))
+            return 0;
+    }
+
+    if (max_run > 16)
+        return 0;
+
+    return 1;
+}
+
 #undef PRAND_BUILD_SEED

kern/libkern/badrand.h

@@ -45,4 +45,6 @@ uint64_t badrand_range(uint64_t min, uint64_t max);
  */
 void badrand_buf(char *buf, size_t len);
 
+int looks_random(char *buf, size_t len);
+
 #endif // BADRAND_H

kern/libkern/hexdump.c

@@ -1,5 +1,5 @@
-#include <stddef.h>
 #include <ctype.h>
+#include <stddef.h>
 #include <stdio.h>
 
 void hexdump(const void *data, size_t size) {

kern/rtc.c

@@ -21,12 +21,17 @@ static inline void mmio_write32(uintptr_t addr, uint32_t value) {
     *(volatile uint32_t *)addr = value;
 }
 
-uint64_t rtc_read_time(void) {
+uint64_t rtc_time_read(void) {
     uint32_t low = mmio_read32(VIRT_RTC_BASE + RTC_TIME_LOW);
     uint32_t high = mmio_read32(VIRT_RTC_BASE + RTC_TIME_HIGH);
     return ((uint64_t)high << 32) | low;
 }
 
+void rtc_time_set(uint64_t ns) {
+    mmio_write32(VIRT_RTC_BASE + RTC_TIME_LOW, ns);
+    mmio_write32(VIRT_RTC_BASE + RTC_TIME_HIGH, ns);
+}
+
 void rtc_alarm_set(uint64_t ns) {
     mmio_write32(VIRT_RTC_BASE + RTC_ALARM_HIGH, ns >> 32);
     mmio_write32(VIRT_RTC_BASE + RTC_ALARM_LOW, ns & 0xffffffff);

kern/rtc.h

@@ -3,7 +3,16 @@
 
 #include <stdint.h>
 
-uint64_t rtc_read_time(void);
+struct rtc_class_ops {
+    uint64_t (*read_time)(void);
+    void     (*set_time)(uint64_t);
+    uint64_t (*read_alarm)(uint64_t);
+    void     (*set_alarm)(uint64_t);
+    void     (*alarm_irq_enable)(void);
+};
+
+uint64_t rtc_time_read(void);
+void     rtc_time_set(uint64_t ns);
 
 void     rtc_alarm_set(uint64_t ns);
 uint64_t rtc_alarm_read(void);

kern/start.c

@@ -1,11 +1,11 @@
-#include <endian.h>
-#include <badrand.h>
-#include <hexdump.h>
 #include <assert.h>
+#include <badrand.h>
 #include <banner.h>
 #include <buddy.h>
 #include <config.h>
+#include <endian.h>
 #include <freelist.h>
+#include <hexdump.h>
 #include <memory.h>
 #include <panic.h>
 #include <proc.h>
@@ -49,7 +49,7 @@ void start() {
         memory_sweep(heap_start, heap_end);
         buddy_init(heap_start, heap_end);
         spinlock_init(&sl);
-        sbadrand(rtc_read_time() ^ swap64(rtc_read_time()));
+        sbadrand(rtc_time_read() ^ swap64(rtc_time_read()));
         for (int i = 0; i < banner_len; i++) uart_putc(banner[i]);
         __sync_synchronize();
         hold = 0;
@@ -83,8 +83,8 @@ void start() {
             buddy_free(mem);
         }
         {
-            uint64_t time = rtc_read_time();
-            time = rtc_read_time();
+            uint64_t time = rtc_time_read();
+            time = rtc_time_read();
             rtc_alarm_set(time + 3000000000);
             uint64_t alrm = rtc_alarm_read();
             assert(alrm > time);
@@ -100,8 +100,10 @@ void start() {
         }
         {
             char buffer[128];
+            memset(buffer, 0, 128);
+            assert(!looks_random(buffer, 128));
             badrand_buf(buffer, 128);
-            hexdump(buffer, 128);
+            assert(looks_random(buffer, 128));
         }
 
         kprintf("To exit qemu, press CTRL+a followed by x\n");