From a455da84568992df1e84ba3ff45ff229ecd7c5be Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Fri, 20 Dec 2024 00:28:10 -0500
Subject: kernel/amd64: Add panic backtrace

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/arch/amd64/amd64/machdep.c | 46 ++++++++++++++++++++++++++++++++++++++++++
 sys/include/sys/ksyms.h        | 44 ++++++++++++++++++++++++++++++++++++++++
 sys/include/sys/panic.h        |  1 +
 sys/kern/kern_panic.c          |  3 +++
 4 files changed, 94 insertions(+)
 create mode 100644 sys/include/sys/ksyms.h

(limited to 'sys')

diff --git a/sys/arch/amd64/amd64/machdep.c b/sys/arch/amd64/amd64/machdep.c
index c09ca0e..f74feb1 100644
--- a/sys/arch/amd64/amd64/machdep.c
+++ b/sys/arch/amd64/amd64/machdep.c
@@ -29,6 +29,8 @@
 
 #include <sys/types.h>
 #include <sys/syslog.h>
+#include <sys/ksyms.h>
+#include <sys/panic.h>
 #include <machine/cpu.h>
 #include <machine/gdt.h>
 #include <machine/tss.h>
@@ -108,6 +110,50 @@ try_mitigate_spectre(void)
     ibrs_enable();
 }
 
+static const char *
+backtrace_addr_to_name(uintptr_t addr, off_t *off)
+{
+    uintptr_t prev_addr = 0;
+    const char *name = NULL;
+
+    for (size_t i = 0;;) {
+        if (g_ksym_table[i].addr > addr) {
+            *off = addr - prev_addr;
+            return name;
+        }
+
+        prev_addr = g_ksym_table[i].addr;
+        name = g_ksym_table[i].name;
+        if (g_ksym_table[i++].addr == (uint64_t)-1)
+            break;
+    }
+
+    return NULL;
+}
+
+void
+backtrace(void)
+{
+    uintptr_t *rbp;
+    uintptr_t rip;
+    off_t off;
+    const char *name;
+
+    __ASMV("mov %%rbp, %0" : "=r" (rbp) :: "memory");
+    while (1) {
+        rip = rbp[1];
+        rbp = (uintptr_t *)rbp[0];
+        name = backtrace_addr_to_name(rip, &off);
+
+        if (rbp == NULL)
+            break;
+        if (name == NULL)
+            name = "???";
+
+        kprintf(OMIT_TIMESTAMP "%p  @ <%s+0x%x>\n", rip, name, off);
+    }
+}
+
 void
 cpu_halt_all(void)
 {
diff --git a/sys/include/sys/ksyms.h b/sys/include/sys/ksyms.h
new file mode 100644
index 0000000..2862cbc
--- /dev/null
+++ b/sys/include/sys/ksyms.h
@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _SYS_KSYMS_H_
+#define _SYS_KSYMS_H_
+
+#include <sys/cdefs.h>
+
+#if defined(_KERNEL)
+struct kernel_symbol {
+	uint64_t addr;
+	char* name;
+};
+
+__weak extern struct kernel_symbol g_ksym_table[];
+
+#endif  /* defined(_KERNEL) */
+#endif
diff --git a/sys/include/sys/panic.h b/sys/include/sys/panic.h
index d3e6211..9db6a1e 100644
--- a/sys/include/sys/panic.h
+++ b/sys/include/sys/panic.h
@@ -33,6 +33,7 @@
 #if defined(_KERNEL)
 
 void panic(const char *fmt, ...);
+void backtrace(void);
 
 #endif  /* _KERNEL */
 #endif  /* !_SYS_PANIC_H_ */
diff --git a/sys/kern/kern_panic.c b/sys/kern/kern_panic.c
index 0a17456..af154a8 100644
--- a/sys/kern/kern_panic.c
+++ b/sys/kern/kern_panic.c
@@ -53,6 +53,9 @@ panic(const char *fmt, ...)
     kprintf(OMIT_TIMESTAMP "panic: ");
     vkprintf(fmt, &ap);
 
+    kprintf(OMIT_TIMESTAMP "** backtrace\n");
+    backtrace();
+
     cpu_reboot(REBOOT_HALT);
     __builtin_unreachable();
 }
-- 
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