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 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

(limited to 'sys/arch/amd64')

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)
 {
-- 
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