added backtraces

include/backtrace.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include <stddef.h>
+
+// Fill dst with a stack trace consisting of return addresses
+// in order from top to bottom. returns the number filled (at most len)
+size_t backtrace(void **dst, size_t len);
+
+
+// same as backtrace but with specified instruction and base pointer
+size_t backtrace_ex(void **dst, size_t len, void* ip, void *bp);
+
+// TODO symbols
+//size_t backtrace_symbols(char *const *dst, size_t len);
+
+// Log a backtrace
+void log_backtrace();
+
+// same as log_backtrace with specified insruction and base pointer
+void log_backtrace_ex(void *ip, void *bp);

include/panic.h

@@ -6,3 +6,5 @@
 #define panic(msg) _panic_impl(_PANIC_STR(__LINE__), __FILE__, msg)
 
 _Noreturn void _panic_impl(char *line, char *file, char *msg);
+
+_Noreturn void panic_interrupt(void *ip, void *bp, char *msg);

src/arch/amd64/backtrace.c

@@ -0,0 +1,53 @@
+#include <backtrace.h>
+#include <lib.h>
+#include "serial.h"
+
+struct stackframe {
+	struct stackframe *rbp;
+	void *rip;
+};
+
+size_t backtrace(void **dst, size_t len) {
+	struct stackframe *rbp;
+	__asm__ volatile ("mov %%rbp, %0" : "=r"(rbp));
+	return backtrace_ex(dst, len, rbp->rip, rbp->rbp);
+}
+
+size_t backtrace_ex(void **dst, size_t len, void *ip, void *bp) {
+	struct stackframe *frame = bp;
+	__asm__ volatile ("mov %%rbp, %0" : "=r"(frame));
+	if(len > 0) {
+		dst[0] = ip;
+	}
+	size_t i;
+	for(i = 1; frame && i < len; i++) {
+		dst[i] = frame->rip;
+		frame = frame->rbp;
+	}
+	return i;
+}
+
+void log_backtrace() {
+	struct stackframe *rbp;
+	__asm__ volatile ("mov %%rbp, %0" : "=r"(rbp));
+	log_backtrace_ex(rbp->rip, rbp->rbp);
+}
+
+
+void log_backtrace_ex(void *ip, void *bp) {
+	struct stackframe *frame = bp;
+	char buf[20];
+	serial_out_str("Stack trace:\n");
+	ultoa((size_t)ip, buf, 16);
+	serial_out_str("  0x");
+	serial_out_str(buf);
+	serial_out_str("\n");
+	while(frame) {
+		ultoa((size_t)frame->rip, buf, 16);
+		serial_out_str("  0x");
+		serial_out_str(buf);
+		serial_out_str("\n");
+		frame = frame->rbp;
+	}
+
+}

src/arch/amd64/boot.S

@@ -136,13 +136,16 @@ start:
 	bits 64
 code64:
 
-	mov dx, 16
-	mov ds, dx
+	mov dx, 16            ; set segment registers
+	mov ds, dx            ; so that interrupts work
 	mov ss, dx
 
+	xor rbp, rbp          ; set ebp to 0 so we know where to end stack traces
+
 	pop rdi
 	call amd64_shim
 	mov rdi, rax
+
 	sti
 	call kmain
 	cli

src/arch/amd64/idt.S

@@ -49,8 +49,10 @@ align 8
 isr_stub_%+%1:
     PUSHALL
     cld
-    mov rdi, %1
-    mov rsi, 0
+    mov rdi, %1                  ; exception number
+    mov rsi, 0                   ; placeholder error code
+    mov rdx, [rsp + 15 * 8]      ; instruction pointer
+    mov rcx, rbp                 ; base pointer for stack trace
     call idt_exception_handler
     POPALL
     iretq
@@ -64,10 +66,13 @@ align 8
 isr_stub_%+%1:
     PUSHALL
     cld
-    mov rdi, %1
-    pop rsi
+    mov rdi, %1                  ; exception number
+    mov rsi, [rsp + 15 * 8]      ; error code
+    mov rdx, [rsp + 16 * 8]      ; instruction pointer
+    mov rcx, rbp                 ; base pointer for stack trace
     call idt_exception_handler
     POPALL
+    sub rsp, 8                   ; discard error code
     iretq
 %endmacro
 

src/arch/amd64/idt.c

@@ -4,6 +4,7 @@
 #include <lib.h>
 #include <serial.h>
 
+#include "backtrace.h"
 #include "idt.h"
 #include "pic.h"
 
@@ -107,7 +108,7 @@ char *EXCEPTIONS[] = {
 	"0x1F Reserved",
 };
 
-void idt_exception_handler(uint64_t exception, uint64_t code) {
+void idt_exception_handler(uint64_t exception, uint64_t code, void *rip, void *rbp) {
 	// TODO don't just panic
 	char buf[24];
 	char msg[256] = "Exception ";
@@ -127,7 +128,7 @@ void idt_exception_handler(uint64_t exception, uint64_t code) {
 		strcat(msg, buf);
 	}
 
-	panic(msg);
+	panic_interrupt(rip, rbp, msg);
 }
 
 void idt_pic_eoi(uint8_t exception) {

src/arch/amd64/panic.c

@@ -1,4 +1,5 @@
 #include <panic.h>
+#include <backtrace.h>
 
 #include "serial.h"
 #include "bindings.h"
@@ -12,7 +13,19 @@ _Noreturn void _panic_impl(char *line, char *file, char *msg) {
 	serial_out_str(line);
 	serial_out_str(":\n");
 	serial_out_str(msg);
-	serial_out('\n');
+	serial_out_str("\n\n");
+	log_backtrace();
+	while (1) {
+		halt();
+	}
+}
+
+_Noreturn void panic_interrupt(void *ip, void *bp, char *msg) {
+	cli();
+	serial_out_str("\n\n!!! PANIC !!!\n");
+	serial_out_str(msg);
+	serial_out_str("\n\n");
+	log_backtrace_ex(ip, bp);
 	while (1) {
 		halt();
 	}

src/kmain.c

@@ -4,6 +4,30 @@
 #include <fb.h>
 #include <shim.h>
 
+void print_memory() {
+	size_t WIDTH = 64;
+
+	for(size_t i = 0;; i += WIDTH) {
+		char buf[20];
+		ultoa(i, buf, 16);
+		serial_out_str("0x");
+		for(size_t k = 0; k < 6 - strlen(buf); k++) {
+			serial_out('0');
+		}
+		serial_out_str(buf);
+		serial_out_str(": ");
+		for(size_t j = 0; j < WIDTH; j++) {
+			char x = *(char *)(i + j);
+			if(x < 0x20 || x >= 0x7f) {
+				serial_out('.');
+			} else {
+				serial_out(x);
+			}
+		}
+		serial_out('\n');
+	}
+}
+
 void kmain(struct boot_info *info) {
 	memory_init(info->map);
 	serial_out_str("entered kmain\n");