Improve debugging functions

- More sensible stack tracer, in C++ (no symbols yet)
- Was forgetting to add null frame to new kernel stacks
- __kernel_assert was using an old vector
- A GP fault will only print its associated table entry

scripts/templates/build.ninja.j2

@@ -136,6 +136,10 @@ rule strip
         strip -g $out; $
         objcopy --add-gnu-debuglink=$out.debug $out
 
+rule dump
+    description = Dumping decompiled $name
+    command = objdump -DS $in > $out
+
 
 {% for target in targets %}
 subninja {{ target }}/target.ninja
@@ -161,6 +165,9 @@ build $builddir/ovmf_vars_d.fd : cp $srcroot/assets/ovmf/x64/ovmf_vars_d.fd
 build $builddir/popcorn.elf | $builddir/popcorn.elf.debug : strip $builddir/host/popcorn.elf
     name = kernel
 
+build $builddir/popcorn.dump : dump $builddir/host/popcorn.elf
+    name = kernel
+
 build $builddir/popcorn.elf-gdb.py : cp ${srcroot}/assets/debugging/popcorn.elf-gdb.py
     name = kernel debug python scripts
 

src/kernel/assert.cpp

@@ -8,13 +8,14 @@ __kernel_assert(const char *file, unsigned line, const char *message)
 	if (cons) {
 		cons->set_color(9 , 0);
 		cons->puts("\n\n       ERROR: ");
+		cons->puts(message);
+		cons->puts("\n              ");
 		cons->puts(file);
 		cons->puts(":");
 		cons->put_dec(line);
-		cons->puts(":  ");
+		cons->puts("\n");
-		cons->puts(message);
 	}
 
-	__asm__ ( "int $0e7h" );
+	__asm__ ( "int $0e4h" );
 	while (1) __asm__ ("hlt");
 }

src/kernel/debug.cpp

@@ -4,7 +4,9 @@
 #include "gdt.h"
 #include "page_manager.h"
 
-#define print_reg(name, value) cons->printf("         %s: %016lx\n", name, (value));
+#define print_regL(name, value) cons->printf("       %s: %016lx", name, (value));
+#define print_regM(name, value) cons->printf("    %s: %016lx", name, (value));
+#define print_regR(name, value) cons->printf("    %s: %016lx\n", name, (value));
 
 size_t __counter_syscall_enter = 0;
 size_t __counter_syscall_sysret = 0;
@@ -14,48 +16,52 @@ print_regs(const cpu_state &regs)
 {
 	console *cons = console::get();
 
-	print_reg("rax", regs.rax);
+	print_regL("rax", regs.rax);
-	print_reg("rbx", regs.rbx);
+	print_regM("rbx", regs.rbx);
-	print_reg("rcx", regs.rcx);
+	print_regR("rcx", regs.rcx);
-	print_reg("rdx", regs.rdx);
+	print_regL("rdx", regs.rdx);
-	print_reg("rdi", regs.rdi);
+	print_regM("rdi", regs.rdi);
-	print_reg("rsi", regs.rsi);
+	print_regR("rsi", regs.rsi);
 
 	cons->puts("\n");
-	print_reg(" r8", regs.r8);
+	print_regL(" r8", regs.r8);
-	print_reg(" r9", regs.r9);
+	print_regM(" r9", regs.r9);
-	print_reg("r10", regs.r10);
+	print_regR("r10", regs.r10);
-	print_reg("r11", regs.r11);
+	print_regL("r11", regs.r11);
-	print_reg("r12", regs.r12);
+	print_regM("r12", regs.r12);
-	print_reg("r13", regs.r13);
+	print_regR("r13", regs.r13);
-	print_reg("r14", regs.r14);
+	print_regL("r14", regs.r14);
-	print_reg("r15", regs.r15);
+	print_regM("r15", regs.r15);
 
-	cons->puts("\n");
+	cons->puts("\n\n");
-	print_reg("rbp", regs.rbp);
+	print_regL("rbp", regs.rbp);
-	print_reg("rsp", regs.user_rsp);
+	print_regM("rsp", regs.user_rsp);
-	print_reg("sp0", tss_get_stack(0));
+	print_regR("sp0", tss_get_stack(0));
 
-	cons->puts("\n");
+	print_regL("rip", regs.rip);
-	print_reg(" cs", regs.cs);
+	print_regM("cr3", page_manager::get()->get_pml4());
-	print_reg(" ss", regs.ss);
+	cons->puts("\n\n");
-
-	cons->puts("\n");
-	print_reg("rip", regs.rip);
-
-	cons->puts("\n");
-	print_reg("cr3", page_manager::get()->get_pml4());
 }
 
+struct frame
+{
+	frame *prev;
+	uintptr_t return_addr;
+};
+
 void
 print_stacktrace(int skip)
 {
 	console *cons = console::get();
-	int frame = 0;
+
-	uint64_t bp = get_frame(skip);
+	frame *fp = nullptr;
-	while (bp) {
+	int fi = -skip;
-		cons->printf("    frame %2d: %lx\n", frame, bp);
+	__asm__ __volatile__ ( "mov %%rbp, %0" : "=r" (fp) );
-		bp = get_frame(++frame + skip);
+
+	while (fp) {
+		if (fi++ >= 0)
+			cons->printf("  frame %2d: %lx\n", fi-1, fp->return_addr);
+		fp = fp->prev;
 	}
 }
 

src/kernel/debug.h

@@ -9,7 +9,6 @@ extern "C" {
 	uintptr_t get_rip();
 	uintptr_t get_frame(int frame);
 	uintptr_t get_gsbase();
-
 }
 
 extern size_t __counter_syscall_enter;
@@ -17,7 +16,7 @@ extern size_t __counter_syscall_sysret;
 
 void print_regs(const cpu_state &regs);
 void print_stack(const cpu_state &regs);
-void print_stacktrace(int skip = 0);
+void print_stacktrace(int skip);
 
 #define print_reg(name, value) cons->printf("         %s: %016lx\n", name, (value));
 

src/kernel/debug.s

@@ -18,19 +18,3 @@ _halt:
 	hlt
 	jmp _halt
 
-
-global get_frame
-get_frame:
-	mov rcx, rbp
-
-.loop:
-	mov rax, [rcx + 8]
-	mov rcx, [rcx]
-	cmp rdi, 0
-	je .done
-
-	sub rdi, 1
-	jmp .loop
-
-.done:
-	ret

src/kernel/gdt.cpp

@@ -184,18 +184,25 @@ gdt_init()
 }
 
 void
-gdt_dump()
+gdt_dump(int index)
 {
 	const table_ptr &table = g_gdtr;
 
 	console *cons = console::get();
-	cons->printf("         GDT: loc:%lx size:%d\n", table.base, table.limit+1);
 
+	int start = 0;
 	int count = (table.limit + 1) / sizeof(gdt_descriptor);
+	if (index != -1) {
+		start = index;
+		count = 1;
+	} else {
+		cons->printf("         GDT: loc:%lx size:%d\n", table.base, table.limit+1);
+	}
+
 	const gdt_descriptor *gdt =
 		reinterpret_cast<const gdt_descriptor *>(table.base);
 
-	for (int i = 0; i < count; ++i) {
+	for (int i = start; i < start+count; ++i) {
 		uint32_t base =
 			(gdt[i].base_high << 24) |
 			(gdt[i].base_mid << 16) |
@@ -233,17 +240,25 @@ gdt_dump()
 }
 
 void
-idt_dump()
+idt_dump(int index)
 {
 	const table_ptr &table = g_idtr;
 
-	log::info(logs::boot, "Loaded IDT at: %lx size: %d bytes", table.base, table.limit+1);
 
+	int start = 0;
 	int count = (table.limit + 1) / sizeof(idt_descriptor);
+	if (index != -1) {
+		start = index;
+		count = 1;
+		log::info(logs::boot, "IDT FOR INDEX %02x", index);
+	} else {
+		log::info(logs::boot, "Loaded IDT at: %lx size: %d bytes", table.base, table.limit+1);
+	}
+
 	const idt_descriptor *idt =
 		reinterpret_cast<const idt_descriptor *>(table.base);
 
-	for (int i = 0; i < count; ++i) {
+	for (int i = start; i < start+count; ++i) {
 		uint64_t base =
 			(static_cast<uint64_t>(idt[i].base_high) << 32) |
 			(static_cast<uint64_t>(idt[i].base_mid)  << 16) |

src/kernel/gdt.h

@@ -25,7 +25,9 @@ void tss_set_stack(int ring, uintptr_t rsp);
 uintptr_t tss_get_stack(int ring);
 
 /// Dump information about the current GDT to the screen
-void gdt_dump();
+/// \arg index  Which entry to print, or -1 for all entries
+void gdt_dump(int index = -1);
 
 /// Dump information about the current IDT to the screen
-void idt_dump();
+/// \arg index  Which entry to print, or -1 for all entries
+void idt_dump(int index = -1);

src/kernel/interrupts.cpp

@@ -124,13 +124,13 @@ isr_handler(uintptr_t return_rsp, cpu_state *regs)
 				switch ((regs->errorcode & 0x07) >> 1) {
 				case 0:
 					cons->printf(" GDT[%x]\n", index);
-					gdt_dump();
+					gdt_dump(index);
 					break;
 
 				case 1:
 				case 3:
 					cons->printf(" IDT[%x]\n", index);
-					idt_dump();
+					idt_dump(index);
 					break;
 
 				default:

src/kernel/scheduler.cpp

@@ -143,8 +143,9 @@ scheduler::load_process(const char *name, const void *data, size_t size)
 	// Create a one-page kernel stack space
 	void *stack0 = proc->setup_kernel_stack(stack_size, 0);
 
-	// Stack grows down, point to the end
+	// Stack grows down, point to the end, resere space for initial null frame
-	void *sp0 = kutil::offset_pointer(stack0, stack_size);
+	static const size_t null_frame = sizeof(uint64_t);
+	void *sp0 = kutil::offset_pointer(stack0, stack_size - null_frame);
 
 	cpu_state *state = reinterpret_cast<cpu_state *>(sp0) - 1;