From 0a817a5a74c328229f8a732fc3ec22d8fd7dc20d Mon Sep 17 00:00:00 2001
From: Peter Mikkelsen <petermikkelsen10@gmail.com>
Date: Tue, 29 Jul 2025 21:40:45 +0200
Subject: Some work on keeping track of memory, and providing more info in
 panics

---
 src/aplos.h  |  39 ++++++++++++-
 src/main.c   |  57 +-----------------
 src/nasty.S  |  41 +++++++++++++
 src/paging.c | 185 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/panic.c  |  11 ++++
 src/screen.c |   3 +
 6 files changed, 280 insertions(+), 56 deletions(-)

(limited to 'src')

diff --git a/src/aplos.h b/src/aplos.h
index 7d3fce0..ad9109b 100644
--- a/src/aplos.h
+++ b/src/aplos.h
@@ -29,6 +29,40 @@ struct boot_info
 	uint64_t physbase;
 };
 
+struct cpu_regs
+{
+	/* Keep this in sync with dump_regs in nasty.S */
+	uint64_t rax;
+	uint64_t rbx;
+	uint64_t rcx;
+	uint64_t rdx;
+	uint64_t rsi;
+	uint64_t rdi;
+	uint64_t rsp;
+	uint64_t rbp;
+	uint64_t r8;
+	uint64_t r9;
+	uint64_t r10;
+	uint64_t r11;
+	uint64_t r12;
+	uint64_t r13;
+	uint64_t r14;
+	uint64_t r15;
+	uint64_t rip;
+	uint64_t rflags;
+	uint64_t cr0;
+	uint64_t cr2;
+	uint64_t cr3;
+	uint64_t cr4;
+	uint64_t cr8;
+	uint16_t cs;
+	uint16_t ds;
+	uint16_t ss;
+	uint16_t es;
+	uint16_t fs;
+	uint16_t gs;
+};
+
 /* boot.c */
 uint64_t cpu_count(void);
 
@@ -47,7 +81,7 @@ void main(struct boot_info *);
 
 /* nasty.S */
 struct table_reg;
-void halt(void);
+[[noreturn]] void halt(void);
 void disable_interrupts(void);
 void enable_interrupts(void);
 void set_gdt(struct table_reg *, uint64_t, uint64_t, uint64_t);
@@ -55,13 +89,14 @@ void set_idt(struct table_reg *);
 uint64_t get_cr2(void);
 uint64_t get_cr3(void);
 extern void (*isr_stubs[32])(void);
+void dump_regs(struct cpu_regs *);
 
 /* paging.c */
 void setup_paging(struct boot_info *);
 bool page_fault_handler(uint32_t);
 
 /* panic.c */
-void panic(void);
+[[noreturn]] void panic(void);
 
 /* screen.c */
 void screen_init(struct framebuffer *);
diff --git a/src/main.c b/src/main.c
index 03ad3fd..a3b7719 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,66 +1,15 @@
 #include "aplos.h"
 
-static void welcome(void);
-static void print_memmap(struct boot_info *);
-static void print_size(uint64_t);
-
 void
 main(struct boot_info *info)
 {
 	screen_init(&info->framebuffer);
-	welcome();
+	print(u8"Starting ☺☻☺☻☺☻☺☻☺☻\n");
 	print(u8"CPU count: %u64\n", cpu_count());
-	print_memmap(info);
 
 	setup_descriptors();
 	setup_paging(info);
-}
-
-static void
-welcome(void)
-{
-	print(u8"Starting ☺☻☺☻☺☻☺☻☺☻\n");
-}
-
-static void
-print_memmap(struct boot_info *info)
-{
-	print(u8"Usable memory: ");
-	uint64_t total = 0;
-	for(uint64_t i = 0; i < info->memmap_count; i++)
-		total += info->memmaps[i].size;
-	print_size(total);
-	print(u8"\n");
-
-	for(uint64_t i = 0; i < info->memmap_count; i++){
-		struct memmap *m = &info->memmaps[i];
-		print(u8"%p - %p (", m->start, m->start + m->size);
-		print_size(m->size);
-		print(u8")\n");
-	}
-}
-
-static void
-print_size(uint64_t size)
-{
-	uint64_t gb, mb, kb, b;
-	gb = size >> 30; size -= gb << 30;
-	mb = size >> 20; size -= mb << 20;
-	kb = size >> 10; size -= kb << 10;
-	b  = size;
-
-	int printed = 0;
-
-#define P(what, spec, force)			\
-	if(what || (force && !printed)){			\
-		if(printed)			\
-			print(u8" + ");		\
-		printed = 1;			\
-		print(u8"%u64 " spec, what);	\
-	}
 
-	P(gb, "GB", 0);
-	P(mb, "MB", 0);
-	P(kb, "KB", 0);
-	P(b, "B", 1);
+	int *x = (int*)0xBEEF;
+	*x = 4; /* This should give us a page fault, and trigger the panic function */
 }
diff --git a/src/nasty.S b/src/nasty.S
index 9fdab5f..f3d958e 100644
--- a/src/nasty.S
+++ b/src/nasty.S
@@ -106,3 +106,44 @@ DEFINE_ISRS
 isr_stubs:
 DEFINE_ISRS
 #undef ISR
+
+.section .text
+.global dump_regs
+dump_regs:
+	mov [rdi+0], rax
+	mov [rdi+8], rbx
+	mov [rdi+16], rcx
+	mov [rdi+24], rdx
+	mov [rdi+32], rsi
+	mov [rdi+40], rdi
+	mov [rdi+48], rsp
+	mov [rdi+56], rbp
+	mov [rdi+64], r8
+	mov [rdi+72], r9
+	mov [rdi+80], r10
+	mov [rdi+88], r11
+	mov [rdi+96], r12
+	mov [rdi+104], r13
+	mov [rdi+112], r14
+	mov [rdi+120], r15
+	lea rax, [rip]
+	mov [rdi+128], rax
+	pushf
+	pop [rdi+136]
+	mov rax, cr0
+	mov [rdi+144], rax
+	mov rax, cr2
+	mov [rdi+152], rax
+	mov rax, cr3
+	mov [rdi+160], rax
+	mov rax, cr4
+	mov [rdi+168], rax
+	mov rax, cr8
+	mov [rdi+176], rax
+	mov [rdi+184], cs
+	mov [rdi+186], ds
+	mov [rdi+188], ss
+	mov [rdi+190], es
+	mov [rdi+192], fs
+	mov [rdi+194], gs
+	ret
diff --git a/src/paging.c b/src/paging.c
index 0728178..ecbd647 100644
--- a/src/paging.c
+++ b/src/paging.c
@@ -1,9 +1,50 @@
 #include "aplos.h"
 
+#define MAX_REGIONS 1024
+#define INVALID_PTR UINT64_MAX
+
+struct region
+{
+	uint64_t start;
+	uint64_t size;
+	uint64_t next;
+	int available : 1;
+};
+
+struct region_map
+{
+	uint64_t used;   /* Chain of used indices in the regions table */
+	uint64_t unused; /* Chain of unused indices in the regions table */
+	struct region regions[MAX_REGIONS];
+};
+
+static struct region_map physical;
+static struct region_map virtual;
+
+static void init_map(struct region_map *, bool);
+static void mark_region(struct region_map *, uint64_t, uint64_t, bool);
+static uint64_t lookup(struct region_map *, uint64_t);
+static void delete_node(struct region_map *, uint64_t);
+static uint64_t add_node(struct region_map *, uint64_t, uint64_t, bool);
+static void debug_region_map(struct region_map *);
+static void print_size(uint64_t);
+
 void
 setup_paging(struct boot_info *info)
 {
 	print(u8"Setting up paging. All usable physical memory is mapped starting at %p\n", info->physbase);
+
+	init_map(&physical, false);
+	init_map(&virtual, true);
+
+	for(uint64_t i = 0; i < info->memmap_count; i++)
+		mark_region(&physical, info->memmaps[i].start, info->memmaps[i].size, true);
+	debug_region_map(&physical);
+
+	/* TODO fill in the used regions of virtual memory, by inspection the page tables that was setup for us
+	 * by the bootloader.
+	 */
+
 	uint64_t cr3 = get_cr3();
 	print(u8"CR3: %p\n", cr3);
 }
@@ -18,3 +59,147 @@ page_fault_handler(uint32_t code)
 
 	return false; /* We didn't actually handle it */
 }
+
+static void
+init_map(struct region_map *map, bool available)
+{
+	map->used = INVALID_PTR;
+	map->unused = 0;
+
+	for(uint64_t p = 0; p < MAX_REGIONS-1; p++)
+		map->regions[p].next = p+1;
+	map->regions[MAX_REGIONS-1].next = INVALID_PTR;
+
+	add_node(map, 0, UINT64_MAX, available);
+}
+
+static void
+mark_region(struct region_map *map, uint64_t addr, uint64_t size, bool available)
+{
+	uint64_t p = lookup(map, addr);
+	struct region *r = &map->regions[p];
+
+	if((r->start <= addr) && (r->start+r->size >= addr+size) && (r->available != available)){
+		/* Entirely within a current region. Split the current one up. */
+		uint64_t oldstart = r->start;
+		uint64_t oldend = r->start+r->size;
+		delete_node(map, p);
+		add_node(map, oldstart, addr - r->start, !available);
+		add_node(map, addr, size, available);
+		add_node(map, addr+size, oldend-(addr+size), !available);
+	}else
+		panic(); /* I don't want to think about this right now */
+}
+
+static uint64_t
+lookup(struct region_map *map, uint64_t addr)
+{
+	uint64_t p;
+	struct region *r;
+
+	for(p = map->used; p != INVALID_PTR; p = r->next){
+		r = &map->regions[p];
+		if((r->start <= addr) && (r->start+r->size > addr))
+			return p;
+	}
+	panic();
+}
+
+static void
+delete_node(struct region_map *map, uint64_t p)
+{
+	uint64_t x;
+	uint64_t prev = INVALID_PTR;
+	for(x = map->used; x != INVALID_PTR; prev = x, x = map->regions[x].next){
+		if(x == p){
+			if(prev != INVALID_PTR)
+				map->regions[prev].next = map->regions[x].next;
+			else
+				map->used = INVALID_PTR;
+			map->regions[x].next = map->unused;
+			map->unused = x;
+			return;
+		}
+	}
+	panic();
+}
+
+static uint64_t
+add_node(struct region_map *map, uint64_t start, uint64_t size, bool available)
+{
+	struct region *r;
+	uint64_t p;
+	uint64_t prev = INVALID_PTR;
+	for(p = map->used; p != INVALID_PTR; prev = p, p = map->regions[p].next){
+		if(map->regions[p].start > start)
+			break;
+	}
+
+	uint64_t new = map->unused;
+
+	if(prev == INVALID_PTR){
+		r = &map->regions[map->unused];
+		uint64_t tmp = map->used;
+		map->used = map->unused;
+		map->unused = r->next;
+		r->next = tmp;
+	}else{
+		r = &map->regions[map->unused];
+		map->unused = r->next;
+		r->next = map->regions[prev].next;
+		map->regions[prev].next = new;
+	}
+
+	r->start = start;
+	r->size = size;
+	r->available = available;
+	return new;
+}
+
+static void
+debug_region_map(struct region_map *map)
+{
+	uint64_t available = 0;
+	for(uint64_t p = map->used; p != INVALID_PTR; p = map->regions[p].next){
+		struct region *r = &map->regions[p];
+		if(r->available)
+			available += r->size;
+	}
+	print(u8"Total available memory: ");
+	print_size(available);
+	print(u8"\n");
+
+	for(uint64_t p = map->used; p != INVALID_PTR; p = map->regions[p].next){
+		struct region *r = &map->regions[p];
+		if(r->available){
+			print(u8"[%p - %p] (", r->start, r->start+r->size);
+			print_size(r->size);
+			print(u8")\n");
+		}
+	}
+}
+
+static void
+print_size(uint64_t size)
+{
+        uint64_t gb, mb, kb, b;
+        gb = size >> 30; size -= gb << 30;
+        mb = size >> 20; size -= mb << 20;
+        kb = size >> 10; size -= kb << 10;
+        b  = size;
+
+        int printed = 0;
+
+#define P(what, spec, force)                    \
+        if(what || (force && !printed)){                        \
+                if(printed)                     \
+                        print(u8" + ");         \
+                printed = 1;                    \
+                print(u8"%u64 " spec, what);    \
+        }
+
+        P(gb, "GB", 0);
+        P(mb, "MB", 0);
+        P(kb, "KB", 0);
+        P(b, "B", 1);
+}
diff --git a/src/panic.c b/src/panic.c
index 5b17b04..3b39aeb 100644
--- a/src/panic.c
+++ b/src/panic.c
@@ -3,6 +3,17 @@
 void
 panic(void)
 {
+	struct cpu_regs r;
+	dump_regs(&r);
+
 	print(u8"--- PANIC ---\n");
+	print(u8"rax: %p rbx: %p rcx: %p rdx: %p\n", r.rax, r.rbx, r.rcx, r.rdx);
+	print(u8"rsi: %p rdi: %p rsp: %p rbp: %p\n", r.rsi, r.rdi, r.rsp, r.rbp);
+	print(u8"r8:  %p r9:  %p r10: %p r11: %p\n", r.r9, r.r9, r.r10, r.r11);
+	print(u8"r12: %p r13: %p r14: %p r15: %p\n", r.r12, r.r13, r.r14, r.r15);
+	print(u8"rip: %p cr0: %p cr2: %p cr3: %p\n", r.rip, r.cr0, r.cr2, r.cr3);
+	print(u8"cr4: %p cr8: %p cs:  %p ds:  %p\n", r.cr4, r.cr8, r.cs, r.ds);
+	print(u8"ss:  %p es:  %p fs:  %p gs:  %p\n", r.ss, r.es, r.fs, r.gs);
+	print(u8"rflags: %p\n", r.rflags);
 	halt();
 }
diff --git a/src/screen.c b/src/screen.c
index 903ce9c..46f1231 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -48,6 +48,9 @@ print_char:
 			row++;
 			col = 0;
 			break;
+		case '\t':
+			col = (col+8) & ~7;
+			break;
 		case '%':
 			n = print_fmt(p, args);
 			if(n == 0)
-- 
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