From 5481848e27fdd4fc859def9841a0283665531a46 Mon Sep 17 00:00:00 2001
From: Benji Dial <benji6283@gmail.com>
Date: Sun, 13 Sep 2020 17:12:29 -0400
Subject: fixed some paging bugs, added fault handlers and new programs

---
 src/kernel/elf.c               | 14 ++++++++
 src/kernel/fat.c               | 15 ++++++---
 src/kernel/idt.c               | 54 +++++++++++++++++++++++++++++--
 src/kernel/isrs.asm            | 73 ++++++++++++++++++++++++++++++++++++++++--
 src/kernel/main.c              |  2 +-
 src/kernel/paging.c            | 53 +++++++++++++-----------------
 src/kernel/paging.h            |  4 ---
 src/kernel/pmap.c              | 31 ++++++++++++++++--
 src/kernel/task.c              |  2 ++
 src/kernel/task.h              |  5 ++-
 src/kernel/vga.c               |  2 ++
 src/user/dumphex/dumphex.c     | 29 +++++++++++++++++
 src/user/dumptext/dumptext.c   | 15 +++++++++
 src/user/hello/hello.asm       | 14 ++++++++
 src/user/highway/highway.c     |  7 +++-
 src/user/include/knob/format.h |  2 ++
 src/user/init/init.c           | 15 +++++----
 src/user/knob/entry.asm        |  1 -
 src/user/knob/format.c         | 14 ++++++++
 src/user/knob/user.c           | 14 +++++---
 20 files changed, 307 insertions(+), 59 deletions(-)
 create mode 100644 src/user/dumphex/dumphex.c
 create mode 100644 src/user/dumptext/dumptext.c
 create mode 100644 src/user/hello/hello.asm

(limited to 'src')

diff --git a/src/kernel/elf.c b/src/kernel/elf.c
index 423d51a..07cff91 100644
--- a/src/kernel/elf.c
+++ b/src/kernel/elf.c
@@ -126,6 +126,20 @@ bool try_elf_run(const struct drive *d, const char *path, const char *pass_old_v
   tstate.page_directory = pd;
   tstate.ret_addr = ehead.entry_vma;
   tstate.edx = (uint32_t)pass_vma;
+
+  const char *path_end_start = path;
+  for (const char *i = path; *i; ++i)
+    if (*i == '/')
+      path_end_start = i + 1;
+
+  uint8_t i;
+  for (i = 0; i < TASK_NAME_LEN; ++i) {
+    if (!path_end_start[i])
+      break;
+    tstate.name[i] = path_end_start[i];
+  }
+  tstate.name[i] = '\0';
+
   new_task(tstate);
   return true;
 }
\ No newline at end of file
diff --git a/src/kernel/fat.c b/src/kernel/fat.c
index c297cab..c4461de 100644
--- a/src/kernel/fat.c
+++ b/src/kernel/fat.c
@@ -119,10 +119,17 @@ static const uint8_t this_dir[]   = {'.', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' '
 static const uint8_t parent_dir[] = {'.', '.', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' '};
 
 static inline bool check_fat_names(const uint8_t *a, const uint8_t *b) {
-  return (((uint32_t *)a)[0] == ((uint32_t *)b)[0]) &&
-         (((uint32_t *)a)[1] == ((uint32_t *)b)[1]) &&
-         (((uint16_t *)a)[4] == ((uint16_t *)b)[4]) &&
-         (((uint8_t *)a)[10] == ((uint8_t *)b)[10]);
+  for (uint8_t i = 0; i < 11; ++i) {
+    uint8_t ac = a[i];
+    uint8_t bc = b[i];
+    if ((ac >= 0x61) && (ac <= 0x7a))
+      ac &= ~0x20;
+    if ((bc >= 0x61) && (bc <= 0x7a))
+      bc &= ~0x20;
+    if (ac != bc)
+      return false;
+  }
+  return true;
 }
 
 //after: cur_dir -> specified entry in root
diff --git a/src/kernel/idt.c b/src/kernel/idt.c
index 4dc8a36..b789d42 100644
--- a/src/kernel/idt.c
+++ b/src/kernel/idt.c
@@ -103,8 +103,8 @@ void const *syscall_table[] = {
   &sc_memory_info
 };
 
-//these aren't really void (*)()'s, but gcc complains if we take an address of a void, so we give it a type
-typedef void (*isr_t)();
+//these aren't really void ()'s, but gcc complains if we take an address of a void, so we give it a type
+typedef void isr_t();
 
 extern isr_t syscall_isr;
 extern isr_t quit_isr;
@@ -112,6 +112,48 @@ extern isr_t yield_isr;
 
 extern isr_t kbd_isr;
 
+extern isr_t udf_isr;
+extern isr_t dfa_isr;
+extern isr_t tsf_isr;
+extern isr_t npf_isr;
+extern isr_t ssf_isr;
+extern isr_t gpf_isr;
+extern isr_t pff_isr;
+
+__attribute__ ((noreturn))
+void exception_halt(const char *id, uint32_t code, uint32_t eip, uint32_t cs) {
+  char nbuf[11];
+
+  set_log_mode(LOG_PANIC);
+  logsz("Exception #");
+  logsz(id);
+  logsz(" at 0x");
+  u8_hex(cs, nbuf);
+  logsz(nbuf);
+  logsz(":0x");
+  u32_hex(eip, nbuf);
+  logsz(nbuf);
+
+  logsz("\nerror code = 0x");
+  u32_hex(code, nbuf);
+  logsz(nbuf);
+
+  logsz("\ntask name = ");
+  logsz(active_task->name);
+
+  logsz("\ncr3 = 0x");
+  uint32_t cr3;
+  asm (
+    "mov %%cr3, %0"
+  : "=r" (cr3));
+  u32_hex(cr3, nbuf);
+  logsz(nbuf);
+
+  logsz("\nHalting.");
+  while (1)
+    asm ("hlt");
+}
+
 static void register_int(uint8_t n, isr_t *isr, uint8_t dpl) {
   idt[n].addr_low = (uint32_t)isr & 0xffff;
   idt[n].addr_high = (uint32_t)isr >> 16;
@@ -142,6 +184,14 @@ void init_idt() {
 
   register_int(0x21, &kbd_isr, 0);
 
+  register_int(0x08, &udf_isr, 0);
+  register_int(0x08, &dfa_isr, 0);
+  register_int(0x0a, &tsf_isr, 0);
+  register_int(0x0b, &npf_isr, 0);
+  register_int(0x0c, &ssf_isr, 0);
+  register_int(0x0d, &gpf_isr, 0);
+  register_int(0x0e, &pff_isr, 0);
+
   outb(PIC_MCMD, PIC_RESET);
   outb(PIC_SCMD, PIC_RESET);
 
diff --git a/src/kernel/isrs.asm b/src/kernel/isrs.asm
index 9a9600c..4f2d4e2 100644
--- a/src/kernel/isrs.asm
+++ b/src/kernel/isrs.asm
@@ -6,6 +6,14 @@ global yield_isr
 global _start_user_mode
 global kbd_isr
 
+global udf_isr
+global dfa_isr
+global tsf_isr
+global npf_isr
+global ssf_isr
+global gpf_isr
+global pff_isr
+
 extern syscall_table
 extern active_task
 
@@ -13,14 +21,26 @@ extern delete_task
 extern advance_active_task
 extern on_kbd_isr
 extern make_sure_tasks
+extern exception_halt
 
 n_syscalls equ 0x9
 
+;section .bss
+;_debug_is_start_task resb 1
+;extern switch_to_kernel_cr3
+;extern switch_to_task_cr3
+
 section .text
 syscall_isr:
   cmp eax, n_syscalls
   jge .bad
 
+;  mov byte [_debug_is_start_task], 0
+;  cmp eax, 0x4
+;  jne .dont_set_debug
+;  mov byte [_debug_is_start_task], 1
+;.dont_set_debug:
+
   mov eax, dword [syscall_table + eax * 4]
 
   push edi
@@ -33,6 +53,16 @@ syscall_isr:
 
   add esp, 20
 
+;  cmp byte [_debug_is_start_task], 0
+;  je .dont_do_debug
+;  push eax
+;  call switch_to_kernel_cr3
+;  jmp $
+;  call switch_to_task_cr3
+;  pop eax
+;.dont_do_debug:
+
+._before_return:
   iret
 
 .bad:
@@ -86,12 +116,13 @@ yield_isr:
   mov edi, dword [eax + 24]
   mov ebp, dword [eax + 28]
 
-_before_start_task:
+._before_return:
   iret
 
 _start_user_mode:
   mov ax, 0x2b
   mov ds, ax
+  mov es, ax
 
   push dword 0x2b
   sub esp, 4
@@ -113,4 +144,42 @@ kbd_isr:
   pop edx
   pop ecx
   pop eax
-  iret
\ No newline at end of file
+  iret
+
+udf_isr:
+  push 0
+  push udid
+  call exception_halt
+
+dfa_isr:
+  push dfid
+  call exception_halt
+
+tsf_isr:
+  push tsid
+  call exception_halt
+
+npf_isr:
+  push npid
+  call exception_halt
+
+ssf_isr:
+  push ssid
+  call exception_halt
+
+gpf_isr:
+  push gpid
+  call exception_halt
+
+pff_isr:
+  push pfid
+  call exception_halt
+
+section .rodata
+udid db "UD", 0
+dfid db "DF", 0
+tsid db "TS", 0
+npid db "NP", 0
+ssid db "SS", 0
+gpid db "GP", 0
+pfid db "PF", 0
\ No newline at end of file
diff --git a/src/kernel/main.c b/src/kernel/main.c
index e2a23e8..06b83d1 100644
--- a/src/kernel/main.c
+++ b/src/kernel/main.c
@@ -136,7 +136,7 @@ void main() {
   logsz(nbuf);
   logsz("k\n\n");
 
-  if (!try_elf_run(drives, "BIN/INIT.ELF", ""))
+  if (!try_elf_run(drives, "bin/init", ""))
     PANIC("Failed to load init program.");
 
   init_kbd();
diff --git a/src/kernel/paging.c b/src/kernel/paging.c
index a0f7c3d..fbc33de 100644
--- a/src/kernel/paging.c
+++ b/src/kernel/paging.c
@@ -20,28 +20,16 @@ enum {
   PE_PRESENT  = 0x001
 };
 
-//TODO:
-//  try_elf_run needs to call these new functions.
-
-void *new_pd() {
-  uint32_t *pd = allocate_kernel_pages(1);
-  for (uint16_t i = 0; i < 1024; ++i)
-    pd[i] = 0;
-  return pd;
-}
-
-void free_pd(void *pd) {
-  uint32_t *pd_32 = pd;
-  for (uint16_t i = 0; i < 1024; ++i)
-    if (pd_32[i] & PE_PRESENT)
-      free_pages((void *)(pd_32[i] & PE_ADDR_MASK), 1);
-  free_pages(pd, 1);
-}
+#define KERNEL_END (0x08000000)
 
-void pd_map(void *pd, uint32_t physical_addr, uint32_t virtual_addr, bool writable) {
+static void pd_map(void *pd, uint32_t physical_addr, uint32_t virtual_addr, bool writable) {
   uint32_t *ptp = (uint32_t *)pd + (virtual_addr >> 22);
-  if (!(*ptp & PE_PRESENT))
-    *ptp = (uint32_t)allocate_kernel_pages(1) | PE_USER | PE_WRITABLE | PE_PRESENT;
+  if (!(*ptp & PE_PRESENT)) {
+    uint32_t *new_pt = allocate_kernel_pages(1);
+    for (uint16_t i = 0; i < 1024; ++i)
+      new_pt[i] = 0;
+    *ptp = (uint32_t)new_pt | PE_USER | PE_WRITABLE | PE_PRESENT;
+  }
   ((uint32_t *)(*ptp & PE_ADDR_MASK))[(virtual_addr >> 12) % 1024] = physical_addr | PE_USER | PE_PRESENT | (PE_WRITABLE * writable);
 }
 
@@ -51,26 +39,28 @@ static bool pd_is_mapped(void *pd, uint32_t vma) {
   return (pde & PE_PRESENT) && (((uint32_t *)(pde & PE_ADDR_MASK))[(vma >> 12) % 1024] & PE_PRESENT);
 }
 
-#define KERNEL_END (0x08000000)
-
 void free_task_pd(void *pd) {
   uint32_t *pd_32 = pd;
-  for (uint16_t i = 0; i < 1024; ++i)
+  for (uint16_t i = KERNEL_END / 4096 / 1024; i < 1024; ++i)
     if (pd_32[i] & PE_PRESENT) {
       uint32_t *pt_32 = (uint32_t *)(pd_32[i] & PE_ADDR_MASK);
-      if (i >= KERNEL_END >> 22)
-        for (uint16_t j = 0; j < 1024; ++j)
-          if (pt_32[j] & PE_PRESENT)
-            free_pages((void *)(pt_32[j] & PE_ADDR_MASK), 1);
+      for (uint16_t j = 0; j < 1024; ++j)
+        if (pt_32[j] & PE_PRESENT)
+          free_pages((void *)(pt_32[j] & PE_ADDR_MASK), 1);
       free_pages(pt_32, 1);
     }
   free_pages(pd, 1);
 }
 
+__attribute__ ((aligned (4096)))
+static uint32_t kmap[KERNEL_END / 4096];
+
 void *new_task_pd() {
-  uint32_t *pd = new_pd();
-  for (uint32_t addr = 0; addr < KERNEL_END; addr += 4096)
-    pd_map(pd, addr, addr, false);
+  uint32_t *pd = allocate_kernel_pages(1);
+  for (uint8_t i = 0; i < KERNEL_END / 4096 / 1024; ++i)
+    pd[i] = (uint32_t)(kmap + i * 1024) | PE_USER | PE_PRESENT;
+  for (uint16_t i = KERNEL_END / 4096 / 1024; i < 1024; ++i)
+    pd[i] = 0;
   return pd;
 }
 
@@ -129,6 +119,9 @@ void init_paging() {
   for (uint16_t i = 0; i < 1024; ++i)
     KPAGE_DIR[i] = (uint32_t)(KPAGE_TABLE_0 + i * 1024) | PE_WRITABLE | PE_PRESENT;
 
+  for (uint16_t i = 0; i < KERNEL_END / 4096; ++i)
+    kmap[i] = (i * 4096) | PE_USER | PE_PRESENT;
+
   asm volatile (
     "mov $0x00005000, %%eax\n"
     "mov %%eax, %%cr3\n"
diff --git a/src/kernel/paging.h b/src/kernel/paging.h
index 07bf386..6c1a6f5 100644
--- a/src/kernel/paging.h
+++ b/src/kernel/paging.h
@@ -3,10 +3,6 @@
 
 void init_paging();
 
-void *new_pd();
-void free_pd(void *pd);
-void pd_map(void *pd, uint32_t physical_addr, uint32_t virtual_addr, bool writable);
-
 void free_task_pd(void *pd);
 void *new_task_pd();
 void *pd_user_allocate(void *pd, uint32_t vma, uint32_t pages, bool writable);
diff --git a/src/kernel/pmap.c b/src/kernel/pmap.c
index 8634303..37c7261 100644
--- a/src/kernel/pmap.c
+++ b/src/kernel/pmap.c
@@ -77,8 +77,14 @@ void init_pagemap() {
 //a smarter algorithm might pick the smallest one available,
 //and go by bytes (or dwords) instead of bits where possible.
 void *allocate_kernel_pages(uint32_t n) {
+//logsz("trace: allocate_kernel_pages(");
+//char nbuf[11];
+//u32_dec(n, nbuf);
+//logsz(nbuf);
+//logsz(") = 0x");
+
   uint32_t run = 0;
-  
+
   for (uint32_t page = KBSS_START >> 12; page < USER_START >> 12; ++page) {
     if (PAGE_USED(page))
       run = 0;
@@ -87,6 +93,9 @@ void *allocate_kernel_pages(uint32_t n) {
       for (uint32_t i = start; i <= page; ++i)
         SET_PAGE(i);
       kernel_pages_left -= n;
+    //u32_hex(start << 12, nbuf);
+    //logsz(nbuf);
+    //logch('\n');
       return (void *)(start << 12);
     }
   }
@@ -98,8 +107,14 @@ void *allocate_kernel_pages(uint32_t n) {
 //a smarter algorithm might pick the smallest one available,
 //and go by bytes (or dwords) instead of bits where possible.
 void *allocate_user_pages(uint32_t n) {
+//logsz("trace: allocate_user_pages(");
+//char nbuf[11];
+//u32_dec(n, nbuf);
+//logsz(nbuf);
+//logsz(") = 0x");
+
   uint32_t run = 0;
-  
+
   for (uint32_t page = USER_START >> 12; page < 1048576; ++page) {
     if (PAGE_USED(page))
       run = 0;
@@ -108,6 +123,9 @@ void *allocate_user_pages(uint32_t n) {
       for (uint32_t i = start; i <= page; ++i)
         SET_PAGE(i);
       user_pages_left -= n;
+    //u32_hex(start << 12, nbuf);
+    //logsz(nbuf);
+    //logch('\n');
       return (void *)(start << 12);
     }
   }
@@ -117,6 +135,15 @@ void *allocate_user_pages(uint32_t n) {
 
 //in the future, change this to go by bytes or dwords instead of bits.
 void free_pages(const void *ptr, uint32_t n) {
+//logsz("trace: free_pages(0x");
+//char nbuf[11];
+//u32_hex(ptr, nbuf);
+//logsz(nbuf);
+//logsz(", ");
+//u32_dec(n, nbuf);
+//logsz(nbuf);
+//logsz(")\n");
+
   uint32_t page = (uint32_t)ptr >> 12;
   for (uint32_t i = page; i < page + n; ++i)
     CLEAR_PAGE(i);
diff --git a/src/kernel/task.c b/src/kernel/task.c
index e2c19ca..6c53510 100644
--- a/src/kernel/task.c
+++ b/src/kernel/task.c
@@ -91,6 +91,8 @@ void make_sure_tasks() {
 }
 
 void delete_task(struct task_state *state) {
+  switch_to_kernel_cr3();
   free_task_pd(state->page_directory);
+  switch_to_task_cr3();
   state->page_directory = 0;
 }
\ No newline at end of file
diff --git a/src/kernel/task.h b/src/kernel/task.h
index 838f27b..0fa9688 100644
--- a/src/kernel/task.h
+++ b/src/kernel/task.h
@@ -4,10 +4,11 @@
 #include <stdbool.h>
 #include <stdint.h>
 
+#define TASK_NAME_LEN 15
+
 struct task_state {
   uint32_t ret_addr;
   void *page_directory;
-  //maybe put scheduling or priviledge information here?
 
   uint32_t ebx;
   uint32_t ecx;
@@ -16,6 +17,8 @@ struct task_state {
   uint32_t edi;
   uint32_t ebp;
   uint32_t esp;
+
+  char name[TASK_NAME_LEN + 1];
 } __attribute__ ((packed));
 
 extern struct task_state *active_task;
diff --git a/src/kernel/vga.c b/src/kernel/vga.c
index c03e5f0..daa92fe 100644
--- a/src/kernel/vga.c
+++ b/src/kernel/vga.c
@@ -31,6 +31,8 @@ void vga_blank() {
 void vga_printch(char ch) {
   if (ch == '\n')
     cursor = ((cursor - VGA_START) / VGA_COLUMNS + 1) * VGA_COLUMNS + VGA_START;
+  else if (ch == '\b')
+    *--cursor = mask | ' ';
   else
     *cursor++ = mask | (uint8_t)ch;
   if (cursor == VGA_END)
diff --git a/src/user/dumphex/dumphex.c b/src/user/dumphex/dumphex.c
new file mode 100644
index 0000000..4c63a06
--- /dev/null
+++ b/src/user/dumphex/dumphex.c
@@ -0,0 +1,29 @@
+#include <knob/file.h>
+#include <knob/user.h>
+#include <knob/format.h>
+
+void main(const char *path) {
+  struct file *f = open_file(path);
+  if (!f) {
+    tell_user_sz("Couldn't open file.\n");
+    return;
+  }
+  char buf[] = { ' ', '\0', '\0', '\0' };
+  uint8_t v;
+  uint32_t a = 0;
+  while (read_from_file(f, 1, &v)) {
+    if (!(a & 0xf)) {
+      char buf2[] = {'0', 'x', '\0', '\0', '\0', '\0',
+                               '\0', '\0', '\0', '\0', '\0' };
+      itosz_h32(a, buf2 + 2);
+      tell_user_sz(buf2);
+      tell_user_sz(" |");
+    }
+    itosz_h8(v, buf + 1);
+    tell_user_sz(buf);
+    if (!(++a & 0xf))
+      tell_user_sz("\n");
+  }
+  tell_user_sz("\n");
+  close_file(f);
+}
\ No newline at end of file
diff --git a/src/user/dumptext/dumptext.c b/src/user/dumptext/dumptext.c
new file mode 100644
index 0000000..b10375c
--- /dev/null
+++ b/src/user/dumptext/dumptext.c
@@ -0,0 +1,15 @@
+#include <knob/file.h>
+#include <knob/user.h>
+
+void main(const char *path) {
+  struct file *f = open_file(path);
+  if (!f) {
+    tell_user_sz("Couldn't open file.\n");
+    return;
+  }
+  char buf[] = { '\0', '\0' };
+  while (read_from_file(f, 1, buf))
+    tell_user_sz(buf);
+  tell_user_sz("\n");
+  close_file(f);
+}
\ No newline at end of file
diff --git a/src/user/hello/hello.asm b/src/user/hello/hello.asm
new file mode 100644
index 0000000..65d32be
--- /dev/null
+++ b/src/user/hello/hello.asm
@@ -0,0 +1,14 @@
+bits 32
+
+global _entry
+
+section .text
+_entry:
+  mov eax, 0x5
+  mov ebx, hello
+  int 0x30
+
+  int 0x38
+
+section .data
+hello db "Hello, world!", 0x0a, 0
\ No newline at end of file
diff --git a/src/user/highway/highway.c b/src/user/highway/highway.c
index effc131..8dc0080 100644
--- a/src/user/highway/highway.c
+++ b/src/user/highway/highway.c
@@ -6,8 +6,13 @@
 //TODO: have an active disk and/or directory
 
 void main() {
-  char path_buf[1024 + 4] = "BIN/";
+  char path_buf[1024 + 4] = "bin/";
   char *const line_buf = path_buf + 4;
+
+  tell_user_sz("Highway, Portland Command Shell, started.\n"
+               "Type \"exit\" to quit.\n");
+  yield_task();
+
   while (1) {
     tell_user_sz("> ");
     ask_user_line_sz(line_buf, 1023);
diff --git a/src/user/include/knob/format.h b/src/user/include/knob/format.h
index 6c4aa5d..89402c0 100644
--- a/src/user/include/knob/format.h
+++ b/src/user/include/knob/format.h
@@ -6,5 +6,7 @@
 
 bool try_sntoi(const char *s, uint32_t n, uint32_t *out);
 void itosz(uint32_t i, char *out);
+void itosz_h8(uint8_t i, char *out);
+void itosz_h32(uint32_t i, char *out);
 
 #endif
\ No newline at end of file
diff --git a/src/user/init/init.c b/src/user/init/init.c
index 64c534e..390b731 100644
--- a/src/user/init/init.c
+++ b/src/user/init/init.c
@@ -3,25 +3,28 @@
 #include <knob/task.h>
 
 void start(const char *cmd) {
+  tell_user_sz("[init] Starting ");
   tell_user_sz(cmd);
   tell_user_sz(": ");
   tell_user_sz(
     try_run_command(cmd)
-      ? "success\n"
-      : "failed\n"
+      ? "Succeded.\n"
+      : "Failed.\n"
   );
+  tell_user_sz("[init] Yielding.\n");
+  yield_task();
 }
 
-#define STARTUP_FILE_PATH "SYS/STARTUP.RC"
+#define STARTUP_FILE_PATH "sys/startup.rc"
 
 void main() {
   struct file *f = open_file(STARTUP_FILE_PATH);
   if (!f) {
-    tell_user_sz("Could not open " STARTUP_FILE_PATH "\n");
+    tell_user_sz("Could not open " STARTUP_FILE_PATH ".\n");
     return;
   }
 
-  tell_user_sz("[init] Reading from " STARTUP_FILE_PATH ":\n");
+  tell_user_sz("[init] Reading from " STARTUP_FILE_PATH ".\n");
 
   char buf[1024];
   char *bufp = buf;
@@ -43,5 +46,5 @@ void main() {
 
   close_file(f);
 
-  tell_user_sz("[init] Done.\n");
+  tell_user_sz("[init] Done starting programs.\n");
 }
diff --git a/src/user/knob/entry.asm b/src/user/knob/entry.asm
index 18faf7f..acf6f5f 100644
--- a/src/user/knob/entry.asm
+++ b/src/user/knob/entry.asm
@@ -12,7 +12,6 @@ _entry:
   mov esp, stack
   push edx
 
-  ;TODO: heap stuff?
   ;TODO: determine current_disk
   ;any further needed initialization
 
diff --git a/src/user/knob/format.c b/src/user/knob/format.c
index 087f6fd..645fb73 100644
--- a/src/user/knob/format.c
+++ b/src/user/knob/format.c
@@ -28,4 +28,18 @@ void itosz(uint32_t i, char *out) {
     }
   }
   *out = '\0';
+}
+
+const char *const hex_digits = "0123456789abcdef";
+
+void itosz_h8(uint8_t i, char *out) {
+  out[0] = hex_digits[i >> 4];
+  out[1] = hex_digits[i & 0xf];
+  out[2] = '\0';
+}
+
+void itosz_h32(uint32_t i, char *out) {
+  for (uint8_t digit = 0; digit < 8; ++digit)
+    out[digit] = hex_digits[(i >> (28 - digit * 4)) & 0xf];
+  out[8] = '\0';
 }
\ No newline at end of file
diff --git a/src/user/knob/user.c b/src/user/knob/user.c
index 4ef3321..c84977c 100644
--- a/src/user/knob/user.c
+++ b/src/user/knob/user.c
@@ -165,16 +165,20 @@ uint32_t ask_user_line_sz(char *sz, uint32_t max_length) {
       goto replace;
     if (key & 0x80)
       goto replace;//TODO
+    if (key == '\b') {
+      if (i) {
+        --i;
+        _log_string("\b");
+      }
+      goto replace;
+    }
 
     log_buf[0] = key;
     _log_string(log_buf);
 
-    if (key == '\b')
-      i -= i ? 2 : 1;
-    else if (key == '\n')
+    if (key == '\n')
       break;
-    else
-      sz[i] = key;
+    sz[i] = key;
   }
 
   sz[i] = '\0';
-- 
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