give each thread a syscall stack instead of the silliness from before

src/kernel/process.asm

@@ -18,6 +18,11 @@
 bits 64
 default rel
 
+section .bss
+
+  resb 16384
+temporary_stack:
+
 section .text
 
 ;referenced in process.c
@@ -42,3 +47,9 @@ thread_start:
   xor r15, r15
 
   o64 sysret
+
+;referenced in process.c
+global with_temporary_stack
+with_temporary_stack:
+  mov rsp, temporary_stack
+  jmp rdi

src/kernel/process.c

@@ -18,7 +18,6 @@
 #include "framebuffer.h"
 #include "ipc-dgram.h"
 #include "scheduler.h"
-#include "syscalls.h"
 #include "process.h"
 #include "utility.h"
 #include "paging.h"
@@ -446,6 +445,8 @@ int syscall_start_elf(const char *path, const struct process_start_info *info) {
 
 void destroy_process(struct process *process) {
 
+  assert(process->n_threads == 0)
+
   if (process->files) {
     for (int i = 0; i < process->files_buffer_size; ++i)
       if (process->files[i].fs != 0)
@@ -499,23 +500,23 @@ void destroy_thread(struct thread *thread) {
 
   assert(thread->process->n_threads >= 1)
 
-  if (thread->process->n_threads == 1)
+  --thread->process->n_threads;
+
+  for (void *p = thread->syscall_stack_bottom; p < thread->syscall_stack_top; p += 4096)
+    unmap_and_free_kernel_page(p);
+
+  if (thread->process->n_threads == 0)
     destroy_process(thread->process);
-
-  else {
-
-    --thread->process->n_threads;
-
+  else
     for (void *p = thread->stack_bottom; p < thread->stack_top; p += 4096)
       unmap_page_for_process(thread->process, p);
 
-  }
-
   heap_dealloc(thread, sizeof(struct thread));
 
 }
 
 #define INITIAL_STACK_SIZE (16 << 20)
+#define INITIAL_SYSCALL_STACK_SIZE 16384
 
 void create_thread(struct process *process, struct thread *thread_out) {
 
@@ -539,9 +540,19 @@ void create_thread(struct process *process, struct thread *thread_out) {
 
   }
 
+  void *syscall_stack_bottom = find_free_kernel_region(INITIAL_SYSCALL_STACK_SIZE);
+
+  for (int i = 0; i < INITIAL_SYSCALL_STACK_SIZE / 4096; ++i) {
+    uint64_t pma = take_free_physical_page();
+    map_in_kernel_page_table(
+      pma, syscall_stack_bottom + i * 4096, 1, 0);
+  }
+
   thread_out->process = process;
   thread_out->stack_bottom = stack_bottom_vma;
   thread_out->stack_top = stack_bottom_vma + INITIAL_STACK_SIZE;
+  thread_out->syscall_stack_bottom = syscall_stack_bottom;
+  thread_out->syscall_stack_top = syscall_stack_bottom + INITIAL_SYSCALL_STACK_SIZE;
 
   ++process->n_threads;
 
@@ -553,15 +564,23 @@ void create_thread(struct process *process, struct thread *thread_out) {
 
 struct thread *running_thread = 0;
 
+//defined in process.asm.
+//function should not return.
+[[noreturn]] void with_temporary_stack(void (*function)());
+
 [[noreturn]] static void syscall_end_thread_with_temporary_stack() {
-  destroy_syscall_stack(most_recent_syscall_stack);
+
+  assert(running_thread != 0)
+
+  struct thread *the_thread = running_thread;
+  running_thread = 0;
+
+  destroy_thread(the_thread);
   resume_next_continuation();
+
 }
 
 [[noreturn]] void syscall_end_thread() {
-  assert(running_thread != 0)
-  destroy_thread(running_thread);
-  running_thread = 0;
   with_temporary_stack(&syscall_end_thread_with_temporary_stack);
 }
 

src/kernel/process.h

@@ -83,6 +83,7 @@ struct process {
 //return value might be invalidated by future allocation of file handles for this process.
 struct process_file_info *get_file_info(struct process *process, file_handle_t handle);
 
+//layout used in syscalls.asm
 struct thread {
 
   struct process *process;
@@ -91,6 +92,10 @@ struct thread {
   void *stack_bottom;
   void *stack_top;
 
+  //both page-aligned
+  void *syscall_stack_bottom;
+  void *syscall_stack_top;
+
 };
 
 extern struct thread *running_thread;
@@ -105,6 +110,7 @@ void map_page_for_process(
   void *virtual_base, int writable, int executable, int owned);
 
 //virtual base must be page-aligned, in bottom p3, and not zero.
+//also frees physical page if owned by process.
 void unmap_page_for_process(
   struct process *process, void *virtual_base);
 
@@ -127,6 +133,7 @@ struct process *start_elf(const char *uri);
 int syscall_start_elf(const char *path, const struct process_start_info *info);
 
 void destroy_process(struct process *process);
+//must not be called with syscall stack of the thread being destroyed
 void destroy_thread(struct thread *thread);
 
 [[noreturn]] void syscall_illegal_args();

src/kernel/syscalls.asm

@@ -18,133 +18,42 @@
 bits 64
 default rel
 
-extern destroy_syscall_stack
-extern create_syscall_stack
+;defined in syscalls.c
 extern syscall_entry_c
 
-section .bss
-
-  resb 1 << 15
-temp_syscall_stack:
-
-available_syscall_stack_count equ 128
-available_syscall_stacks:
-  resq available_syscall_stack_count
-
-global most_recent_syscall_stack
-most_recent_syscall_stack:
-  resq 1
+extern running_thread
 
 section .text
 
 ;system call number is in rax.
 ;system call arguments are in rdi, rsi, rdx.
 ;system call returns a value in rax.
+;depends on layout of struct thread from process.h
 syscall_entry:
+  mov r8, qword [running_thread]
+  test r8, r8
+  jz .assert_fail
 
-  xor r8, r8
-.find_stack_loop:
-
-  mov r9, qword [available_syscall_stacks + r8 * 8]
-  test r9, r9
-  jnz .got_syscall_stack
-
-  inc r8
-  cmp r8, available_syscall_stack_count
-  jne .find_stack_loop
-
-  mov qword [temp_syscall_stack - 8], rsp
-  mov rsp, temp_syscall_stack - 8
-  push r11
-  push rcx
-  push rax
-  push rdi
-  push rsi
-  push rdx
-
-  call create_syscall_stack
-  mov r9, rax
-
-  pop rdx
-  pop rsi
-  pop rdi
-  pop rax
-  pop rcx
-  pop r11
-  pop rsp
-
-  jmp .common
-
-.got_syscall_stack:
-  mov qword [available_syscall_stacks + r8 * 8], 0
-
-.common:
-  mov qword [r9 - 8], rsp
-  mov rsp, r9
-  mov qword [most_recent_syscall_stack], rsp
+  mov r8, qword [r8 + 32]
+  mov qword [r8 - 8], rsp
+  mov rsp, r8
   sub rsp, 8
-  push r11
   push rcx
+  push r11
 
   mov rcx, rax
   call syscall_entry_c
 
-  pop rcx
-  pop r11
-
-  xor r8, r8
-.find_place_to_put_stack:
-
-  mov r9, qword [available_syscall_stacks + r8 * 8]
-  test r9, r9
-  jz .got_place
-
-  inc r8
-  cmp r8, available_syscall_stack_count
-  jne .find_stack_loop
-
-  mov rdi, rsp
-  add rdi, 8
-
-  pop rsp
-
-  mov qword [temp_syscall_stack - 8], rsp
-  mov rsp, temp_syscall_stack - 8
-  push rax
-  push rcx
-  push r11
-
-  call destroy_syscall_stack
-
   pop r11
   pop rcx
-  pop rax
-  jmp .common_2
-
-.got_place:
-  mov r9, rsp
-  add r9, 8
-  mov qword [available_syscall_stacks + r8 * 8], r9
-
-.common_2:
   pop rsp
   o64 sysret
 
+.assert_fail:
+  ud2
+
 global init_syscalls
 init_syscalls:
-  sub rsp, 8
-  mov qword [rsp], 0
-
-.create_stack_loop:
-  call create_syscall_stack
-  mov rdi, qword [rsp]
-  mov qword [available_syscall_stacks + rdi * 8], rax
-  inc qword [rsp]
-  cmp rdi, available_syscall_stack_count - 1
-  jne .create_stack_loop
-
-  add rsp, 8
-
   mov ecx, 0xc0000080
   rdmsr
   or al, 0x01
@@ -167,8 +76,3 @@ init_syscalls:
   wrmsr
 
   ret
-
-global with_temporary_stack
-with_temporary_stack:
-  mov rsp, temp_syscall_stack
-  jmp rdi

src/kernel/syscalls.h

@@ -25,12 +25,3 @@ void init_syscalls();
 void register_syscall(
   int number,
   uint64_t (*handler)(uint64_t arg1, uint64_t arg2, uint64_t arg3));
-
-//the top of the syscall stack of the most recently started syscall.
-//kind of a hack, used in the end_thread syscall to deallocate that stack
-//and in the fork_thread syscall to copy the stack.
-extern void *most_recent_syscall_stack;
-
-//also kind of a hack. switches to temporary stack and runs f with that stack.
-//f should not return. this does not touch most_recent_syscall_stack.
-[[noreturn]] void with_temporary_stack(void (*f)());