preliminary works to use the gs register in user space

hermit/arch/x86/include/asm/tasks.h

@@ -55,11 +55,12 @@ void switch_context(size_t** stack);
  * @param task Pointer to the task structure
  * @param ep The entry point for code execution
  * @param arg Arguments list pointer for the task's stack
+ * @param core_id Id of the core, which is firstly used by the task 
  * @return
  * - 0 on success
  * - -EINVAL (-22) on failure
  */
-int create_default_frame(task_t* task, entry_point_t ep, void* arg);
+int create_default_frame(task_t* task, entry_point_t ep, void* arg, uint32_t core_id);
 
 /** @brief Jump to user code
  *

hermit/arch/x86/kernel/entry.asm

@@ -38,6 +38,7 @@ extern kernel_end
 
 MSR_FS_BASE equ 0xc0000100
 MSR_GS_BASE equ 0xc0000101
+MSR_KERNEL_GS_BASE equ 0xc0000102
 
 ; We use a special name to map this section at the begin of our kernel
 ; =>  Multiboot expects its magic number at the beginning of the kernel.
@@ -350,8 +351,10 @@ align 16
 isrsyscall:
     ; IF flag is already cleared
     ; cli
+
     ; only called from user space => get kernel-level selector
     swapgs
+
     ; get kernel stack
     xchg rsp, [gs:kernel_stack]
 
@@ -391,8 +394,10 @@ isrsyscall:
 
     cli
 
-    ; restore registers
+    ; restore return value
     pop rax
+
+    ; restore registers
     pop rsi
     pop rdi
     pop rcx
@@ -407,6 +412,7 @@ isrsyscall:
 
     ; set user-level selector
     swapgs
+
     ; EFLAGS (and IF flag) will be restored by sysret
     ; sti
     o64 sysret
@@ -536,12 +542,16 @@ common_switch:
     call finish_task_switch
 
 no_context_switch:
+    ; do we interrupt user-level code?
+    cmp QWORD [rsp+24+18*8], 0x08
+    je short kernel_space2
+    swapgs  ; set GS to the user-level selector
+kernel_space2:
     ; restore fs / gs register
 global Lpatch2
 Lpatch2:
     jmp short Lwrfsgs    ; we patch later this jump to enable wrfsbase/wrgsbase
-    add rsp, 8
-    ;pop r15
+    pop r15
     ;wrgsbase r15        ; currently, we don't use the gs register
     pop r15
     wrfsbase r15
@@ -575,11 +585,6 @@ Lgo3:
     pop rcx
     pop rax
 
-    ; do we interrupt user-level code?
-    cmp QWORD [rsp+24], 0x08
-    je short kernel_space2
-    swapgs  ; set GS to the user-level selector
-kernel_space2:
     add rsp, 16
     iretq
 

hermit/arch/x86/kernel/processor.c

@@ -33,9 +33,9 @@
 #include <hermit/tasks.h>
 
 /*
- *  * Note that linker symbols are not variables, they have no memory allocated for
- *   * maintaining a value, rather their address is their value.
- *    */
+ * Note that linker symbols are not variables, they have no memory allocated for
+ * maintaining a value, rather their address is their value.
+ */
 extern const void percore_start;
 extern const void percore_end0;
 extern const void percore_end;

hermit/arch/x86/kernel/tasks.c

@@ -40,6 +40,13 @@
 
 #define START_ADDRESS	0x40200000
 
+/*
+ * Note that linker symbols are not variables, they have no memory allocated for
+ * maintaining a value, rather their address is their value.
+ */
+extern const void percore_start;
+extern const void percore_end0;
+
 extern uint64_t base;
 
 static inline void enter_user_task(size_t ep, size_t stack)
@@ -128,7 +135,7 @@ size_t* get_current_stack(void)
 	return curr_task->last_stack_pointer;
 }
 
-int create_default_frame(task_t* task, entry_point_t ep, void* arg)
+int create_default_frame(task_t* task, entry_point_t ep, void* arg, uint32_t core_id)
 {
 	size_t *stack;
 	struct state *stptr;
@@ -179,6 +186,7 @@ int create_default_frame(task_t* task, entry_point_t ep, void* arg)
 	}
 	stptr->cs = 0x08;
 	stptr->ss = 0x10;
+	stptr->gs = core_id * ((size_t) &percore_end0 - (size_t) &percore_start); 
 	stptr->rflags = 0x1202;
 	stptr->userrsp = stptr->rsp;
 

hermit/kernel/tasks.c

@@ -325,7 +325,7 @@ int clone_task(tid_t* id, entry_point_t ep, void* arg, uint8_t prio)
 			if (id)
 				*id = i;
 
-			ret = create_default_frame(task_table+i, ep, arg);
+			ret = create_default_frame(task_table+i, ep, arg, core_id);
 			if (ret)
 				goto out;
 
@@ -418,7 +418,7 @@ int create_task(tid_t* id, entry_point_t ep, void* arg, uint8_t prio, uint32_t c
 				*id = i;
 			//kprintf("Create task %d with pml4 at 0x%llx\n", i, task_table[i].page_map);
 
-			ret = create_default_frame(task_table+i, ep, arg);
+			ret = create_default_frame(task_table+i, ep, arg, core_id);
 			if (ret)
 				goto out;