feat: smart: user space context optimization

This patch optimizes the user-space context handling in the ARM64
architecture, specifically improving how the context is saved and
restored during system calls and interrupts. The changes make the
code more efficient and easier to maintain, while ensuring proper
preservation of user context during system transitions.

Changes:
- Introduced a parameter for context saving to improve flexibility.
- Replaced hardcoded stack pointer operations with frame-relative
  references for better readability and code reuse.
- Simplified context restoration, removing redundant operations like
  loading/storing floating-point registers.

Signed-off-by: Shell <[email protected]>

components/lwp/arch/aarch64/cortex-a/lwp_gcc.S

@@ -17,6 +17,7 @@
 #include <rtconfig.h>
 #include <asm-generic.h>
 #include <asm-fpu.h>
+#include <vector_gcc.h>
 #include <armv8.h>
 #include <lwp_arch.h>
 
@@ -105,6 +106,7 @@ arch_get_user_sp:
 .global arch_clone_exit
 arch_fork_exit:
 arch_clone_exit:
+    mov x0, xzr
     b  arch_syscall_exit
 
 /*
@@ -131,12 +133,31 @@ START_POINT(SVC_Handler)
     /* x0 is initial sp */
     mov sp, x0
 
+    bl _SVC_Handler
+
+    /* jump explictly, make this code position independant */
+    b arch_syscall_exit
+START_POINT_END(SVC_Handler)
+
+TRACE_SYMBOL(_SVC_Handler)
+#define FRAME_REG x19
+
+/**
+ * x0 -> frame_addr
+ */
+_SVC_Handler:
+    .local _SVC_Handler
+
+    stp fp, lr, [sp, -16]!
+    mov fp, sp
+
+    mov FRAME_REG, x0   /* save the value of frame address */
     msr daifclr, #3  /* enable interrupt */
 
     GET_THREAD_SELF x0
     bl  lwp_user_setting_save
 
-    ldp x8, x9, [sp, #(CONTEXT_OFFSET_X8)]
+    ldp x8, x9, [FRAME_REG, #(CONTEXT_OFFSET_X8)]
     and x0, x8, #0xf000
     cmp x0, #0xe000
     beq arch_signal_quit
@@ -149,78 +170,46 @@ START_POINT(SVC_Handler)
     cmp x0, xzr
     mov x30, x0
     beq arch_syscall_exit
-    ldp x0, x1, [sp, #(CONTEXT_OFFSET_X0)]
-    ldp x2, x3, [sp, #(CONTEXT_OFFSET_X2)]
-    ldp x4, x5, [sp, #(CONTEXT_OFFSET_X4)]
-    ldp x6, x7, [sp, #(CONTEXT_OFFSET_X6)]
+    ldp x0, x1, [FRAME_REG, #(CONTEXT_OFFSET_X0)]
+    ldp x2, x3, [FRAME_REG, #(CONTEXT_OFFSET_X2)]
+    ldp x4, x5, [FRAME_REG, #(CONTEXT_OFFSET_X4)]
+    ldp x6, x7, [FRAME_REG, #(CONTEXT_OFFSET_X6)]
     blr x30
-    /* jump explictly, make this code position independant */
-    b arch_syscall_exit
-START_POINT_END(SVC_Handler)
 
-.global arch_syscall_exit
+    ldp fp, lr, [sp], 16
+    ret
+
+/**
+ * void arch_syscall_exit(long rc)
+ */
 arch_syscall_exit:
+    .global arch_syscall_exit
 
     /**
-     * @brief back up former x0 which is required to restart syscall, then setup
+     * backup former x0 which is required to restart syscall, then setup
      * syscall return value in stack frame
      */
     mov x1, sp
     bl arch_syscall_prepare_signal
 
+    /**
+     * disable local irq so we don't messup with the spsr_el1 witch is not saved
+     * for kernel space IRQ/EXCEPTION
+     */
     msr daifset, #3
 
-    ldp x2, x3, [sp], #0x10  /* SPSR and ELR. */
-    msr spsr_el1, x3
-    msr elr_el1, x2
-
-    ldp x29, x30, [sp], #0x10
-    msr sp_el0, x29
-    ldp x28, x29, [sp], #0x10
-    msr fpcr, x28
-    msr fpsr, x29
-    ldp x28, x29, [sp], #0x10
-    ldp x26, x27, [sp], #0x10
-    ldp x24, x25, [sp], #0x10
-    ldp x22, x23, [sp], #0x10
-    ldp x20, x21, [sp], #0x10
-    ldp x18, x19, [sp], #0x10
-    ldp x16, x17, [sp], #0x10
-    ldp x14, x15, [sp], #0x10
-    ldp x12, x13, [sp], #0x10
-    ldp x10, x11, [sp], #0x10
-    ldp x8, x9, [sp], #0x10
-    ldp x6, x7, [sp], #0x10
-    ldp x4, x5, [sp], #0x10
-    ldp x2, x3, [sp], #0x10
-    ldp x0, x1, [sp], #0x10
-    RESTORE_FPU sp
+    b arch_ret_to_user
 
 /* the sp is reset to the outer most level, irq and fiq are disabled */
 START_POINT(arch_ret_to_user)
     msr daifset, #3
-    /* save exception frame */
-    SAVE_FPU sp
-    stp x0, x1, [sp, #-0x10]!
-    stp x2, x3, [sp, #-0x10]!
-    stp x4, x5, [sp, #-0x10]!
-    stp x6, x7, [sp, #-0x10]!
-    stp x8, x9, [sp, #-0x10]!
-    stp x10, x11, [sp, #-0x10]!
-    stp x12, x13, [sp, #-0x10]!
-    stp x14, x15, [sp, #-0x10]!
-    stp x16, x17, [sp, #-0x10]!
-    stp x18, x19, [sp, #-0x10]!
-    stp x20, x21, [sp, #-0x10]!
-    stp x22, x23, [sp, #-0x10]!
-    stp x24, x25, [sp, #-0x10]!
-    stp x26, x27, [sp, #-0x10]!
-    stp x28, x29, [sp, #-0x10]!
-
-    mrs x0, fpcr
-    mrs x1, fpsr
-    stp x0, x1, [sp, #-0x10]!
-    stp x29, x30, [sp, #-0x10]!
+
+    ldr x2, [sp, #CONTEXT_OFFSET_SP_EL0]
+    msr sp_el0, x2
+    ldr x2, [sp, #CONTEXT_OFFSET_ELR_EL1]
+    msr elr_el1, x2
+    ldr x3, [sp, #CONTEXT_OFFSET_SPSR_EL1]
+    msr spsr_el1, x3
 
     /* pre-action */
     bl lwp_check_debug
@@ -231,7 +220,8 @@ START_POINT(arch_ret_to_user)
     msr daifclr, #3
     mov x0, xzr
     b sys_exit
-1:
+
+1:  /* handling dbg */
     /* check if dbg ops exist */
     ldr x0, =rt_dbg_ops
     ldr x0, [x0]
@@ -243,104 +233,42 @@ START_POINT(arch_ret_to_user)
     orr x2, x2, x1
     msr spsr_el1, x2
     b 3f
-2:
+2:  /* clear software step */
     bic x2, x2, x1
     msr spsr_el1, x2
-3:
+3:  /* handling signal */
 
     /**
-     * push 2 dummy words to simulate a exception frame of interrupt
-     * Note: in kernel state, the context switch dont saved the context
+     * push updated spsr & elr to exception frame.
+     * Note: these 2 maybe updated after handling dbg
      */
     mrs x0, spsr_el1
+    str x0, [sp, #CONTEXT_OFFSET_SPSR_EL1]
     mrs x1, elr_el1
-    stp x1, x0, [sp, #-0x10]!
+    str x1, [sp, #CONTEXT_OFFSET_ELR_EL1]
     mov x0, sp
+
+    /* restore the thread execution environment */
     msr daifclr, #3
     bl lwp_thread_signal_catch
+
+    /* restore the exception-return exec-flow */
     msr daifset, #3
-    ldp x1, x0, [sp], #0x10
-    msr spsr_el1, x0
-    msr elr_el1, x1
 
     /* check debug */
-    /* restore exception frame */
-    ldp x29, x30, [sp], #0x10
-    ldp x0, x1, [sp], #0x10
-    msr fpcr, x0
-    msr fpsr, x1
-
-    ldp x28, x29, [sp], #0x10
-    ldp x26, x27, [sp], #0x10
-    ldp x24, x25, [sp], #0x10
-    ldp x22, x23, [sp], #0x10
-    ldp x20, x21, [sp], #0x10
-    ldp x18, x19, [sp], #0x10
-    ldp x16, x17, [sp], #0x10
-    ldp x14, x15, [sp], #0x10
-    ldp x12, x13, [sp], #0x10
-    ldp x10, x11, [sp], #0x10
-    ldp x8, x9, [sp], #0x10
-    ldp x6, x7, [sp], #0x10
-    ldp x4, x5, [sp], #0x10
-    ldp x2, x3, [sp], #0x10
-    ldp x0, x1, [sp], #0x10
-    RESTORE_FPU sp
 
-    stp x0, x1, [sp, #-0x10]!
     ldr x0, =rt_dbg_ops
     ldr x0, [x0]
     cmp x0, xzr
-    ldp x0, x1, [sp], #0x10
-    beq 1f
 
-    /* save */
-    SAVE_FPU sp
-    stp x0, x1, [sp, #-0x10]!
-    stp x2, x3, [sp, #-0x10]!
-    stp x4, x5, [sp, #-0x10]!
-    stp x6, x7, [sp, #-0x10]!
-    stp x8, x9, [sp, #-0x10]!
-    stp x10, x11, [sp, #-0x10]!
-    stp x12, x13, [sp, #-0x10]!
-    stp x14, x15, [sp, #-0x10]!
-    stp x16, x17, [sp, #-0x10]!
-    stp x18, x19, [sp, #-0x10]!
-    stp x20, x21, [sp, #-0x10]!
-    stp x22, x23, [sp, #-0x10]!
-    stp x24, x25, [sp, #-0x10]!
-    stp x26, x27, [sp, #-0x10]!
-    stp x28, x29, [sp, #-0x10]!
-    mrs x0, fpcr
-    mrs x1, fpsr
-    stp x0, x1, [sp, #-0x10]!
-    stp x29, x30, [sp, #-0x10]!
+    beq 1f
 
-    mrs x0, elr_el1
+    ldr x0, [sp, #CONTEXT_OFFSET_ELR_EL1]
     bl dbg_attach_req
 
-    /* restore */
-    ldp x29, x30, [sp], #0x10
-    ldp x0, x1, [sp], #0x10
-    msr fpcr, x0
-    msr fpsr, x1
-    ldp x28, x29, [sp], #0x10
-    ldp x26, x27, [sp], #0x10
-    ldp x24, x25, [sp], #0x10
-    ldp x22, x23, [sp], #0x10
-    ldp x20, x21, [sp], #0x10
-    ldp x18, x19, [sp], #0x10
-    ldp x16, x17, [sp], #0x10
-    ldp x14, x15, [sp], #0x10
-    ldp x12, x13, [sp], #0x10
-    ldp x10, x11, [sp], #0x10
-    ldp x8, x9, [sp], #0x10
-    ldp x6, x7, [sp], #0x10
-    ldp x4, x5, [sp], #0x10
-    ldp x2, x3, [sp], #0x10
-    ldp x0, x1, [sp], #0x10
-    RESTORE_FPU sp
 1:
+    RESTORE_IRQ_CONTEXT_NO_SPEL0
+
     eret
 START_POINT_END(arch_ret_to_user)
 
@@ -410,41 +338,16 @@ arch_syscall_restart:
     /* restore previous exception frame */
     msr spsel, #0
 
-    ldp x2, x3, [sp], #0x10
-    msr elr_el1, x2
-    msr spsr_el1, x3
-
-    ldp x29, x30, [sp], #0x10
-
-    ldp x28, x29, [sp], #0x10
-    msr fpcr, x28
-    msr fpsr, x29
-
-    ldp x28, x29, [sp], #0x10
-    ldp x26, x27, [sp], #0x10
-    ldp x24, x25, [sp], #0x10
-    ldp x22, x23, [sp], #0x10
-    ldp x20, x21, [sp], #0x10
-    ldp x18, x19, [sp], #0x10
-    ldp x16, x17, [sp], #0x10
-    ldp x14, x15, [sp], #0x10
-    ldp x12, x13, [sp], #0x10
-    ldp x10, x11, [sp], #0x10
-    ldp x8, x9, [sp], #0x10
-    ldp x6, x7, [sp], #0x10
-    ldp x4, x5, [sp], #0x10
-    ldp x2, x3, [sp], #0x10
-    ldp x0, x1, [sp], #0x10
-    RESTORE_FPU sp
+    RESTORE_IRQ_CONTEXT_NO_SPEL0
 
     msr spsel, #1
 
     b vector_exception
 
 arch_signal_quit:
 
-    /* drop current exception frame */
-    add sp, sp, #CONTEXT_SIZE
+    /* drop current exception frame & sigreturn */
+    add sp, sp, #(CONTEXT_SIZE + 0x10)
     mov x1, sp
     mrs x0, sp_el0
     bl  arch_signal_ucontext_restore
@@ -460,35 +363,12 @@ arch_signal_quit:
     /* restore previous exception frame */
     msr spsel, #0
 
-    ldp x2, x3, [sp], #0x10
-    msr elr_el1, x2
-    msr spsr_el1, x3
-
-    ldp x29, x30, [sp], #0x10
-
-    ldp x28, x29, [sp], #0x10
-    msr fpcr, x28
-    msr fpsr, x29
-
-    ldp x28, x29, [sp], #0x10
-    ldp x26, x27, [sp], #0x10
-    ldp x24, x25, [sp], #0x10
-    ldp x22, x23, [sp], #0x10
-    ldp x20, x21, [sp], #0x10
-    ldp x18, x19, [sp], #0x10
-    ldp x16, x17, [sp], #0x10
-    ldp x14, x15, [sp], #0x10
-    ldp x12, x13, [sp], #0x10
-    ldp x10, x11, [sp], #0x10
-    ldp x8, x9, [sp], #0x10
-    ldp x6, x7, [sp], #0x10
-    ldp x4, x5, [sp], #0x10
-    ldp x2, x3, [sp], #0x10
-    ldp x0, x1, [sp], #0x10
-    RESTORE_FPU sp
+    RESTORE_IRQ_CONTEXT_NO_SPEL0
 
     msr spsel, #1
 
+    SAVE_IRQ_CONTEXT
+
     b arch_ret_to_user
 
 /**