debug(kernel): #PF 打印 rbp 链回溯（崩溃帧 + 4 级返回地址）

devfs_directory.find 崩溃（cr2=0x0 写 NULL，rax=rsp=0x6f0 异常）说明调用链栈已被破坏。isr.s 新增 _fault_rbp 保存异常现场 rbp，idt.vp [PF] 分支打印 [STK] 链定位栈损坏源。

VKernel/Kernel/intr/idt.vp

@@ -124,6 +124,31 @@ def isrCommonhandler(interrupt: t.CInt):
         buf: t.CArray[t.CChar, 100]
         viperlib.snprintf(c.Addr(buf), 100, "[PF] cr2=0x%lx rip=0x%lx err=0x%lx rsp=0x%lx\n", cr2, fault_rip, fault_err, fault_rsp)
         serial.puts(buf)
+        # [STK] rbp 链回溯（定位栈损坏源：崩溃帧 + 4 级调用链的返回地址）
+        fr0: t.CUInt64T = 0
+        fr1: t.CUInt64T = 0
+        fr2: t.CUInt64T = 0
+        fr3: t.CUInt64T = 0
+        fr4: t.CUInt64T = 0
+        c.Asm(f"""mov rax, [_fault_rbp]
+                mov {c.AsmOut(fr0, t.ASM_DESCR.OUTPUT_REG)}, rax
+                mov rax, [rax + 8]
+                mov {c.AsmOut(fr1, t.ASM_DESCR.OUTPUT_REG)}, rax
+                mov rax, [_fault_rbp]
+                mov rax, [rax]
+                mov {c.AsmOut(fr2, t.ASM_DESCR.OUTPUT_REG)}, rax
+                mov rax, [rax + 8]
+                mov {c.AsmOut(fr3, t.ASM_DESCR.OUTPUT_REG)}, rax
+                mov rax, [_fault_rbp]
+                mov rax, [rax]
+                mov rax, [rax]
+                mov rax, [rax + 8]
+                mov {c.AsmOut(fr4, t.ASM_DESCR.OUTPUT_REG)}, rax""",
+              op=[t.ASM_DESCR.CLOBBER_RAX])
+        stk_buf: t.CArray[t.CChar, 160]
+        viperlib.snprintf(c.Addr(stk_buf), 160, "[STK] rbp=0x%lx ret: 0x%lx 0x%lx 0x%lx 0x%lx\n",
+                          fr0, fr1, fr2, fr3, fr4)
+        serial.puts(stk_buf)
     elif interrupt == 13:
         gp_rip: t.CUInt64T = 0
         gp_err: t.CUInt64T = 0

VKernel/Kernel/intr/isr.s

@@ -9,6 +9,7 @@
 .comm _fault_rip, 8, 8
 .comm _fault_err, 8, 8
 .comm _fault_rsp, 8, 8
+.comm _fault_rbp, 8, 8
 
 .section .text
 .intel_syntax noprefix
@@ -96,6 +97,7 @@ isr\num\()_frame_ready:
     push rsi
     push rdi
     push rbp
+    mov [_fault_rbp], rbp
     push r8
     push r9
     push r10
@@ -279,6 +281,7 @@ isr\num\()_frame_ready:
     push rsi
     push rdi
     push rbp
+    mov [_fault_rbp], rbp
     push r8
     push r9
     push r10