From 4aa093034bf8cd439db835515f7e909f2e47492f Mon Sep 17 00:00:00 2001
From: Mathieu Maret <mathieu.maret@gmail.com>
Date: Tue, 26 Oct 2021 21:57:45 +0200
Subject: [PATCH] Page fault: more information

---
 arch/x86/cpu_context.c        | 21 +++++++++++++++++++++
 arch/x86/cpu_context_switch.S | 14 +++++++-------
 arch/x86/exception.c          |  8 ++------
 core/cpu_context.h            |  2 +-
 4 files changed, 31 insertions(+), 14 deletions(-)

diff --git a/arch/x86/cpu_context.c b/arch/x86/cpu_context.c
index 40f77bf..3c8a2ca 100644
--- a/arch/x86/cpu_context.c
+++ b/arch/x86/cpu_context.c
@@ -390,6 +390,27 @@ vaddr_t cpu_context_get_SP(const struct cpu_state *ctxt)
     return (vaddr_t)ctxt;
 }
 
+uint32_t cpu_context_get_EX_err(const struct cpu_state *ctxt)
+{
+    assert(NULL != ctxt);
+
+    /* This is the Err_code of the interrupted context (ie kernel or user
+       context). */
+    return ctxt->error_code;
+}
+
+vaddr_t cpu_context_get_EX_faulting_vaddr(const struct cpu_state *ctxt)
+{
+    assert(NULL != ctxt);
+
+    // A page fault has occurred.
+    // The faulting address is stored in the CR2 register.
+    vaddr_t faulting_address;
+    asm volatile("mov %%cr2, %0" : "=r"(faulting_address));
+
+    return faulting_address;
+}
+
 void cpu_context_dump(const struct cpu_state *ctxt)
 {
     printf("CPU: eip=%x esp=%x eflags=%x cs=%x ds=%x ss=%x err=%x", (unsigned)ctxt->eip,
diff --git a/arch/x86/cpu_context_switch.S b/arch/x86/cpu_context_switch.S
index c043510..7e661f6 100644
--- a/arch/x86/cpu_context_switch.S
+++ b/arch/x86/cpu_context_switch.S
@@ -17,13 +17,13 @@
 .globl cpu_context_switch
 .type cpu_context_switch, @function
 cpu_context_switch:
-        // arg2= to_context    --    esp+68
-        // arg1= from_context  --    esp+64
-        // caller ip           --    esp+60
-  pushf              // (eflags)     esp+56
-  pushl %cs          // (cs)         esp+52
-  pushl $resume_pc   // (ip)         esp+48
-  pushl $0           // (error code) esp+12+8x4
+        // arg2= to_context    --    esp+64
+        // arg1= from_context  --    esp+60
+        // caller ip           --    esp+56
+  pushf              // (eflags)     esp+52
+  pushl %cs          // (cs)         esp+48
+  pushl $resume_pc   // (ip)         esp+44
+  pushl $0           // (error code) esp+12+7x4
   pushl %ebp
   pushl %eax
   pushl %ecx
diff --git a/arch/x86/exception.c b/arch/x86/exception.c
index 5b3d9a8..4aac3df 100644
--- a/arch/x86/exception.c
+++ b/arch/x86/exception.c
@@ -51,14 +51,10 @@ void print_handler(struct cpu_state *frame, ulong intr)
 
 void pagefault_handler(struct cpu_state *frame, ulong intr)
 {
-    // A page fault has occurred.
-    // The faulting address is stored in the CR2 register.
-    uint32_t faulting_address;
-    asm volatile("mov %%cr2, %0" : "=r"(faulting_address));
 
     struct kthread *current = getCurrentThread();
-    printf("page fault while in thread %s at 0x%x 0x%x\n", current->name, faulting_address,
-           cpu_context_get_PC(frame));
+    printf("page fault while in thread %s code at 0x%x when trying to access 0x%x err_code 0x%x\n", current->name,
+           cpu_context_get_PC(frame), cpu_context_get_EX_faulting_vaddr(frame), cpu_context_get_EX_err(frame));
     VGAPrintf(RED, BLACK, 0, VGA_HEIGHT - 1, "PAGE FAULT %d", intr);
     (void)intr;
     for (;;)
diff --git a/core/cpu_context.h b/core/cpu_context.h
index 9d141cc..e17c31b 100644
--- a/core/cpu_context.h
+++ b/core/cpu_context.h
@@ -156,7 +156,7 @@ void cpu_context_dump(const struct cpu_state *ctxt);
  * Return the argument passed by the CPU upon exception, as stored in the
  * saved context
  */
-uint32_t cpu_context_get_EX_info(const struct cpu_state *ctxt);
+uint32_t cpu_context_get_EX_err(const struct cpu_state *ctxt);
 
 /**
  * Return the faulting address of the exception