From 9ee8c2c75f4e83b692ad8e4491e18b0bf0906a24 Mon Sep 17 00:00:00 2001
From: Ben Gras <ben@minix3.org>
Date: Fri, 4 Jan 2013 18:26:10 +0000
Subject: [PATCH] kernel: restore stacktraces

When processes have entered the kernel with one of the new
trap modes, %ebp is not valid, used for stacktraces, so we
need an alternative way to retrieve it to make the stacktraces
valid again.
---
 kernel/arch/i386/exception.c          | 37 ++++++++++++++++++++++++++-
 kernel/arch/i386/usermapped_glo_ipc.S |  6 +++++
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/kernel/arch/i386/exception.c b/kernel/arch/i386/exception.c
index d885cfcd1..3a4064d8d 100644
--- a/kernel/arch/i386/exception.c
+++ b/kernel/arch/i386/exception.c
@@ -312,8 +312,43 @@ static void proc_stacktrace_execute(struct proc *whichproc, reg_t v_bp, reg_t pc
  *===========================================================================*/
 void proc_stacktrace(struct proc *whichproc)
 {
+	u32_t use_bp;
+
+	if(whichproc->p_seg.p_kern_trap_style == KTS_NONE) {
+		printf("WARNING: stacktrace of running proecss\n");
+	}
+
+	switch(whichproc->p_seg.p_kern_trap_style) {
+		case KTS_SYSENTER:
+		case KTS_SYSCALL:
+		{
+			u32_t sp = whichproc->p_reg.sp;
+
+			/* Full context is not available in the p_reg
+			 * struct. Obtain it from the user's stack.
+			 * The use stack pointer is always available.
+			 * The fact that it's there, and the 16 byte offset,
+			 * is a dependency on the trap code in
+			 * kernel/arch/i386/usermapped_glo_ipc.S.
+			 */
+
+			if(data_copy(whichproc->p_endpoint, sp+16,
+			  KERNEL, (vir_bytes) &use_bp,
+				sizeof(use_bp)) != OK) {
+				printf("stacktrace: aborting, copy failed\n");
+				return;
+			}
+
+			break;
+		}
+		default:
+			/* Full context is available; use the stored ebp */
+			use_bp = whichproc->p_reg.fp;
+			break;
+	}
+
 #if USE_SYSDEBUG
-	proc_stacktrace_execute(whichproc, whichproc->p_reg.fp, whichproc->p_reg.pc);
+	proc_stacktrace_execute(whichproc, use_bp, whichproc->p_reg.pc);
 #endif /* USE_SYSDEBUG */
 }
 
diff --git a/kernel/arch/i386/usermapped_glo_ipc.S b/kernel/arch/i386/usermapped_glo_ipc.S
index 3df59df36..72d9bb8a9 100644
--- a/kernel/arch/i386/usermapped_glo_ipc.S
+++ b/kernel/arch/i386/usermapped_glo_ipc.S
@@ -29,6 +29,9 @@ ENTRY(usermapped_ ## name ## _sysenter)					;\
 	movl	%esp, %esi	/* kernel uses %esi for restored %esp */;\
 	movl	$0f, %edx	/* kernel uses %edx for restored %eip */;\
 	movl	$VEC, %edi	/* %edi to distinguish ipc/kerncall */	;\
+	/* !!! There is a dependency of proc_stacktrace()		;\
+	 * on this stack layout; it needs to find %ebp on it.		;\
+	 */								;\
 	SETARGS			/* call-specific register setup */	;\
 	sysenter		/* disappear into kernel */		;\
 0:									;\
@@ -50,6 +53,9 @@ ENTRY(usermapped_ ## name ## _syscall)					;\
 	push	%esi							;\
 	push	%edi							;\
 	movl	$VEC, %edi	/* %edi to distinguish ipc/kerncall */	;\
+	/* !!! There is a dependency of proc_stacktrace()		;\
+	 * on this stack layout; it needs to find %ebp on it.		;\
+	 */								;\
 	SETARGS			/* call-specific register setup */	;\
 	movl	%ecx, %edx	/* %ecx is clobbered by SYSCALL */	;\
 	syscall			/* disappear into kernel */		;\