[librm] Add facility to provide register and stack dump for CPU exceptions

When DEBUG=librm_mgmt is enabled, intercept CPU exceptions and provide
a register and stack dump, then drop to an emergency shell.  Exiting
from the shell will almost certainly not work, but this provides an
opportunity to view the register and stack dump and carry out some
basic debugging.

Note that we can intercept only the first 8 CPU exceptions, since a
PXE ROM is not permitted to rebase the PIC.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

1 files changed, 91 insertions, 1 deletions

diff --git a/src/arch/x86/transitions/librm_mgmt.c b/src/arch/x86/transitions/librm_mgmt.c
index 8144e767..f9e1d261 100644
--- a/src/arch/x86/transitions/librm_mgmt.c
+++ b/src/arch/x86/transitions/librm_mgmt.c
@@ -13,6 +13,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #include <ipxe/profile.h>
 #include <realmode.h>
 #include <pic8259.h>
+#include <ipxe/shell.h>
 
 /*
  * This file provides functions for managing librm.
@@ -43,6 +44,9 @@ struct idtr64 idtr64 = {
 	.limit = ( sizeof ( idt64 ) - 1 ),
 };
 
+/** Length of stack dump */
+#define STACK_DUMP_LEN 128
+
 /** Timer interrupt profiler */
 static struct profiler timer_irq_profiler __profiler = { .name = "irq.timer" };
 
@@ -160,14 +164,100 @@ static struct profiler * interrupt_profiler ( int intr ) {
 }
 
 /**
+ * Display interrupt stack dump (for debugging)
+ *
+ * @v intr		Interrupt number
+ * @v frame32		32-bit interrupt wrapper stack frame (or NULL)
+ * @v frame64		64-bit interrupt wrapper stack frame (or NULL)
+ */
+static __attribute__ (( unused )) void
+interrupt_dump ( int intr, struct interrupt_frame32 *frame32,
+		 struct interrupt_frame64 *frame64 ) {
+	unsigned long sp;
+	void *stack;
+
+	/* Do nothing unless debugging is enabled */
+	if ( ! DBG_LOG )
+		return;
+
+	/* Print register dump */
+	if ( ( sizeof ( physaddr_t ) <= sizeof ( uint32_t ) ) || frame32 ) {
+		sp = ( frame32->esp + sizeof ( *frame32 ) -
+		       offsetof ( typeof ( *frame32 ), esp ) );
+		DBGC ( &intr, "INT%d at %04x:%08x (stack %04x:%08lx):\n",
+		       intr, frame32->cs, frame32->eip, frame32->ss, sp );
+		DBGC ( &intr, "cs = %04x  ds = %04x  es = %04x  fs = %04x  "
+		       "gs = %04x  ss = %04x\n", frame32->cs, frame32->ds,
+		       frame32->es, frame32->fs, frame32->gs, frame32->ss );
+		DBGC ( &intr, "eax = %08x  ebx = %08x  ecx = %08x  "
+		       "edx = %08x  flg = %08x\n", frame32->eax, frame32->ebx,
+		       frame32->ecx, frame32->edx, frame32->eflags );
+		DBGC ( &intr, "esi = %08x  edi = %08x  ebp = %08x  "
+		       "esp = %08lx  eip = %08x\n", frame32->esi, frame32->edi,
+		       frame32->ebp, sp, frame32->eip );
+		stack = ( ( ( void * ) frame32 ) + sizeof ( *frame32 ) );
+	} else {
+		DBGC ( &intr, "INT%d at %04llx:%016llx (stack "
+		       "%04llx:%016llx):\n", intr,
+		       ( ( unsigned long long ) frame64->cs ),
+		       ( ( unsigned long long ) frame64->rip ),
+		       ( ( unsigned long long ) frame64->ss ),
+		       ( ( unsigned long long ) frame64->rsp ) );
+		DBGC ( &intr, "rax = %016llx  rbx = %016llx  rcx = %016llx\n",
+		       ( ( unsigned long long ) frame64->rax ),
+		       ( ( unsigned long long ) frame64->rbx ),
+		       ( ( unsigned long long ) frame64->rcx ) );
+		DBGC ( &intr, "rdx = %016llx  rsi = %016llx  rdi = %016llx\n",
+		       ( ( unsigned long long ) frame64->rdx ),
+		       ( ( unsigned long long ) frame64->rsi ),
+		       ( ( unsigned long long ) frame64->rdi ) );
+		DBGC ( &intr, "rbp = %016llx  rsp = %016llx  flg = %016llx\n",
+		       ( ( unsigned long long ) frame64->rbp ),
+		       ( ( unsigned long long ) frame64->rsp ),
+		       ( ( unsigned long long ) frame64->rflags ) );
+		DBGC ( &intr, "r8  = %016llx  r9  = %016llx  r10 = %016llx\n",
+		       ( ( unsigned long long ) frame64->r8 ),
+		       ( ( unsigned long long ) frame64->r9 ),
+		       ( ( unsigned long long ) frame64->r10 ) );
+		DBGC ( &intr, "r11 = %016llx  r12 = %016llx  r13 = %016llx\n",
+		       ( ( unsigned long long ) frame64->r11 ),
+		       ( ( unsigned long long ) frame64->r12 ),
+		       ( ( unsigned long long ) frame64->r13 ) );
+		DBGC ( &intr, "r14 = %016llx  r15 = %016llx\n",
+		       ( ( unsigned long long ) frame64->r14 ),
+		       ( ( unsigned long long ) frame64->r15 ) );
+		sp = frame64->rsp;
+		stack = phys_to_virt ( sp );
+	}
+
+	/* Print stack dump */
+	DBGC_HDA ( &intr, sp, stack, STACK_DUMP_LEN );
+}
+
+/**
  * Interrupt handler
  *
  * @v intr		Interrupt number
+ * @v frame32		32-bit interrupt wrapper stack frame (or NULL)
+ * @v frame64		64-bit interrupt wrapper stack frame (or NULL)
+ * @v frame		Interrupt wrapper stack frame
  */
-void __attribute__ (( regparm ( 1 ) )) interrupt ( int intr ) {
+void __attribute__ (( regparm ( 3 ) ))
+interrupt ( int intr, struct interrupt_frame32 *frame32,
+	    struct interrupt_frame64 *frame64 ) {
 	struct profiler *profiler = interrupt_profiler ( intr );
 	uint32_t discard_eax;
 
+	/* Trap CPU exceptions if debugging is enabled.  Note that we
+	 * cannot treat INT8+ as exceptions, since we are not
+	 * permitted to rebase the PIC.
+	 */
+	if ( DBG_LOG && ( intr < IRQ_INT ( 0 ) ) ) {
+		interrupt_dump ( intr, frame32, frame64 );
+		DBG ( "CPU exception: dropping to emergency shell\n" );
+		shell();
+	}
+
 	/* Reissue interrupt in real mode */
 	profile_start ( profiler );
 	__asm__ __volatile__ ( REAL_CODE ( "movb %%al, %%cs:(1f + 1)\n\t"