[kvm-unit-tests PATCH v2 1/4] Save/restore handler in test_for_exception

[Jim Mattson <jmattson@xxxxxxxxxx>]

The default handler for #DE, #UD, and #GP is check_exception_table.
Test_for_exception should restore the original handler before
returning, rather than blindly clobbering it with NULL.

Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
---
 lib/x86/desc.c | 16 ++++++++++------
 lib/x86/desc.h |  4 +++-
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/lib/x86/desc.c b/lib/x86/desc.c
index 402204ddcac4..830c5d127dbc 100644
--- a/lib/x86/desc.c
+++ b/lib/x86/desc.c
@@ -117,13 +117,16 @@ static void check_exception_table(struct ex_regs *regs)
     unhandled_exception(regs, false);
 }
 
-static void (*exception_handlers[32])(struct ex_regs *regs);
+static handler exception_handlers[32];
 
-
-void handle_exception(u8 v, void (*func)(struct ex_regs *regs))
+handler handle_exception(u8 v, handler fn)
 {
+	handler old;
+
+	old = exception_handlers[v];
 	if (v < 32)
-		exception_handlers[v] = func;
+		exception_handlers[v] = fn;
+	return old;
 }
 
 #ifndef __x86_64__
@@ -390,14 +393,15 @@ static void exception_handler(struct ex_regs *regs)
 bool test_for_exception(unsigned int ex, void (*trigger_func)(void *data),
 			void *data)
 {
+	handler old;
 	jmp_buf jmpbuf;
 	int ret;
 
-	handle_exception(ex, exception_handler);
+	old = handle_exception(ex, exception_handler);
 	ret = set_exception_jmpbuf(jmpbuf);
 	if (ret == 0)
 		trigger_func(data);
-	handle_exception(ex, NULL);
+	handle_exception(ex, old);
 	return ret;
 }
 
diff --git a/lib/x86/desc.h b/lib/x86/desc.h
index be52fd4e1d92..a2500e0f6006 100644
--- a/lib/x86/desc.h
+++ b/lib/x86/desc.h
@@ -20,6 +20,8 @@ struct ex_regs {
     unsigned long rflags;
 };
 
+typedef void (*handler)(struct ex_regs *regs);
+
 typedef struct {
 	u16 prev;
 	u16 res1;
@@ -153,7 +155,7 @@ void set_idt_dpl(int vec, u16 dpl);
 void set_gdt_entry(int sel, u32 base,  u32 limit, u8 access, u8 gran);
 void set_intr_alt_stack(int e, void *fn);
 void print_current_tss_info(void);
-void handle_exception(u8 v, void (*func)(struct ex_regs *regs));
+handler handle_exception(u8 v, handler fn);
 
 bool test_for_exception(unsigned int ex, void (*trigger_func)(void *data),
 			void *data);
-- 
2.13.2.725.g09c95d1e9-goog