[kvm-unit-tests PATCH 3/9] x86: desc: Split IDT entry setup into a generic helper

[Varad Gautam <varad.gautam@xxxxxxxx>]

EFI bootstrapping code configures a call gate in a later commit to jump
from 16-bit to 32-bit code.

Introduce a set_idt_entry_t() routine which can be used to fill both
an interrupt descriptor and a call gate descriptor on x86.

Signed-off-by: Varad Gautam <varad.gautam@xxxxxxxx>
---
 lib/x86/desc.c | 28 ++++++++++++++++++++++------
 lib/x86/desc.h |  1 +
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/lib/x86/desc.c b/lib/x86/desc.c
index 355a428..713ad0b 100644
--- a/lib/x86/desc.c
+++ b/lib/x86/desc.c
@@ -56,22 +56,38 @@ __attribute__((regparm(1)))
 #endif
 void do_handle_exception(struct ex_regs *regs);
 
-void set_idt_entry(int vec, void *addr, int dpl)
+/*
+ * Fill an idt_entry_t, clearing e_sz bytes first.
+ *
+ * This can also be used to set up x86 call gates, since the gate
+ * descriptor layout is identical to idt_entry_t, except for the
+ * absence of .offset2 and .reserved fields. To do so, pass in e_sz
+ * according to the gate descriptor size.
+ */
+void set_idt_entry_t(idt_entry_t *e, size_t e_sz, void *addr,
+		u16 sel, u16 type, u16 dpl)
 {
-    idt_entry_t *e = &boot_idt[vec];
-    memset(e, 0, sizeof *e);
+    memset(e, 0, e_sz);
     e->offset0 = (unsigned long)addr;
-    e->selector = read_cs();
+    e->selector = sel;
     e->ist = 0;
-    e->type = 14;
+    e->type = type;
     e->dpl = dpl;
     e->p = 1;
     e->offset1 = (unsigned long)addr >> 16;
 #ifdef __x86_64__
-    e->offset2 = (unsigned long)addr >> 32;
+    if (e_sz == sizeof(*e)) {
+        e->offset2 = (unsigned long)addr >> 32;
+    }
 #endif
 }
 
+void set_idt_entry(int vec, void *addr, int dpl)
+{
+    idt_entry_t *e = &boot_idt[vec];
+    set_idt_entry_t(e, sizeof *e, addr, read_cs(), 14, dpl);
+}
+
 void set_idt_dpl(int vec, u16 dpl)
 {
     idt_entry_t *e = &boot_idt[vec];
diff --git a/lib/x86/desc.h b/lib/x86/desc.h
index 602e9f7..5eb21e4 100644
--- a/lib/x86/desc.h
+++ b/lib/x86/desc.h
@@ -217,6 +217,7 @@ unsigned exception_vector(void);
 int write_cr4_checking(unsigned long val);
 unsigned exception_error_code(void);
 bool exception_rflags_rf(void);
+void set_idt_entry_t(idt_entry_t *e, size_t e_sz, void *addr, u16 sel, u16 type, u16 dpl);
 void set_idt_entry(int vec, void *addr, int dpl);
 void set_idt_sel(int vec, u16 sel);
 void set_idt_dpl(int vec, u16 dpl);
-- 
2.32.0