[PATCH 1/6 gnumach] Fix apic_send_ipi function clobbering read only fields

[Damien Zammit]

This was the root cause of failing to INIT.
We were clobbering remote_read_status.
And also, we need to reference the .r register
when writing the ICR regs otherwise I think
it writes all of the block.
---
 i386/i386/apic.c | 8 ++++++--
 i386/i386/apic.h | 2 +-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/i386/i386/apic.c b/i386/i386/apic.c
index 0cf7c37c..700fafd3 100644
--- a/i386/i386/apic.c
+++ b/i386/i386/apic.c
@@ -290,6 +290,10 @@ void apic_send_ipi(unsigned dest_shorthand, unsigned 
deliv_mode, unsigned dest_m
     IcrLReg icrl_values;
     IcrHReg icrh_values;
 
+    /* Keep previous values and only overwrite known fields */
+    icrl_values.r = lapic->icr_low.r;
+    icrh_values.r = lapic->icr_high.r;
+
     icrl_values.destination_shorthand = dest_shorthand;
     icrl_values.delivery_mode = deliv_mode;
     icrl_values.destination_mode = dest_mode;
@@ -298,8 +302,8 @@ void apic_send_ipi(unsigned dest_shorthand, unsigned 
deliv_mode, unsigned dest_m
     icrl_values.vector = vector;
     icrh_values.destination_field = dest_id;
 
-    lapic->icr_high = icrh_values;
-    lapic->icr_low = icrl_values;
+    lapic->icr_high.r = icrh_values.r;
+    lapic->icr_low.r = icrl_values.r;
 }
 
 void
diff --git a/i386/i386/apic.h b/i386/i386/apic.h
index e410e9c6..e1d49895 100644
--- a/i386/i386/apic.h
+++ b/i386/i386/apic.h
@@ -83,7 +83,7 @@ typedef union u_icr_low
         unsigned :1;
         unsigned level: 1;
         unsigned trigger_mode: 1;
-        unsigned :2;
+        unsigned remote_read_status: 2;        /* Read-only field */
         unsigned destination_shorthand: 2;
         unsigned :12;
     };
-- 
2.43.0