From e4988a569cdbbbdc70187e80309d496e46225b73 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Wed, 13 Dec 2023 12:47:10 -0500
Subject: kernel/amd64: tss: Add TSS stack helpers

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/arch/amd64/tss.c         | 74 ++++++++++++++++++++++++++++++++++++++++++++
 sys/include/arch/amd64/tss.h | 14 +++++++++
 2 files changed, 88 insertions(+)

diff --git a/sys/arch/amd64/tss.c b/sys/arch/amd64/tss.c
index ba1b0f6..b1b5420 100644
--- a/sys/arch/amd64/tss.c
+++ b/sys/arch/amd64/tss.c
@@ -32,6 +32,8 @@
 #include <lib/string.h>
 #include <vm/dynalloc.h>
 #include <sys/panic.h>
+#include <sys/errno.h>
+#include <assert.h>
 
 __MODULE_NAME("TSS");
 __KERNEL_META("$Hyra$: tss.c, Ian Marco Moffett, "
@@ -55,6 +57,78 @@ alloc_resources(struct cpu_info *cpu)
     }
 }
 
+/*
+ * Update interrupt stack table entry `istno' with `stack'
+ *
+ * @stack: Interrupt stack.
+ * @istno: IST number, must be 1-based.
+ *
+ * Returns 0 on success.
+ */
+int
+tss_update_ist(struct cpu_info *ci, union tss_stack stack, uint8_t istno)
+{
+    volatile struct tss_entry *tss = ci->tss;
+
+    __assert(tss != NULL);
+
+    switch (istno) {
+    case 1:
+        tss->ist1_lo = stack.top_lo;
+        tss->ist1_hi = stack.top_hi;
+        break;
+    case 2:
+        tss->ist2_lo = stack.top_lo;
+        tss->ist2_hi = stack.top_hi;
+        break;
+    case 3:
+        tss->ist3_lo = stack.top_lo;
+        tss->ist3_hi = stack.top_hi;
+        break;
+    case 4:
+        tss->ist4_lo = stack.top_lo;
+        tss->ist4_hi = stack.top_hi;
+        break;
+    case 5:
+        tss->ist5_lo = stack.top_lo;
+        tss->ist5_hi = stack.top_hi;
+        break;
+    case 6:
+        tss->ist6_lo = stack.top_lo;
+        tss->ist6_hi = stack.top_hi;
+        break;
+    case 7:
+        tss->ist7_lo = stack.top_lo;
+        tss->ist7_hi = stack.top_hi;
+        break;
+    default:
+        return -EXIT_FAILURE;
+    };
+
+    return 0;
+}
+
+/*
+ * Allocates TSS stack.
+ *
+ * Returns 0 on success.
+ *
+ * @entry_out: Pointer to location where allocated entry
+ *             will be sent.
+ */
+int
+tss_alloc_stack(union tss_stack *entry_out, size_t size)
+{
+    uintptr_t base = (uintptr_t)dynalloc(size);
+
+    if (base == 0) {
+        return -EXIT_FAILURE;
+    }
+
+    entry_out->top = base + size;
+    return 0;
+}
+
 void
 write_tss(struct cpu_info *cpu, struct tss_desc *desc)
 {
diff --git a/sys/include/arch/amd64/tss.h b/sys/include/arch/amd64/tss.h
index 90f6289..bca572e 100644
--- a/sys/include/arch/amd64/tss.h
+++ b/sys/include/arch/amd64/tss.h
@@ -100,6 +100,20 @@ struct __packed tss_desc {
     uint32_t reserved;
 };
 
+/*
+ * Holds the address of the address pointing
+ * to the top of an interrupt stack.
+ */
+union tss_stack {
+    struct {
+        uint32_t top_lo;
+        uint32_t top_hi;
+    };
+    uint64_t top;
+};
+
+int tss_alloc_stack(union tss_stack *entry_out, size_t size);
+int tss_update_ist(struct cpu_info *ci, union tss_stack stack, uint8_t istno);
 void write_tss(struct cpu_info *cpu, struct tss_desc *desc);
 void tss_load(void);        /* In tss.S */
 
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