From 0568a813f27344c12f00f65168a02d1d1c698592 Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Fri, 25 Mar 2022 11:53:01 -0400
Subject: [PATCH] HELLO: Zero out HULK bss section

---
 src/hello/hello.d | 51 +++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 45 insertions(+), 6 deletions(-)

diff --git a/src/hello/hello.d b/src/hello/hello.d
index 62bebbf..424a1fa 100644
--- a/src/hello/hello.d
+++ b/src/hello/hello.d
@@ -16,6 +16,7 @@ __gshared EFI_SYSTEM_TABLE * st;
 private __gshared BootInfo bootinfo;
 private __gshared UINTN memory_map_key;
 extern extern(C) __gshared ubyte hulk_bin_start;
+extern extern(C) __gshared ubyte hulk_bin_end;
 
 /**
  * Detect if we're running in QEMU.
@@ -229,6 +230,31 @@ private void map2m(ulong source_page, ulong dest_page, PageTableEntry * pt_base)
     }
 }
 
+/**
+ * Allocate a memory region for the HULK bss section.
+ *
+ * @param bss_size Size of the HULK bss section.
+ *
+ * @return Physical memory address.
+ */
+private ulong alloc_hulk_bss(size_t bss_size)
+{
+    for (size_t i = 0u; i < bootinfo.memory_map_count; i++)
+    {
+        if ((bootinfo.memory_map[i].type == EfiConventionalMemory) &&
+            (bootinfo.memory_map[i].size >= bss_size))
+        {
+            memset64(cast(void *)bootinfo.memory_map[i].base, 0u, bss_size / 8u);
+            return bootinfo.memory_map[i].base;
+        }
+    }
+
+    /* We failed to find free memory. */
+    for (;;)
+    {
+    }
+}
+
 /**
  * Map HULK virtual addresses to physical kernel location.
  *
@@ -237,14 +263,27 @@ private void map2m(ulong source_page, ulong dest_page, PageTableEntry * pt_base)
 private void map_hulk(PageTableEntry * pt_base)
 {
     ulong virt = HULK_VIRTUAL_START;
-    ulong phys = cast(ulong)&hulk_bin_start;
-    HulkHeader * hulk_header = cast(HulkHeader *)&hulk_bin_start;
-    size_t end_phys = phys + cast(size_t)hulk_header.total_size;
-    while (phys < end_phys)
+    ulong hulk_bin_phys_start = cast(ulong)&hulk_bin_start;
+    ulong hulk_bin_phys_end = cast(ulong)&hulk_bin_end;
+    ulong phys_iter = hulk_bin_phys_start;
+    while (phys_iter < hulk_bin_phys_end)
     {
-        map4k(virt, phys, pt_base);
+        map4k(virt, phys_iter, pt_base);
         virt += 4096u;
-        phys += 4096u;
+        phys_iter += 4096u;
+    }
+    /* Now the binary has been mapped, but the bss section still needs to be
+     * allocated, zeroed and mapped. */
+    HulkHeader * hulk_header = cast(HulkHeader *)&hulk_bin_start;
+    size_t hulk_bin_phys_size = hulk_bin_phys_end - hulk_bin_phys_end;
+    size_t bss_size = cast(size_t)hulk_header.total_size - hulk_bin_phys_size;
+    ulong bss_phys = alloc_hulk_bss(bss_size);
+    ulong bss_phys_end = bss_phys + bss_size;
+    while (bss_phys < bss_phys_end)
+    {
+        map4k(virt, bss_phys, pt_base);
+        virt += 4096u;
+        bss_phys += 4096u;
     }
 }