From 3ab6bb86168e0f6061f32496c1d7cc5d12dab031 Mon Sep 17 00:00:00 2001
From: Ed_ <edwardgz@gmail.com>
Date: Wed, 6 Mar 2024 16:45:12 -0500
Subject: [PATCH] Rolled my own virtual memory baseline interface

Mostly use the core library's functionality but wanted a nicer wrap for my use case
---
 code/grime_virtual_memory.odin | 112 +++++++++++++++++++++++++++++++++
 code/grime_vmem_windows.odin   |  32 ++++++++++
 2 files changed, 144 insertions(+)
 create mode 100644 code/grime_virtual_memory.odin
 create mode 100644 code/grime_vmem_windows.odin

diff --git a/code/grime_virtual_memory.odin b/code/grime_virtual_memory.odin
new file mode 100644
index 0000000..bc9d415
--- /dev/null
+++ b/code/grime_virtual_memory.odin
@@ -0,0 +1,112 @@
+/* Virtual Memory OS Interface
+This is an alternative to the virtual core library provided by odin, suppport setting the base address among other things.
+*/
+package sectr
+
+import core_virtual "core:mem/virtual"
+import "core:os"
+
+VirtualMemoryRegionHeader :: struct {
+	committed     : uint,
+	reserved      : uint,
+	reserve_start : [^]byte,
+}
+
+VirtualMemoryRegion :: struct {
+	using base_address : ^VirtualMemoryRegionHeader
+}
+
+virtual_get_page_size :: proc "contextless" () -> int {
+	@static page_size := 0
+	if page_size == 0 {
+		page_size = os.get_page_size()
+	}
+	return page_size
+}
+
+virtual_reserve_remaining :: proc "contextless" ( using vmem : VirtualMemoryRegion ) -> uint {
+	header_offset := cast(uint) (uintptr(reserve_start) - uintptr(vmem.base_address))
+	return reserved - header_offset
+}
+
+@(require_results)
+virtual_commit :: proc "contextless" ( using vmem : VirtualMemoryRegion, size : uint ) -> ( alloc_error : AllocatorError )
+{
+	if size < committed {
+		return .None
+	}
+
+	page_size := uint(virtual_get_page_size())
+	to_commit := memory_align_formula( size, page_size )
+
+	alloc_error = core_virtual.commit( base_address, to_commit )
+	if alloc_error != .None {
+		return alloc_error
+	}
+
+	base_address.committed = size
+	return alloc_error
+}
+
+virtual_decommit :: proc "contextless" ( vmem : VirtualMemoryRegion, size : uint ) {
+	core_virtual.decommit( vmem.base_address, size )
+}
+
+virtual_protect :: proc "contextless" ( vmem : VirtualMemoryRegion, region : []byte, flags : VirtualProtectFlags ) -> b32
+{
+	page_size := virtual_get_page_size()
+
+	if len(region) % page_size != 0 {
+		return false
+	}
+
+	return cast(b32) core_virtual.protect( raw_data(region), len(region), flags )
+}
+
+@(require_results)
+virtual_reserve :: proc "contextless" ( base_address : uintptr, size : uint ) -> ( VirtualMemoryRegion, AllocatorError ) {
+	page_size  := uint(virtual_get_page_size())
+	to_reserve := memory_align_formula( size, page_size )
+	return virtual__reserve( base_address, to_reserve )
+}
+
+@(require_results)
+virtual_reserve_and_commit :: proc "contextless" (
+	base_address : uintptr, reserve_size, commit_size : uint
+) -> ( vmem : VirtualMemoryRegion, alloc_error : AllocatorError )
+{
+	if reserve_size < commit_size {
+		alloc_error = .Invalid_Argument
+		return
+	}
+
+	vmem, alloc_error = virtual_reserve( base_address, reserve_size )
+	if alloc_error != .None {
+		return
+	}
+
+	alloc_error = virtual_commit( vmem, commit_size )
+	return
+}
+
+virtual_release :: proc "contextless" ( vmem : VirtualMemoryRegion ) {
+	core_virtual.release( vmem.base_address, vmem.reserved )
+}
+
+// If the OS is not windows, we just use the library's interface which does not support base_address.
+when ODIN_OS != OS_Type.Windows {
+
+virtual__reserve :: proc "contextless" ( base_address : uintptr, size : uint ) -> ( vmem : VirtualMemoryRegion, alloc_error : AllocatorError )
+{
+	// Ignoring the base address, add an os specific impl if you want it.
+	data : []byte
+	data, alloc_error := core_virtual.reserve( size ) or_return
+
+	vmem.base_address  := cast( ^VirtualMemoryRegionHeader ) raw_data(data)
+	vmem.reserve_start  = memory_after_header(vmem.base_address)
+	vmem.reserved       = len(data)
+	vmem.committed      = 0
+	return
+}
+
+} // END: ODIN_OS != runtime.Odin_OS_Type.Windows
diff --git a/code/grime_vmem_windows.odin b/code/grime_vmem_windows.odin
new file mode 100644
index 0000000..b16b918
--- /dev/null
+++ b/code/grime_vmem_windows.odin
@@ -0,0 +1,32 @@
+/* Windows Virtual Memory
+Windows is the only os getting special vmem definitions
+since I want full control of it for debug purposes.
+*/
+package sectr
+
+import "core:mem/virtual"
+import win32 "core:sys/windows"
+
+when ODIN_OS == OS_Type.Windows {
+
+@(require_results)
+virtual__reserve ::
+proc "contextless" ( base_address : uintptr, size : uint ) -> ( vmem : VirtualMemoryRegion, alloc_error : AllocatorError )
+{
+	header_size :: cast(uint) size_of(VirtualMemoryRegion)
+
+	result := win32.VirtualAlloc( rawptr(base_address), header_size + size, win32.MEM_RESERVE, win32.PAGE_READWRITE )
+	if result == nil {
+		alloc_error = .Out_Of_Memory
+		return
+	}
+
+	vmem.base_address  = cast(^VirtualMemoryRegionHeader) result
+	vmem.reserve_start = memory_after_header(vmem.base_address)
+	vmem.reserved      = size
+	vmem.committed     = 0
+	alloc_error        = .None
+	return
+}
+
+} // END: ODIN_OS == runtime.Odin_OS_Type.Windows