From afd06491886bd7004f950ca37dd17b14d09e6436 Mon Sep 17 00:00:00 2001
From: DualFroz <me@dualfroz.com>
Date: Wed, 26 Aug 2026 23:10:16 +0200
Subject: [PATCH] feat(loader): add static x86_64 ELF loader

---
 include/elf.h | 36 ++++++++++++++++++++++++++++++++++++
 src/elf.c     | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 87 insertions(+)
 create mode 100644 include/elf.h
 create mode 100644 src/elf.c

diff --git a/include/elf.h b/include/elf.h
new file mode 100644
index 0000000..97fdc25
--- /dev/null
+++ b/include/elf.h
@@ -0,0 +1,36 @@
+#ifndef FROSTBYTE_ELF_H
+#define FROSTBYTE_ELF_H
+
+#include "types.h"
+
+typedef struct Elf64Header {
+    uint8 ident[16];
+    uint16 type;
+    uint16 machine;
+    uint32 version;
+    uint64 entry;
+    uint64 programHeaderOffset;
+    uint64 sectionHeaderOffset;
+    uint32 flags;
+    uint16 headerSize;
+    uint16 programHeaderEntrySize;
+    uint16 programHeaderCount;
+    uint16 sectionHeaderEntrySize;
+    uint16 sectionHeaderCount;
+    uint16 sectionNameIndex;
+} __attribute__((packed)) Elf64Header;
+
+typedef struct Elf64ProgramHeader {
+    uint32 type;
+    uint32 flags;
+    uint64 offset;
+    uint64 virtualAddr;
+    uint64 physicalAddr;
+    uint64 fileSize;
+    uint64 memorySize;
+    uint64 align;
+} __attribute__((packed)) Elf64ProgramHeader;
+
+uint64 elfLoad(const void* image, uint64 imageSize);
+
+#endif
diff --git a/src/elf.c b/src/elf.c
new file mode 100644
index 0000000..450b1fe
--- /dev/null
+++ b/src/elf.c
@@ -0,0 +1,51 @@
+#include "elf.h"
+#include "paging.h"
+#include "string.h"
+#include "console.h"
+
+#define programTypeLoad 1
+#define elfTypeExec 2
+#define elfMachineX8664 62
+
+static bool validHeader(const Elf64Header* header)
+{
+    if (header->ident[0] != 0x7F || header->ident[1] != 'E' ||
+        header->ident[2] != 'L' || header->ident[3] != 'F')
+        return false;
+    if (header->ident[4] != 2)
+        return false;
+    if (header->type != elfTypeExec)
+        return false;
+    if (header->machine != elfMachineX8664)
+        return false;
+    return true;
+}
+
+uint64 elfLoad(const void* image, uint64 imageSize)
+{
+    const Elf64Header* header = (const Elf64Header*)image;
+
+    if (imageSize < sizeof(Elf64Header) || !validHeader(header)) {
+        kprintf("[elf]  rejected image: not a static x86_64 ELF\n");
+        return 0;
+    }
+
+    const uint8* base = (const uint8*)image;
+
+    for (uint16 i = 0; i < header->programHeaderCount; i++) {
+        const Elf64ProgramHeader* segment = (const Elf64ProgramHeader*)
+            (base + header->programHeaderOffset + (uint64)i * header->programHeaderEntrySize);
+
+        if (segment->type != programTypeLoad)
+            continue;
+
+        if (!pagingMapUserRange(segment->virtualAddr, segment->memorySize)) {
+            kprintf("[elf]  failed to map segment at %p\n", (void*)segment->virtualAddr);
+            return 0;
+        }
+
+        memcpy((void*)segment->virtualAddr, base + segment->offset, segment->fileSize);
+    }
+
+    return header->entry;
+}