From ac74431a29a8b31d368ad1daba561281e94f46d4 Mon Sep 17 00:00:00 2001
From: Mathias Magnusson <mathias@magnusson.space>
Date: Thu, 29 May 2025 20:48:22 +0200
Subject: create initial simple elf file

---
 src/codegen.zig | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 src/codegen.zig

(limited to 'src/codegen.zig')

diff --git a/src/codegen.zig b/src/codegen.zig
new file mode 100644
index 0000000..da1acd2
--- /dev/null
+++ b/src/codegen.zig
@@ -0,0 +1,51 @@
+const std = @import("std");
+const elf = std.elf;
+const Allocator = std.mem.Allocator;
+const root = @import("root");
+const Block = root.Block;
+
+pub fn create_elf(allocator: Allocator, block: Block) ![]u8 {
+    _ = block;
+
+    const base_addr = 0x10000000;
+    const elf_header: elf.Elf64_Ehdr = .{
+        .e_ident = elf.MAGIC.* ++ [_]u8{
+            elf.ELFCLASS64, // EI_CLASS
+            elf.ELFDATA2LSB, // EI_DATA
+            1, // EI_VERSION
+            @intFromEnum(elf.OSABI.NONE), // EI_OSABI
+            0, // EI_ABIVERSION
+        } ++ [1]u8{0} ** 7, // EI_PAD
+        .e_type = .EXEC,
+        .e_machine = elf.EM.RISCV,
+        .e_version = 1,
+        .e_entry = base_addr + @sizeOf(elf.Elf64_Ehdr) + @sizeOf(elf.Elf64_Phdr), // we place the code directly after the headers
+        .e_phoff = @sizeOf(elf.Elf64_Ehdr), // we place the program header(s) directly after the elf header
+        .e_shoff = 0,
+        .e_flags = 0, // ?
+        .e_ehsize = @sizeOf(elf.Elf64_Ehdr),
+        .e_phentsize = @sizeOf(elf.Elf64_Phdr),
+        .e_phnum = 1,
+        .e_shentsize = @sizeOf(elf.Elf64_Shdr),
+        .e_shnum = 0,
+        .e_shstrndx = 0,
+    };
+    const program_header: elf.Elf64_Phdr = .{
+        .p_type = elf.PT_LOAD,
+        .p_flags = elf.PF_R | elf.PF_X,
+        .p_offset = 0,
+        .p_vaddr = base_addr,
+        .p_paddr = base_addr,
+        .p_filesz = @sizeOf(elf.Elf64_Ehdr) + @sizeOf(elf.Elf64_Phdr) + 40,
+        .p_memsz = @sizeOf(elf.Elf64_Ehdr) + @sizeOf(elf.Elf64_Phdr) + 40,
+        .p_align = 0x1000,
+    };
+
+    var output_buffer: std.ArrayList(u8) = .init(allocator);
+    errdefer output_buffer.deinit();
+    const output = output_buffer.writer();
+    try output.writeAll(std.mem.asBytes(&elf_header));
+    try output.writeAll(std.mem.asBytes(&program_header));
+    for (0..10) |_| try output.writeAll(&std.mem.toBytes(@as(u32, 0x13)));
+    return output_buffer.toOwnedSlice();
+}
-- 
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