From 222e23c6786e0ac307524c6c91b41782111af82a Mon Sep 17 00:00:00 2001
From: Noam Preil <noam@pixelhero.dev>
Date: Fri, 21 Aug 2020 07:25:21 -0400
Subject: [PATCH] Linker: make defaults read-only

---
 src-self-hosted/link.zig     |  2 +-
 src-self-hosted/link/Elf.zig | 15 ++++++---------
 2 files changed, 7 insertions(+), 10 deletions(-)

diff --git a/src-self-hosted/link.zig b/src-self-hosted/link.zig
index e8604038c2..59b01dc762 100644
--- a/src-self-hosted/link.zig
+++ b/src-self-hosted/link.zig
@@ -23,7 +23,7 @@ pub const Options = struct {
     /// Used for calculating how much space to reserve for executable program code in case
     /// the binary file deos not already have such a section.
     program_code_size_hint: u64 = 256 * 1024,
-    default_entry_addr: u64 = 0x8000000,
+    entry_addr: ?u64 = null,
 };
 
 pub const File = struct {
diff --git a/src-self-hosted/link/Elf.zig b/src-self-hosted/link/Elf.zig
index 34f2243718..53798053c2 100644
--- a/src-self-hosted/link/Elf.zig
+++ b/src-self-hosted/link/Elf.zig
@@ -286,10 +286,6 @@ fn createFile(allocator: *Allocator, file: fs.File, options: link.Options) !Elf
     };
     errdefer self.deinit();
 
-    if (options.target.cpu.arch == .spu_2) {
-        self.base.options.default_entry_addr = 0;
-    }
-
     // Index 0 is always a null symbol.
     try self.local_symbols.append(allocator, .{
         .st_name = 0,
@@ -466,12 +462,13 @@ pub fn populateMissingMetadata(self: *Elf) !void {
         const p_align = 0x1000;
         const off = self.findFreeSpace(file_size, p_align);
         log.debug("found PT_LOAD free space 0x{x} to 0x{x}\n", .{ off, off + file_size });
+        const entry_addr: u64 = self.entry_addr orelse if (self.base.options.target.cpu.arch == .spu_2) @as(u64, 0) else default_entry_addr;
         try self.program_headers.append(self.base.allocator, .{
             .p_type = elf.PT_LOAD,
             .p_offset = off,
             .p_filesz = file_size,
-            .p_vaddr = self.base.options.default_entry_addr,
-            .p_paddr = self.base.options.default_entry_addr,
+            .p_vaddr = entry_addr,
+            .p_paddr = entry_addr,
             .p_memsz = file_size,
             .p_align = p_align,
             .p_flags = elf.PF_X | elf.PF_R,
@@ -490,13 +487,13 @@ pub fn populateMissingMetadata(self: *Elf) !void {
         // TODO instead of hard coding the vaddr, make a function to find a vaddr to put things at.
         // we'll need to re-use that function anyway, in case the GOT grows and overlaps something
         // else in virtual memory.
-        const default_got_addr = if (self.base.options.target.cpu.arch.ptrBitWidth() == 16) @as(u32, 0x8000) else 0x4000000;
+        const got_addr = if (self.base.options.target.cpu.arch.ptrBitWidth() == 16) @as(u32, 0x8000) else 0x4000000;
         try self.program_headers.append(self.base.allocator, .{
             .p_type = elf.PT_LOAD,
             .p_offset = off,
             .p_filesz = file_size,
-            .p_vaddr = default_got_addr,
-            .p_paddr = default_got_addr,
+            .p_vaddr = got_addr,
+            .p_paddr = got_addr,
             .p_memsz = file_size,
             .p_align = p_align,
             .p_flags = elf.PF_R,