Build relocation stub from source

meson.build

@@ -30,18 +30,22 @@ dols = {}
 # executable to `dols`.
 compressed_exes = {}
 
+subdir('stub')
+
 linker_script = meson.current_source_dir() / 'ogc.ld'
 
 iplboot = executable(
     'iplboot',
     'source/main.c',
-    'source/stub.c',
     'source/utils.c',
     'source/fatfs/ff.c',
     'source/fatfs/ffsystem.c',
     'source/fatfs/ffunicode.c',
     'source/ffshim.c',
-    dependencies: libogc_deps['ogc'],
+    dependencies: [
+        libogc_deps['ogc'],
+        stub_dep,
+    ],
     link_args: ['-T' + linker_script],
     link_depends: [linker_script],
     name_suffix: 'elf',

ogc.ld

@@ -91,7 +91,14 @@ SECTIONS
 	PROVIDE (_etext = .);
 	PROVIDE (etext = .);
 
-	.rodata   : { *(.rodata) *(.rodata.*) *(.gnu.linkonce.r.*) } :data
+	.rodata   : {
+		*(.rodata) *(.rodata.*)
+		*(.gnu.linkonce.r.*)
+
+		stub = .;
+		KEEP(*(reloc_stub.data))
+		__stub_end = .;
+	} :data
 	.rodata1   : { *(.rodata1) }
 	.sdata2   : { 
 		PROVIDE(_SDA2_BASE_ = . );
@@ -270,3 +277,7 @@ __Arena1Lo = (__intrstack_addr + 31) & (-32);
 __Arena1Hi = (0x81700000);
 
 __xfb = ((__Arena1Hi + 31) & (-32)) + (0xC0000000 - 0x80000000);
+
+stub_size = __stub_end - stub;
+ASSERT(stub_size > 0, "Relocation stub missing!")
+ASSERT(stub_size <= 0x300, "Relocation stub too big!")

source/main.c

@@ -12,8 +12,6 @@
 #include "utils.h"
 
 #include "stub.h"
-#define STUB_ADDR  0x80001000
-#define STUB_STACK 0x80003000
 
 #define VERBOSE_LOGGING 0
 
@@ -450,8 +448,8 @@ int main()
         }
     }
 
-    memcpy((void *) STUB_ADDR, stub, stub_size);
-    DCStoreRange((void *) STUB_ADDR, stub_size);
+    memcpy((void *) STUB_ADDR, stub, (size_t) stub_size);
+    DCStoreRange((void *) STUB_ADDR, (u32) stub_size);
 
     delay_exit();
 

stub/link.ld

@@ -0,0 +1,21 @@
+OUTPUT_FORMAT("elf32-powerpc")
+OUTPUT_ARCH(powerpc:common)
+ENTRY(not_main)
+
+PHDRS
+{
+	stub PT_LOAD FLAGS(5);
+	text PT_LOAD FLAGS(5);
+	data PT_LOAD FLAGS(6);
+	bss  PT_LOAD FLAGS(6);
+}
+
+SECTIONS
+{
+	. = ALIGN(32);
+	.text :
+	{
+		*(.text.not_main)
+		*(.text .text.*)
+	} : text
+}

stub/meson.build

@@ -0,0 +1,49 @@
+stub_linker_script = meson.current_source_dir() / 'link.ld'
+
+stub_exe = executable(
+    'stub',
+    'stub.c',
+    c_args: [
+        '-fPIC',
+        '-ffreestanding',
+        '-mno-eabi',
+    ],
+    link_args: [
+        '-nostdlib',
+        '-T' + stub_linker_script,
+    ],
+    link_depends: stub_linker_script,
+    dependencies: [
+        # For the headers
+        libogc_deps['ogc'].partial_dependency(
+            compile_args: true,
+            sources: true,
+        ),
+    ],
+)
+
+stub_bin = custom_target(
+    'stub_bin',
+    input: stub_exe,
+    output: 'stub.bin',
+    command: [objcopy, '-O', 'binary', '@INPUT@', '@OUTPUT@'],
+)
+
+stub_o = custom_target(
+    'stub_o',
+    input: stub_bin,
+    output: 'stub.o',
+    command: [
+        objcopy,
+        '-I', 'binary',
+        '-O', 'default',
+        '@INPUT@',
+        '@OUTPUT@',
+        '--prefix-sections=reloc_stub',
+    ],
+)
+
+stub_dep = declare_dependency(
+    sources: stub_o,
+    include_directories: '.',
+)

stub/stub.c

@@ -0,0 +1,97 @@
+/*
+ * Copyright (c) 2014-2023, Extrems' Corner.org
+ * All rights reserved.
+ */
+
+#include <ogc/system.h>
+#include <ogc/machine/processor.h>
+
+typedef struct {
+	ptrdiff_t section_offset[18];
+
+	void *section[18];
+	size_t section_size[18];
+
+	void *bss;
+	size_t bss_size;
+
+	void (*entrypoint)(void);
+} dol_header_t;
+
+static void memsync(void *buf, size_t size)
+{
+	uint8_t *b = buf;
+	size_t i;
+
+	for (i = 0; i < size; i += PPC_CACHE_ALIGNMENT)
+		asm("dcbst %y0" :: "Z" (b[i]));
+}
+
+static void memzero(void *buf, size_t size)
+{
+	uint8_t *b = buf;
+	uint8_t *e = b + size;
+
+	while (b != e)
+		*b++ = '\0';
+}
+
+static void *memmove(void *dest, const void *src, size_t size)
+{
+	uint8_t *d = dest;
+	const uint8_t *s = src;
+	size_t i;
+
+	if (d < s) {
+		for (i = 0; i < size; ++i)
+			d[i] = s[i];
+	} else if (d > s) {
+		i = size;
+		while (i-- > 0)
+			d[i] = s[i];
+	}
+
+	return dest;
+}
+
+// Workaround for GCC bug 5372 – [powerpc-*-eabi] -mno-eabi not working
+// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=5372
+// Entry point can't be called main or GCC will insert a call to __eabi
+__attribute__((noreturn)) void not_main(const void *buf, size_t buflen, const void *arg, size_t arglen)
+{
+	dol_header_t header;
+	uint32_t *entrypoint;
+	uint8_t args[arglen];
+
+	memmove(&header, buf, sizeof(dol_header_t));
+	memmove(args, arg, arglen);
+
+	if (header.section[0] < buf + header.section_offset[0]) {
+		for (int i = 0; i < 18; i++) {
+			memmove(header.section[i], buf + header.section_offset[i], header.section_size[i]);
+			memsync(header.section[i], header.section_size[i]);
+		}
+	} else {
+		for (int i = 18; i > 0; i--) {
+			memmove(header.section[i - 1], buf + header.section_offset[i - 1], header.section_size[i - 1]);
+			memsync(header.section[i - 1], header.section_size[i - 1]);
+		}
+	}
+
+	memzero(header.bss, header.bss_size);
+	memsync(header.bss, header.bss_size);
+
+	entrypoint = MEM_K0_TO_K1(header.entrypoint);
+
+	if (entrypoint[1] == ARGV_MAGIC && arglen) {
+		entrypoint[2]  = ARGV_MAGIC;
+		entrypoint[3]  = (intptr_t)args;
+		entrypoint[4]  = arglen;
+	}
+
+	_sync();
+	mthid0(mfhid0() | 0xC00);
+	header.entrypoint();
+
+	__builtin_unreachable();
+}

stub/stub.h

@@ -0,0 +1,9 @@
+#pragma once
+
+#include <stdint.h>
+
+#define STUB_ADDR  0x80001000
+#define STUB_STACK 0x80003000
+
+extern const uint8_t stub[];
+extern const uint8_t stub_size[];