kernel: Binary code patches on x86.

This will be used to support SMAP.

Sponsored-by:	https://liberapay.com/korli

headers/private/kernel/arch/x86/arch_altcodepatch.h

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2018, Jérôme Duval, [email protected].
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef _KERNEL_ARCH_x86_ALTCODEPATCH_H
+#define _KERNEL_ARCH_x86_ALTCODEPATCH_H
+
+
+#include <arch/x86/arch_kernel.h>
+
+
+#define ASM_NOP1	.byte 0x90
+#define ASM_NOP2	.byte 0x66, 0x90
+#define ASM_NOP3	.byte 0x0f, 0x1f, 0x00
+#define ASM_NOP4	.byte 0x0f, 0x1f, 0x40, 0x00
+#define ASM_NOP5	.byte 0x0f, 0x1f, 0x44, 0x00, 0x00
+#define ASM_NOP6	.byte 0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00
+#define ASM_NOP7	.byte 0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00
+#define ASM_NOP8	.byte 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00
+#define ASM_NOP9	.byte 0x66, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00
+
+
+#ifdef _ASSEMBLER
+
+#define CODEPATCH_START	990:
+#define CODEPATCH_END(tag)	991:	\
+	.pushsection	.altcodepatch, "a"	;	\
+	.long			(990b - KERNEL_LOAD_BASE)	;	\
+	.short			(991b - 990b)		;	\
+	.short			tag				;	\
+	.popsection
+
+#else
+
+#define _STRINGIFY(x...)	#x
+#define STRINGIFY(x...)		_STRINGIFY(x)
+
+#define CODEPATCH_START	"990:	\n"
+#define CODEPATCH_END(tag)	"991:	\n"	\
+	".pushsection	.altcodepatch, \"a\"	\n" \
+	".long			(990b - " STRINGIFY(KERNEL_LOAD_BASE) ")	\n" \
+	".short			(991b - 990b)		\n" \
+	".short			" STRINGIFY(tag)	"	\n" \
+	".popsection"
+
+void arch_altcodepatch_replace(uint16 tag, void* newcodepatch, size_t length);
+
+
+#endif
+
+#endif	/* _KERNEL_ARCH_x86_ALTCODEPATCH_H */

src/system/kernel/arch/x86/Jamfile

@@ -72,6 +72,7 @@ if $(TARGET_ARCH) = x86_64 {
 }
 
 local archGenericSources =
+	arch_altcodepatch.cpp
 	arch_cpu.cpp
 	arch_commpage.cpp
 	arch_debug.cpp

src/system/kernel/arch/x86/arch_altcodepatch.cpp

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2018, Jérôme Duval, [email protected].
+ * Distributed under the terms of the MIT License.
+ */
+
+
+#include "arch/x86/arch_altcodepatch.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+#include <KernelExport.h>
+
+#include <kernel.h>
+
+
+
+typedef struct altcodepatch {
+	uint32 kernel_offset;
+	uint16 length;
+	uint16 tag;
+} altcodepatch;
+
+
+extern altcodepatch altcodepatch_begin;
+extern altcodepatch altcodepatch_end;
+
+
+void
+arch_altcodepatch_replace(uint16 tag, void* newcodepatch, size_t length)
+{
+	uint32	count = 0;
+
+	for (altcodepatch *patch = &altcodepatch_begin; patch < &altcodepatch_end;
+		patch++) {
+		if (patch->tag != tag)
+			continue;
+		addr_t address = KERNEL_LOAD_BASE + patch->kernel_offset;
+		if (patch->length < length)
+			panic("can't copy patch: new code is too long\n");
+		memcpy((void*)address, newcodepatch, length);
+		count++;
+	}
+	dprintf("arch_altcodepatch_replace found %d altcodepatches\n", count);
+}
+
+
+

src/system/ldscripts/x86/kernel.ld

@@ -39,6 +39,11 @@ SECTIONS
 
 	.rodata : { *(.rodata) }
 
+	. = ALIGN(0x4);
+	altcodepatch_begin = .;
+	.altcodepatch : { *(.altcodepatch) }
+	altcodepatch_end = .;
+
 	/* writable data  */
 	. = ALIGN(0x1000);
 	__data_start = .;

src/system/ldscripts/x86_64/kernel.ld

@@ -28,6 +28,11 @@ SECTIONS
 
 	.rodata : { *(.rodata .rodata.* .gnu.linkonce.r.*) }
 
+	. = ALIGN(0x8);
+	altcodepatch_begin = .;
+	.altcodepatch : { *(.altcodepatch) }
+	altcodepatch_end = .;
+
 	/* writable data */
 	. = ALIGN (0x1000);
 	__data_start = .;