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Subject[PATCH 01/22] ARM: add mechanism for late code patching
Date
The original phys_to_virt/virt_to_phys patching implementation relied on early
patching prior to MMU initialization. On PAE systems running out of >4G
address space, this would have entailed an additional round of patching after
switching over to the high address space.

The approach implemented here conceptually extends the original PHYS_OFFSET
patching implementation with the introduction of "early" patch stubs. Early
patch code is required to be functional out of the box, even before the patch
is applied. This is implemented by inserting functional (but inefficient)
load code into the .patch.code init section. Having functional code out of
the box then allows us to defer the init time patch application until later
in the init sequence.

In addition to fitting better with our need for physical address-space
switch-over, this implementation should be somewhat more extensible by virtue
of its more readable (and hackable) C implementation. This should prove
useful for other similar init time specialization needs, especially in light
of our multi-platform kernel initiative.

This code has been boot tested in both ARM and Thumb-2 modes on an ARMv7
(Cortex-A8) device.

Note: the obtuse use of stringified symbols in patch_stub() and
early_patch_stub() is intentional. Theoretically this should have been
accomplished with formal operands passed into the asm block, but this requires
the use of the 'c' modifier for instantiating the long (e.g. .long %c0).
However, the 'c' modifier has been found to ICE certain versions of GCC, and
therefore we resort to stringified symbols here.

Signed-off-by: Cyril Chemparathy <cyril@ti.com>
---
arch/arm/include/asm/patch.h | 123 +++++++++++++++++++++++++++++
arch/arm/kernel/module.c | 4 +
arch/arm/kernel/setup.c | 175 +++++++++++++++++++++++++++++++++++++++++
arch/arm/kernel/vmlinux.lds.S | 10 +++
4 files changed, 312 insertions(+)
create mode 100644 arch/arm/include/asm/patch.h

diff --git a/arch/arm/include/asm/patch.h b/arch/arm/include/asm/patch.h
new file mode 100644
index 0000000..a89749f
--- /dev/null
+++ b/arch/arm/include/asm/patch.h
@@ -0,0 +1,123 @@
+/*
+ * arch/arm/include/asm/patch.h
+ *
+ * Copyright (C) 2012, Texas Instruments
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Note: this file should not be included by non-asm/.h files
+ */
+#ifndef __ASM_ARM_PATCH_H
+#define __ASM_ARM_PATCH_H
+
+#include <linux/stringify.h>
+
+#ifndef __ASSEMBLY__
+
+extern unsigned __patch_table_begin, __patch_table_end;
+
+struct patch_info {
+ u32 type;
+ u32 size;
+ void *insn_start;
+ void *insn_end;
+ u32 patch_data[0];
+};
+
+#define patch_next(p) ((void *)(p) + (p)->size)
+
+#define PATCH_TYPE_MASK 0xffff
+#define PATCH_IMM8 0x0001
+
+#define PATCH_EARLY 0x10000
+
+#define patch_stub(type, code, patch_data, ...) \
+ __asm__("@ patch stub\n" \
+ "1:\n" \
+ code \
+ "2:\n" \
+ " .pushsection .patch.table, \"a\"\n" \
+ "3:\n" \
+ " .long (" __stringify(type) ")\n" \
+ " .long (4f-3b)\n" \
+ " .long 1b\n" \
+ " .long 2b\n" \
+ patch_data \
+ "4:\n" \
+ " .popsection\n" \
+ __VA_ARGS__)
+
+#define early_patch_stub(type, code, patch_data, ...) \
+ __asm__("@ patch stub\n" \
+ "1:\n" \
+ " b 5f\n" \
+ "2:\n" \
+ " .pushsection .patch.table, \"a\"\n" \
+ "3:\n" \
+ " .long (" __stringify(type | PATCH_EARLY) ")\n" \
+ " .long (4f-3b)\n" \
+ " .long 1b\n" \
+ " .long 2b\n" \
+ patch_data \
+ "4:\n" \
+ " .popsection\n" \
+ " .pushsection .patch.code, \"ax\"\n" \
+ "5:\n" \
+ code \
+ " b 2b\n" \
+ " .popsection\n" \
+ __VA_ARGS__)
+
+/* constant used to force encoding */
+#define __IMM8 (0x81 << 24)
+
+/*
+ * patch_imm8() - init-time specialized binary operation (imm8 operand)
+ * This effectively does: to = from "insn" sym,
+ * where the value of sym is fixed at init-time, and is patched
+ * in as an immediate operand. This value must be
+ * representible as an 8-bit quantity with an optional
+ * rotation.
+ *
+ * The stub code produced by this variant is non-functional
+ * prior to patching. Use early_patch_imm8() if you need the
+ * code to be functional early on in the init sequence.
+ */
+#define patch_imm8(from, to, insn, sym) \
+ patch_stub(PATCH_IMM8, \
+ /* code */ \
+ insn " %0, %1, %2\n", \
+ /* patch_data */ \
+ ".long " __stringify(sym) "\n" \
+ insn " %0, %1, %2\n", \
+ : "=r" (to) \
+ : "r" (from), "I" (__IMM8), "m" (sym) \
+ : "cc")
+
+/*
+ * early_patch_imm8() - early functional variant of patch_imm8() above. The
+ * same restrictions on the constant apply here. This
+ * version emits workable (albeit inefficient) code at
+ * compile-time, and therefore functions even prior to
+ * patch application.
+ */
+#define early_patch_imm8(from, to, insn, sym) \
+ early_patch_stub(PATCH_IMM8, \
+ /* code */ \
+ "ldr %0, =" __stringify(sym) "\n" \
+ "ldr %0, [%0]\n" \
+ insn " %0, %1, %0\n", \
+ /* patch_data */ \
+ ".long " __stringify(sym) "\n" \
+ insn " %0, %1, %2\n", \
+ : "=&r" (to) \
+ : "r" (from), "I" (__IMM8), "m" (sym) \
+ : "cc")
+
+int patch_kernel(const void *table, unsigned size);
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* __ASM_ARM_PATCH_H */
diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
index 1e9be5d..df5e897 100644
--- a/arch/arm/kernel/module.c
+++ b/arch/arm/kernel/module.c
@@ -24,6 +24,7 @@
#include <asm/sections.h>
#include <asm/smp_plat.h>
#include <asm/unwind.h>
+#include <asm/patch.h>

#ifdef CONFIG_XIP_KERNEL
/*
@@ -321,6 +322,9 @@ int module_finalize(const Elf32_Ehdr *hdr, const Elf_Shdr *sechdrs,
if (s)
fixup_pv_table((void *)s->sh_addr, s->sh_size);
#endif
+ s = find_mod_section(hdr, sechdrs, ".patch.table");
+ if (s)
+ patch_kernel((void *)s->sh_addr, s->sh_size);
s = find_mod_section(hdr, sechdrs, ".alt.smp.init");
if (s && !is_smp())
#ifdef CONFIG_SMP_ON_UP
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index e15d83b..15a7699 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -55,6 +55,7 @@
#include <asm/traps.h>
#include <asm/unwind.h>
#include <asm/memblock.h>
+#include <asm/opcodes.h>

#if defined(CONFIG_DEPRECATED_PARAM_STRUCT)
#include "compat.h"
@@ -937,6 +938,178 @@ static int __init meminfo_cmp(const void *_a, const void *_b)
return cmp < 0 ? -1 : cmp > 0 ? 1 : 0;
}

+static int apply_patch_imm8_arm(const struct patch_info *p)
+{
+ u32 insn, ninsn, op, *insn_ptr = p->insn_start;
+ u32 imm, rot, val;
+ int size = p->insn_end - p->insn_start;
+
+ if (size != 4) {
+ pr_err("patch: bad template size %d\n", size);
+ return -EINVAL;
+ }
+
+ insn = __mem_to_opcode_arm(p->patch_data[1]);
+
+ /* disallow special unconditional instructions
+ * 1111 xxxx xxxx xxxx xxxx xxxx xxxx xxxx */
+ if ((insn >> 24) == 0xf) {
+ pr_err("patch: unconditional insn %08x\n", insn);
+ return -EINVAL;
+ }
+
+ /* allow only data processing (immediate)
+ * xxxx 001x xxxx xxxx xxxx xxxx xxxx xxxx */
+ if (((insn >> 25) & 0x3) != 1) {
+ pr_err("patch: unknown insn %08x\n", insn);
+ return -EINVAL;
+ }
+
+ /* extract op code */
+ op = (insn >> 20) & 0x1f;
+
+ /* disallow unsupported 10xxx op codes */
+ if (((op >> 3) & 0x3) == 2) {
+ pr_err("patch: unsupported opcode %08x\n", insn);
+ return -EINVAL;
+ }
+
+ /* disallow Rn == PC and Rd == PC */
+ if (((insn >> 16) & 0xf) == 0xf || ((insn >> 12) & 0xf) == 0xf) {
+ pr_err("patch: unsupported register %08x\n", insn);
+ return -EINVAL;
+ }
+
+ imm = *(u32 *)p->patch_data[0];
+
+ rot = imm ? __ffs(imm) / 2 : 0;
+ val = imm >> (rot * 2);
+ rot = (-rot) & 0xf;
+
+ /* does this fit in 8-bit? */
+ if (val > 0xff) {
+ pr_err("patch: constant overflow %08x\n", imm);
+ return -EINVAL;
+ }
+
+ /* patch in new immediate and rotation */
+ ninsn = (insn & ~0xfff) | (rot << 8) | val;
+
+ *insn_ptr = __opcode_to_mem_arm(ninsn);
+
+ return 0;
+}
+
+static int apply_patch_imm8_thumb(const struct patch_info *p)
+{
+ u32 insn, ninsn, op, *insn_ptr = p->insn_start;
+ u32 imm, rot, val;
+ int size = p->insn_end - p->insn_start;
+ const u32 supported_ops = (BIT(0) | /* and */
+ BIT(1) | /* bic */
+ BIT(2) | /* orr/mov */
+ BIT(3) | /* orn/mvn */
+ BIT(4) | /* eor */
+ BIT(8) | /* add */
+ BIT(10) | /* adc */
+ BIT(11) | /* sbc */
+ BIT(12) | /* sub */
+ BIT(13)); /* rsb */
+
+ if (size != 4) {
+ pr_err("patch: bad template size %d\n", size);
+ return -EINVAL;
+ }
+
+ insn = __mem_to_opcode_thumb32(p->patch_data[1]);
+ if (!__opcode_is_thumb32(insn)) {
+ pr_err("patch: invalid thumb2 insn %08x\n", insn);
+ return -EINVAL;
+ }
+
+ /* allow only data processing (immediate)
+ * 1111 0x0x xxx0 xxxx 0xxx xxxx xxxx xxxx */
+ if ((insn & 0xfa008000) != 0xf0000000) {
+ pr_err("patch: unknown insn %08x\n", insn);
+ return -EINVAL;
+ }
+
+ /* disallow Rn == PC and Rd == PC */
+ if (((insn >> 8) & 0xf) == 0xf || ((insn >> 16) & 0xf) == 0xf) {
+ pr_err("patch: unsupported register %08x\n", insn);
+ return -EINVAL;
+ }
+
+ /* extract op code */
+ op = (insn >> 21) & 0xf;
+
+ /* disallow unsupported opcodes */
+ if ((supported_ops & BIT(op)) == 0) {
+ pr_err("patch: unsupported opcode %x\n", op);
+ return -EINVAL;
+ }
+
+ imm = *(u32 *)p->patch_data[0];
+
+ if (imm <= 0xff) {
+ rot = 0;
+ val = imm;
+ } else {
+ rot = 32 - fls(imm); /* clz */
+ if (imm & ~(0xff000000 >> rot)) {
+ pr_err("patch: constant overflow %08x\n", imm);
+ return -EINVAL;
+ }
+ val = (imm >> (24 - rot)) & 0x7f;
+ rot += 8; /* encoded i:imm3:a */
+
+ /* pack least-sig rot bit into most-sig val bit */
+ val |= (rot & 1) << 7;
+ rot >>= 1;
+ }
+
+ ninsn = insn & ~(BIT(26) | 0x7 << 12 | 0xff);
+ ninsn |= (rot >> 3) << 26; /* field "i" */
+ ninsn |= (rot & 0x7) << 12; /* field "imm3" */
+ ninsn |= val;
+
+ *insn_ptr = __opcode_to_mem_thumb32(ninsn);
+
+ return 0;
+}
+
+int patch_kernel(const void *table, unsigned size)
+{
+ const struct patch_info *p = table, *end = (table + size);
+ bool thumb2 = IS_ENABLED(CONFIG_THUMB2_KERNEL);
+
+ for (p = table; p < end; p = patch_next(p)) {
+ int type = p->type & PATCH_TYPE_MASK;
+ int ret;
+
+ if (type == PATCH_IMM8) {
+ ret = (thumb2 ? apply_patch_imm8_thumb(p) :
+ apply_patch_imm8_arm(p));
+ } else {
+ pr_err("invalid patch type %d\n", type);
+ ret = -EINVAL;
+ }
+
+ if (ret < 0)
+ return ret;
+ }
+ return 0;
+}
+
+static void __init init_patch_kernel(void)
+{
+ const void *start = &__patch_table_begin;
+ const void *end = &__patch_table_end;
+
+ BUG_ON(patch_kernel(start, end - start));
+ flush_icache_range(init_mm.start_code, init_mm.end_code);
+}
+
void __init setup_arch(char **cmdline_p)
{
struct machine_desc *mdesc;
@@ -998,6 +1171,8 @@ void __init setup_arch(char **cmdline_p)

if (mdesc->init_early)
mdesc->init_early();
+
+ init_patch_kernel();
}


diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index 36ff15b..bacb275 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -167,6 +167,16 @@ SECTIONS
*(.pv_table)
__pv_table_end = .;
}
+ .init.patch_table : {
+ __patch_table_begin = .;
+ *(.patch.table)
+ __patch_table_end = .;
+ }
+ .init.patch_code : {
+ __patch_code_begin = .;
+ *(.patch.code)
+ __patch_code_end = .;
+ }
.init.data : {
#ifndef CONFIG_XIP_KERNEL
INIT_DATA
--
1.7.9.5


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