Message-ID: <50399556C9727B4D88A595C8584AAB37B4E49CAB@GSjpTKYDCembx32.service.hitachi.net>
Date:	Tue, 15 Mar 2016 04:28:03 +0000
From:	平松雅巳 / HIRAMATU，MASAMI 
	<masami.hiramatsu.pt@...achi.com>
To:	"'Zi Shen Lim'" <zlim.lnx@...il.com>,
	Will Deacon <will.deacon@....com>,
	Alexei Starovoitov <ast@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Catalin Marinas <catalin.marinas@....com>
CC:	Rabin Vincent <rabin@....in>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	sysp-manager <cti.systems-productivity-manager.ts@...achi.com>
Subject: RE: [PATCH 1/2] arm64: insn: remove BUG_ON from codegen

>
>During code generation, we used to BUG_ON unknown/unsupported encoding
>or invalid parameters.
>
>Instead, now we report these as errors and simply return the
>instruction AARCH64_BREAK_FAULT. Users of these codegen helpers should
>check for and handle this failure condition as appropriate.
>
>Otherwise, unhandled codegen failure will result in trapping at
>run-time due to AARCH64_BREAK_FAULT, which is arguably better than a
>BUG_ON.

Looks good to me.

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

Thanks,

>
>Signed-off-by: Zi Shen Lim <zlim.lnx@...il.com>
>Cc: Will Deacon <will.deacon@....com>
>---
>Per discussion here: http://www.spinics.net/lists/arm-kernel/msg474179.html
>
> arch/arm64/kernel/insn.c | 165 ++++++++++++++++++++++++++++++++---------------
> 1 file changed, 112 insertions(+), 53 deletions(-)
>
>diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
>index c08b9ad..7371455 100644
>--- a/arch/arm64/kernel/insn.c
>+++ b/arch/arm64/kernel/insn.c
>@@ -2,7 +2,7 @@
>  * Copyright (C) 2013 Huawei Ltd.
>  * Author: Jiang Liu <liuj97@...il.com>
>  *
>- * Copyright (C) 2014 Zi Shen Lim <zlim.lnx@...il.com>
>+ * Copyright (C) 2014-2016 Zi Shen Lim <zlim.lnx@...il.com>
>  *
>  * 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
>@@ -363,6 +363,9 @@ u32 __kprobes aarch64_insn_encode_immediate(enum aarch64_insn_imm_type type,
> 	u32 immlo, immhi, mask;
> 	int shift;
>
>+	if (insn == AARCH64_BREAK_FAULT)
>+		return AARCH64_BREAK_FAULT;
>+
> 	switch (type) {
> 	case AARCH64_INSN_IMM_ADR:
> 		shift = 0;
>@@ -377,7 +380,7 @@ u32 __kprobes aarch64_insn_encode_immediate(enum aarch64_insn_imm_type type,
> 		if (aarch64_get_imm_shift_mask(type, &mask, &shift) < 0) {
> 			pr_err("aarch64_insn_encode_immediate: unknown immediate encoding %d\n",
> 			       type);
>-			return 0;
>+			return AARCH64_BREAK_FAULT;
> 		}
> 	}
>
>@@ -394,9 +397,12 @@ static u32 aarch64_insn_encode_register(enum aarch64_insn_register_type type,
> {
> 	int shift;
>
>+	if (insn == AARCH64_BREAK_FAULT)
>+		return AARCH64_BREAK_FAULT;
>+
> 	if (reg < AARCH64_INSN_REG_0 || reg > AARCH64_INSN_REG_SP) {
> 		pr_err("%s: unknown register encoding %d\n", __func__, reg);
>-		return 0;
>+		return AARCH64_BREAK_FAULT;
> 	}
>
> 	switch (type) {
>@@ -417,7 +423,7 @@ static u32 aarch64_insn_encode_register(enum aarch64_insn_register_type type,
> 	default:
> 		pr_err("%s: unknown register type encoding %d\n", __func__,
> 		       type);
>-		return 0;
>+		return AARCH64_BREAK_FAULT;
> 	}
>
> 	insn &= ~(GENMASK(4, 0) << shift);
>@@ -446,7 +452,7 @@ static u32 aarch64_insn_encode_ldst_size(enum aarch64_insn_size_type type,
> 		break;
> 	default:
> 		pr_err("%s: unknown size encoding %d\n", __func__, type);
>-		return 0;
>+		return AARCH64_BREAK_FAULT;
> 	}
>
> 	insn &= ~GENMASK(31, 30);
>@@ -460,14 +466,17 @@ static inline long branch_imm_common(unsigned long pc, unsigned long addr,
> {
> 	long offset;
>
>-	/*
>-	 * PC: A 64-bit Program Counter holding the address of the current
>-	 * instruction. A64 instructions must be word-aligned.
>-	 */
>-	BUG_ON((pc & 0x3) || (addr & 0x3));
>+	if ((pc & 0x3) || (addr & 0x3)) {
>+		pr_err("%s: A64 instructions must be word aligned\n", __func__);
>+		return range;
>+	}
>
> 	offset = ((long)addr - (long)pc);
>-	BUG_ON(offset < -range || offset >= range);
>+
>+	if (offset < -range || offset >= range) {
>+		pr_err("%s: offset out of range\n", __func__);
>+		return range;
>+	}
>
> 	return offset;
> }
>@@ -484,6 +493,8 @@ u32 __kprobes aarch64_insn_gen_branch_imm(unsigned long pc, unsigned long addr,
> 	 * texts are within +/-128M.
> 	 */
> 	offset = branch_imm_common(pc, addr, SZ_128M);
>+	if (offset >= SZ_128M)
>+		return AARCH64_BREAK_FAULT;
>
> 	switch (type) {
> 	case AARCH64_INSN_BRANCH_LINK:
>@@ -493,7 +504,7 @@ u32 __kprobes aarch64_insn_gen_branch_imm(unsigned long pc, unsigned long addr,
> 		insn = aarch64_insn_get_b_value();
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown branch encoding %d\n", __func__, type);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>@@ -510,6 +521,8 @@ u32 aarch64_insn_gen_comp_branch_imm(unsigned long pc, unsigned long addr,
> 	long offset;
>
> 	offset = branch_imm_common(pc, addr, SZ_1M);
>+	if (offset >= SZ_1M)
>+		return AARCH64_BREAK_FAULT;
>
> 	switch (type) {
> 	case AARCH64_INSN_BRANCH_COMP_ZERO:
>@@ -519,7 +532,7 @@ u32 aarch64_insn_gen_comp_branch_imm(unsigned long pc, unsigned long addr,
> 		insn = aarch64_insn_get_cbnz_value();
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown branch encoding %d\n", __func__, type);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>@@ -530,7 +543,7 @@ u32 aarch64_insn_gen_comp_branch_imm(unsigned long pc, unsigned long addr,
> 		insn |= AARCH64_INSN_SF_BIT;
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown variant encoding %d\n", __func__, variant);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>@@ -550,7 +563,10 @@ u32 aarch64_insn_gen_cond_branch_imm(unsigned long pc, unsigned long addr,
>
> 	insn = aarch64_insn_get_bcond_value();
>
>-	BUG_ON(cond < AARCH64_INSN_COND_EQ || cond > AARCH64_INSN_COND_AL);
>+	if (cond < AARCH64_INSN_COND_EQ || cond > AARCH64_INSN_COND_AL) {
>+		pr_err("%s: unknown condition encoding %d\n", __func__, cond);
>+		return AARCH64_BREAK_FAULT;
>+	}
> 	insn |= cond;
>
> 	return aarch64_insn_encode_immediate(AARCH64_INSN_IMM_19, insn,
>@@ -583,7 +599,7 @@ u32 aarch64_insn_gen_branch_reg(enum aarch64_insn_register reg,
> 		insn = aarch64_insn_get_ret_value();
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown branch encoding %d\n", __func__, type);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>@@ -606,7 +622,7 @@ u32 aarch64_insn_gen_load_store_reg(enum aarch64_insn_register reg,
> 		insn = aarch64_insn_get_str_reg_value();
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown load/store encoding %d\n", __func__, type);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>@@ -645,26 +661,30 @@ u32 aarch64_insn_gen_load_store_pair(enum aarch64_insn_register reg1,
> 		insn = aarch64_insn_get_stp_post_value();
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown load/store encoding %d\n", __func__, type);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
> 	switch (variant) {
> 	case AARCH64_INSN_VARIANT_32BIT:
>-		/* offset must be multiples of 4 in the range [-256, 252] */
>-		BUG_ON(offset & 0x3);
>-		BUG_ON(offset < -256 || offset > 252);
>+		if ((offset & 0x3) || (offset < -256) || (offset > 252)) {
>+			pr_err("%s: offset must be multiples of 4 in the range of [-256, 252] %d\n",
>+			       __func__, offset);
>+			return AARCH64_BREAK_FAULT;
>+		}
> 		shift = 2;
> 		break;
> 	case AARCH64_INSN_VARIANT_64BIT:
>-		/* offset must be multiples of 8 in the range [-512, 504] */
>-		BUG_ON(offset & 0x7);
>-		BUG_ON(offset < -512 || offset > 504);
>+		if ((offset & 0x7) || (offset < -512) || (offset > 504)) {
>+			pr_err("%s: offset must be multiples of 8 in the range of [-512, 504] %d\n",
>+			       __func__, offset);
>+			return AARCH64_BREAK_FAULT;
>+		}
> 		shift = 3;
> 		insn |= AARCH64_INSN_SF_BIT;
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown variant encoding %d\n", __func__, variant);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>@@ -702,7 +722,7 @@ u32 aarch64_insn_gen_add_sub_imm(enum aarch64_insn_register dst,
> 		insn = aarch64_insn_get_subs_imm_value();
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown add/sub encoding %d\n", __func__, type);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>@@ -713,11 +733,14 @@ u32 aarch64_insn_gen_add_sub_imm(enum aarch64_insn_register dst,
> 		insn |= AARCH64_INSN_SF_BIT;
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown variant encoding %d\n", __func__, variant);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>-	BUG_ON(imm & ~(SZ_4K - 1));
>+	if (imm & ~(SZ_4K - 1)) {
>+		pr_err("%s: invalid immediate encoding %d\n", __func__, imm);
>+		return AARCH64_BREAK_FAULT;
>+	}
>
> 	insn = aarch64_insn_encode_register(AARCH64_INSN_REGTYPE_RD, insn, dst);
>
>@@ -746,7 +769,7 @@ u32 aarch64_insn_gen_bitfield(enum aarch64_insn_register dst,
> 		insn = aarch64_insn_get_sbfm_value();
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown bitfield encoding %d\n", __func__, type);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>@@ -759,12 +782,18 @@ u32 aarch64_insn_gen_bitfield(enum aarch64_insn_register dst,
> 		mask = GENMASK(5, 0);
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown variant encoding %d\n", __func__, variant);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>-	BUG_ON(immr & ~mask);
>-	BUG_ON(imms & ~mask);
>+	if (immr & ~mask) {
>+		pr_err("%s: invalid immr encoding %d\n", __func__, immr);
>+		return AARCH64_BREAK_FAULT;
>+	}
>+	if (imms & ~mask) {
>+		pr_err("%s: invalid imms encoding %d\n", __func__, imms);
>+		return AARCH64_BREAK_FAULT;
>+	}
>
> 	insn = aarch64_insn_encode_register(AARCH64_INSN_REGTYPE_RD, insn, dst);
>
>@@ -793,23 +822,33 @@ u32 aarch64_insn_gen_movewide(enum aarch64_insn_register dst,
> 		insn = aarch64_insn_get_movn_value();
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown movewide encoding %d\n", __func__, type);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>-	BUG_ON(imm & ~(SZ_64K - 1));
>+	if (imm & ~(SZ_64K - 1)) {
>+		pr_err("%s: invalid immediate encoding %d\n", __func__, imm);
>+		return AARCH64_BREAK_FAULT;
>+	}
>
> 	switch (variant) {
> 	case AARCH64_INSN_VARIANT_32BIT:
>-		BUG_ON(shift != 0 && shift != 16);
>+		if (shift != 0 && shift != 16) {
>+			pr_err("%s: invalid shift encoding %d\n", __func__,
>+			       shift);
>+			return AARCH64_BREAK_FAULT;
>+		}
> 		break;
> 	case AARCH64_INSN_VARIANT_64BIT:
> 		insn |= AARCH64_INSN_SF_BIT;
>-		BUG_ON(shift != 0 && shift != 16 && shift != 32 &&
>-		       shift != 48);
>+		if (shift != 0 && shift != 16 && shift != 32 && shift != 48) {
>+			pr_err("%s: invalid shift encoding %d\n", __func__,
>+			       shift);
>+			return AARCH64_BREAK_FAULT;
>+		}
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown variant encoding %d\n", __func__, variant);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>@@ -843,20 +882,28 @@ u32 aarch64_insn_gen_add_sub_shifted_reg(enum aarch64_insn_register dst,
> 		insn = aarch64_insn_get_subs_value();
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown add/sub encoding %d\n", __func__, type);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
> 	switch (variant) {
> 	case AARCH64_INSN_VARIANT_32BIT:
>-		BUG_ON(shift & ~(SZ_32 - 1));
>+		if (shift & ~(SZ_32 - 1)) {
>+			pr_err("%s: invalid shift encoding %d\n", __func__,
>+			       shift);
>+			return AARCH64_BREAK_FAULT;
>+		}
> 		break;
> 	case AARCH64_INSN_VARIANT_64BIT:
> 		insn |= AARCH64_INSN_SF_BIT;
>-		BUG_ON(shift & ~(SZ_64 - 1));
>+		if (shift & ~(SZ_64 - 1)) {
>+			pr_err("%s: invalid shift encoding %d\n", __func__,
>+			       shift);
>+			return AARCH64_BREAK_FAULT;
>+		}
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown variant encoding %d\n", __func__, variant);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>@@ -885,11 +932,15 @@ u32 aarch64_insn_gen_data1(enum aarch64_insn_register dst,
> 		insn = aarch64_insn_get_rev32_value();
> 		break;
> 	case AARCH64_INSN_DATA1_REVERSE_64:
>-		BUG_ON(variant != AARCH64_INSN_VARIANT_64BIT);
>+		if (variant != AARCH64_INSN_VARIANT_64BIT) {
>+			pr_err("%s: invalid variant for reverse64 %d\n",
>+			       __func__, variant);
>+			return AARCH64_BREAK_FAULT;
>+		}
> 		insn = aarch64_insn_get_rev64_value();
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown data1 encoding %d\n", __func__, type);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>@@ -900,7 +951,7 @@ u32 aarch64_insn_gen_data1(enum aarch64_insn_register dst,
> 		insn |= AARCH64_INSN_SF_BIT;
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown variant encoding %d\n", __func__, variant);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>@@ -937,7 +988,7 @@ u32 aarch64_insn_gen_data2(enum aarch64_insn_register dst,
> 		insn = aarch64_insn_get_rorv_value();
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown data2 encoding %d\n", __func__, type);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>@@ -948,7 +999,7 @@ u32 aarch64_insn_gen_data2(enum aarch64_insn_register dst,
> 		insn |= AARCH64_INSN_SF_BIT;
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown variant encoding %d\n", __func__, variant);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>@@ -976,7 +1027,7 @@ u32 aarch64_insn_gen_data3(enum aarch64_insn_register dst,
> 		insn = aarch64_insn_get_msub_value();
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown data3 encoding %d\n", __func__, type);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>@@ -987,7 +1038,7 @@ u32 aarch64_insn_gen_data3(enum aarch64_insn_register dst,
> 		insn |= AARCH64_INSN_SF_BIT;
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown variant encoding %d\n", __func__, variant);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>@@ -1037,20 +1088,28 @@ u32 aarch64_insn_gen_logical_shifted_reg(enum aarch64_insn_register dst,
> 		insn = aarch64_insn_get_bics_value();
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown logical encoding %d\n", __func__, type);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
> 	switch (variant) {
> 	case AARCH64_INSN_VARIANT_32BIT:
>-		BUG_ON(shift & ~(SZ_32 - 1));
>+		if (shift & ~(SZ_32 - 1)) {
>+			pr_err("%s: invalid shift encoding %d\n", __func__,
>+			       shift);
>+			return AARCH64_BREAK_FAULT;
>+		}
> 		break;
> 	case AARCH64_INSN_VARIANT_64BIT:
> 		insn |= AARCH64_INSN_SF_BIT;
>-		BUG_ON(shift & ~(SZ_64 - 1));
>+		if (shift & ~(SZ_64 - 1)) {
>+			pr_err("%s: invalid shift encoding %d\n", __func__,
>+			       shift);
>+			return AARCH64_BREAK_FAULT;
>+		}
> 		break;
> 	default:
>-		BUG_ON(1);
>+		pr_err("%s: unknown variant encoding %d\n", __func__, variant);
> 		return AARCH64_BREAK_FAULT;
> 	}
>
>--
>1.9.1
>
>
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>linux-arm-kernel@...ts.infradead.org
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