From 5ccd8e5133a43e574be8d66aae3a230c39b4b67a Mon Sep 17 00:00:00 2001
From: Keith Randall <khr@golang.org>
Date: Thu, 10 Mar 2022 15:26:22 -0800
Subject: [PATCH] internal/cpu: disallow disabling options that are required
 for microarch
MIME-Version: 1.0
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e.g., if GOAMD64=v3, don't allow GODEBUG=cpu.XXX=off for XXX which
are required for v3.

Change-Id: Ib58a4c8b13c5464ba476448ba44bbb261218787c
Reviewed-on: https://go-review.googlesource.com/c/go/+/391694
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Martin Möhrmann <martin@golang.org>
---
 src/internal/cpu/cpu_x86.go | 34 ++++++++++++++++++++++++----------
 src/internal/cpu/cpu_x86.s  | 17 +++++++++++++++++
 2 files changed, 41 insertions(+), 10 deletions(-)

diff --git a/src/internal/cpu/cpu_x86.go b/src/internal/cpu/cpu_x86.go
index 81d5ceed61..6fd979a747 100644
--- a/src/internal/cpu/cpu_x86.go
+++ b/src/internal/cpu/cpu_x86.go
@@ -14,6 +14,9 @@ func cpuid(eaxArg, ecxArg uint32) (eax, ebx, ecx, edx uint32)
 // xgetbv with ecx = 0 is implemented in cpu_x86.s.
 func xgetbv() (eax, edx uint32)
 
+// getGOAMD64level is implemented in cpu_x86.s. Returns number in [1,4].
+func getGOAMD64level() int32
+
 const (
 	// edx bits
 	cpuid_SSE2 = 1 << 26
@@ -47,19 +50,30 @@ func doinit() {
 	options = []option{
 		{Name: "adx", Feature: &X86.HasADX},
 		{Name: "aes", Feature: &X86.HasAES},
-		{Name: "avx", Feature: &X86.HasAVX},
-		{Name: "avx2", Feature: &X86.HasAVX2},
-		{Name: "bmi1", Feature: &X86.HasBMI1},
-		{Name: "bmi2", Feature: &X86.HasBMI2},
 		{Name: "erms", Feature: &X86.HasERMS},
-		{Name: "fma", Feature: &X86.HasFMA},
 		{Name: "pclmulqdq", Feature: &X86.HasPCLMULQDQ},
-		{Name: "popcnt", Feature: &X86.HasPOPCNT},
 		{Name: "rdtscp", Feature: &X86.HasRDTSCP},
-		{Name: "sse3", Feature: &X86.HasSSE3},
-		{Name: "sse41", Feature: &X86.HasSSE41},
-		{Name: "sse42", Feature: &X86.HasSSE42},
-		{Name: "ssse3", Feature: &X86.HasSSSE3},
+	}
+	level := getGOAMD64level()
+	if level < 2 {
+		// These options are required at level 2. At lower levels
+		// they can be turned off.
+		options = append(options,
+			option{Name: "popcnt", Feature: &X86.HasPOPCNT},
+			option{Name: "sse3", Feature: &X86.HasSSE3},
+			option{Name: "sse41", Feature: &X86.HasSSE41},
+			option{Name: "sse42", Feature: &X86.HasSSE42},
+			option{Name: "ssse3", Feature: &X86.HasSSSE3})
+	}
+	if level < 3 {
+		// These options are required at level 3. At lower levels
+		// they can be turned off.
+		options = append(options,
+			option{Name: "avx", Feature: &X86.HasAVX},
+			option{Name: "avx2", Feature: &X86.HasAVX2},
+			option{Name: "bmi1", Feature: &X86.HasBMI1},
+			option{Name: "bmi2", Feature: &X86.HasBMI2},
+			option{Name: "fma", Feature: &X86.HasFMA})
 	}
 
 	maxID, _, _, _ := cpuid(0, 0)
diff --git a/src/internal/cpu/cpu_x86.s b/src/internal/cpu/cpu_x86.s
index edef21905c..2ee8eca248 100644
--- a/src/internal/cpu/cpu_x86.s
+++ b/src/internal/cpu/cpu_x86.s
@@ -24,3 +24,20 @@ TEXT ·xgetbv(SB),NOSPLIT,$0-8
 	MOVL AX, eax+0(FP)
 	MOVL DX, edx+4(FP)
 	RET
+
+// func getGOAMD64level() int32
+TEXT ·getGOAMD64level(SB),NOSPLIT,$0-4
+#ifdef GOAMD64_v4
+	MOVL $4, ret+0(FP)
+#else
+#ifdef GOAMD64_v3
+	MOVL $3, ret+0(FP)
+#else
+#ifdef GOAMD64_v2
+	MOVL $2, ret+0(FP)
+#else
+	MOVL $1, ret+0(FP)
+#endif
+#endif
+#endif
+	RET
-- 
2.50.0