[go] internal/cpu: disallow disabling options that are required for microarch

Keith Randall (Gerrit)

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Mar 10, 2022, 6:27:46 PM3/10/22

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Keith Randall would like Martin Möhrmann to review this change.

internal/cpu: disallow disabling options that are required for microarch

e.g., if GOAMD64=v3, don't allow GODEBUG=cpu.XXX=off for XXX which
are required for v3.

Change-Id: Ib58a4c8b13c5464ba476448ba44bbb261218787c
---
M src/internal/cpu/cpu_x86.go
M src/internal/cpu/cpu_x86.s
2 files changed, 53 insertions(+), 10 deletions(-)

diff --git a/src/internal/cpu/cpu_x86.go b/src/internal/cpu/cpu_x86.go
index 81d5cee..6fd979a 100644
--- a/src/internal/cpu/cpu_x86.go
+++ b/src/internal/cpu/cpu_x86.go
@@ -14,6 +14,9 @@
 // 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 @@
 	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 edef219..2ee8eca 100644
--- a/src/internal/cpu/cpu_x86.s
+++ b/src/internal/cpu/cpu_x86.s
@@ -24,3 +24,20 @@
 	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

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Keith Randall (Gerrit)

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Mar 10, 2022, 6:29:57 PM3/10/22

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1 comment:

Patchset:
- Patch Set #1:
  This CL will lead to getting "unknown cpu feature" for features that are required and you're trying to modify. But this is kind of a specialized feature anyway, I don't think that's a big downside.
  We'd also need a similar change to x/sys, I guess?

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Martin Möhrmann (Gerrit)

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Mar 14, 2022, 5:06:51 PM3/14/22

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Patch set 1:Code-Review +2

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Keith Randall (Gerrit)

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Mar 14, 2022, 5:23:41 PM3/14/22

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Keith Randall submitted this change.

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Approvals:
  Martin Möhrmann: Looks good to me, approved
  Keith Randall: Trusted; Run TryBots
  Gopher Robot: TryBots succeeded

internal/cpu: disallow disabling options that are required for microarch

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 <k...@golang.org>
Run-TryBot: Keith Randall <k...@golang.org>
TryBot-Result: Gopher Robot <go...@golang.org>
Reviewed-by: Martin Möhrmann <mar...@golang.org>


---
M src/internal/cpu/cpu_x86.go
M src/internal/cpu/cpu_x86.s

2 files changed, 58 insertions(+), 10 deletions(-)

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Tobias Klauser (Gerrit)

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Mar 15, 2022, 4:20:37 AM3/15/22

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1 comment:

Patchset:
- Patch Set #2:
  This change seems to break TestDisableSSE3 on the linux-amd64-goamd64v3 builder:
```
 --- FAIL: TestDisableSSE3 (0.00s)
     cpu_test.go:44: TestSSE3DebugOption with GODEBUG=cpu.sse3=off: want PASS, got FAIL
```
  https://build.golang.org/log/c8a96c3fcbf4cc423450989d9f458b20f32d0d07

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