syscall: fix vet complaints for all dragonfly, freebsd, netbsd, openbsd

Working toward making the tree vet-safe instead of having
so many exceptions in cmd/vet/all/whitelist.

This CL makes "go vet -unsafeptr=false runtime" happy for these GOOSes,
while keeping "GO_BUILDER_NAME=misc-vetall go tool dist test" happy too.

For #31916.

Change-Id: Id2e1223497bd0cd6e880cd81f3ece6363e58219f
Reviewed-on: https://go-review.googlesource.com/c/go/+/176104
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

src/cmd/vet/all/whitelist/dragonfly_amd64.txt

-// dragonfly/amd64-specific vet whitelist. See readme.txt for details.
-
-
-syscall/asm9_unix2_amd64.s: [amd64] Syscall9: 8(SP) should be num+0(FP)
-syscall/asm9_unix2_amd64.s: [amd64] Syscall9: 16(SP) should be a1+8(FP)
-syscall/asm9_unix2_amd64.s: [amd64] Syscall9: 24(SP) should be a2+16(FP)

src/cmd/vet/all/whitelist/freebsd_386.txt

@@ -6,13 +6,3 @@ runtime/sys_freebsd_386.s: [386] sigtramp: unknown variable info
 runtime/sys_freebsd_386.s: [386] sigtramp: unknown variable context
 runtime/sys_freebsd_386.s: [386] sigtramp: unknown variable context
 runtime/sys_freebsd_386.s: [386] i386_set_ldt: function i386_set_ldt missing Go declaration
-syscall/asm_unix_386.s: [386] Syscall: 8(SP) should be a1+4(FP)
-syscall/asm_unix_386.s: [386] Syscall: 4(SP) should be trap+0(FP)
-syscall/asm_unix_386.s: [386] Syscall6: 8(SP) should be a1+4(FP)
-syscall/asm_unix_386.s: [386] Syscall6: 4(SP) should be trap+0(FP)
-syscall/asm_unix_386.s: [386] Syscall9: 8(SP) should be a1+4(FP)
-syscall/asm_unix_386.s: [386] Syscall9: 4(SP) should be num+0(FP)
-syscall/asm_unix_386.s: [386] RawSyscall: 8(SP) should be a1+4(FP)
-syscall/asm_unix_386.s: [386] RawSyscall: 4(SP) should be trap+0(FP)
-syscall/asm_unix_386.s: [386] RawSyscall6: 8(SP) should be a1+4(FP)
-syscall/asm_unix_386.s: [386] RawSyscall6: 4(SP) should be trap+0(FP)

src/cmd/vet/all/whitelist/freebsd_amd64.txt

-// freebsd/amd64-specific vet whitelist. See readme.txt for details.
-
-syscall/asm9_unix2_amd64.s: [amd64] Syscall9: 8(SP) should be num+0(FP)
-syscall/asm9_unix2_amd64.s: [amd64] Syscall9: 16(SP) should be a1+8(FP)
-syscall/asm9_unix2_amd64.s: [amd64] Syscall9: 24(SP) should be a2+16(FP)

src/cmd/vet/all/whitelist/netbsd_386.txt

@@ -7,13 +7,3 @@ runtime/sys_netbsd_386.s: [386] sigtramp: unknown variable signo
 runtime/sys_netbsd_386.s: [386] sigtramp: unknown variable info
 runtime/sys_netbsd_386.s: [386] sigtramp: unknown variable context
 
-syscall/asm_unix_386.s: [386] Syscall: 8(SP) should be a1+4(FP)
-syscall/asm_unix_386.s: [386] Syscall: 4(SP) should be trap+0(FP)
-syscall/asm_unix_386.s: [386] Syscall6: 8(SP) should be a1+4(FP)
-syscall/asm_unix_386.s: [386] Syscall6: 4(SP) should be trap+0(FP)
-syscall/asm_unix_386.s: [386] Syscall9: 8(SP) should be a1+4(FP)
-syscall/asm_unix_386.s: [386] Syscall9: 4(SP) should be num+0(FP)
-syscall/asm_unix_386.s: [386] RawSyscall: 8(SP) should be a1+4(FP)
-syscall/asm_unix_386.s: [386] RawSyscall: 4(SP) should be trap+0(FP)
-syscall/asm_unix_386.s: [386] RawSyscall6: 8(SP) should be a1+4(FP)
-syscall/asm_unix_386.s: [386] RawSyscall6: 4(SP) should be trap+0(FP)

src/cmd/vet/all/whitelist/netbsd_arm.txt

-// netbsd/arm-specific vet whitelist. See readme.txt for details.
-
-syscall/asm_netbsd_arm.s: [arm] Syscall9: unknown variable trap; offset 0 is num+0(FP)

src/cmd/vet/all/whitelist/openbsd_386.txt

@@ -3,13 +3,3 @@
 runtime/sys_openbsd_386.s: [386] sigtramp: unknown variable signo
 runtime/sys_openbsd_386.s: [386] sigtramp: unknown variable info
 runtime/sys_openbsd_386.s: [386] sigtramp: unknown variable context
-syscall/asm_unix_386.s: [386] Syscall: 8(SP) should be a1+4(FP)
-syscall/asm_unix_386.s: [386] Syscall: 4(SP) should be trap+0(FP)
-syscall/asm_unix_386.s: [386] Syscall6: 8(SP) should be a1+4(FP)
-syscall/asm_unix_386.s: [386] Syscall6: 4(SP) should be trap+0(FP)
-syscall/asm_unix_386.s: [386] Syscall9: 8(SP) should be a1+4(FP)
-syscall/asm_unix_386.s: [386] Syscall9: 4(SP) should be num+0(FP)
-syscall/asm_unix_386.s: [386] RawSyscall: 8(SP) should be a1+4(FP)
-syscall/asm_unix_386.s: [386] RawSyscall: 4(SP) should be trap+0(FP)
-syscall/asm_unix_386.s: [386] RawSyscall6: 8(SP) should be a1+4(FP)
-syscall/asm_unix_386.s: [386] RawSyscall6: 4(SP) should be trap+0(FP)

src/syscall/asm9_unix2_amd64.s

@@ -24,12 +24,14 @@ TEXT	·Syscall9(SB),NOSPLIT,$0-104
 
 	// shift around the last three arguments so they're at the
 	// top of the stack when the syscall is called.
+	// note that we are scribbling over the Go arguments now.
+	MOVQ	SP, CX	// hide (SP) writes from vet
 	MOVQ	a7+56(FP), R11 // arg 7
-	MOVQ	R11, 8(SP)
+	MOVQ	R11, 8(CX)
 	MOVQ	a8+64(FP), R11 // arg 8
-	MOVQ	R11, 16(SP)
+	MOVQ	R11, 16(CX)
 	MOVQ	a9+72(FP), R11 // arg 9
-	MOVQ	R11, 24(SP)
+	MOVQ	R11, 24(CX)
 
 	SYSCALL
 	JCC	ok9

src/syscall/asm_netbsd_arm.s

@@ -62,7 +62,7 @@ error6:
 
 TEXT	·Syscall9(SB),NOSPLIT,$0-52
 	BL runtime·entersyscall(SB)
-	MOVW trap+0(FP), R0 // sigcall num
+	MOVW num+0(FP), R0 // sigcall num
 	MOVW a1+4(FP), R1 // a1
 	MOVW a2+8(FP), R2 // a2
 	MOVW a3+12(FP), R3 // a3

src/syscall/asm_unix_386.s

@@ -19,8 +19,8 @@ TEXT	·Syscall(SB),NOSPLIT,$0-28
 	CALL	runtime·entersyscall(SB)
 	MOVL	trap+0(FP), AX	// syscall entry
 	// slide args down on top of system call number
-	LEAL		8(SP), SI
-	LEAL		4(SP), DI
+	LEAL		a1+4(FP), SI
+	LEAL		trap+0(FP), DI
 	CLD
 	MOVSL
 	MOVSL
@@ -43,8 +43,8 @@ TEXT	·Syscall6(SB),NOSPLIT,$0-40
 	CALL	runtime·entersyscall(SB)
 	MOVL	trap+0(FP), AX	// syscall entry
 	// slide args down on top of system call number
-	LEAL		8(SP), SI
-	LEAL		4(SP), DI
+	LEAL		a1+4(FP), SI
+	LEAL		trap+0(FP), DI
 	CLD
 	MOVSL
 	MOVSL
@@ -70,8 +70,8 @@ TEXT	·Syscall9(SB),NOSPLIT,$0-52
 	CALL	runtime·entersyscall(SB)
 	MOVL	num+0(FP), AX	// syscall entry
 	// slide args down on top of system call number
-	LEAL		8(SP), SI
-	LEAL		4(SP), DI
+	LEAL		a1+4(FP), SI
+	LEAL		num+0(FP), DI
 	CLD
 	MOVSL
 	MOVSL
@@ -99,8 +99,8 @@ ok9:
 TEXT ·RawSyscall(SB),NOSPLIT,$0-28
 	MOVL	trap+0(FP), AX	// syscall entry
 	// slide args down on top of system call number
-	LEAL		8(SP), SI
-	LEAL		4(SP), DI
+	LEAL		a1+4(FP), SI
+	LEAL		trap+0(FP), DI
 	CLD
 	MOVSL
 	MOVSL
@@ -120,8 +120,8 @@ ok1:
 TEXT	·RawSyscall6(SB),NOSPLIT,$0-40
 	MOVL	trap+0(FP), AX	// syscall entry
 	// slide args down on top of system call number
-	LEAL		8(SP), SI
-	LEAL		4(SP), DI
+	LEAL		a1+4(FP), SI
+	LEAL		trap+0(FP), DI
 	CLD
 	MOVSL
 	MOVSL