runtime/internal/syscall, syscall: replace RawSyscall6 with runtime implementation on linux

For #51087

Change-Id: I75a1bdeb5089454595f5ca04765a9c6e45cf9bd5
Reviewed-on: https://go-review.googlesource.com/c/go/+/388475
Run-TryBot: Michael Pratt <mpratt@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 27 insertions, 0 deletions

diff --git a/src/runtime/internal/syscall/syscall_linux.go b/src/runtime/internal/syscall/syscall_linux.go
index 06d5f21e7c..7f268e8fba 100644
--- a/src/runtime/internal/syscall/syscall_linux.go
+++ b/src/runtime/internal/syscall/syscall_linux.go
@@ -5,8 +5,35 @@
 // Package syscall provides the syscall primitives required for the runtime.
 package syscall
 
+import (
+	_ "unsafe" // for go:linkname
+)
+
 // TODO(https://go.dev/issue/51087): This package is incomplete and currently
 // only contains very minimal support for Linux.
 
 // Syscall6 calls system call number 'num' with arguments a1-6.
 func Syscall6(num, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, errno uintptr)
+
+// syscall_RawSyscall6 is a push linkname to export Syscall6 as
+// syscall.RawSyscall6.
+//
+// //go:uintptrkeepalive because the uintptr argument may be converted pointers
+// that need to be kept alive in the caller (this is implied for Syscall6 since
+// it has no body).
+//
+// //go:nosplit because stack copying does not account for uintptrkeepalive, so
+// the stack must not grow. Stack copying cannot blindly assume that all
+// uintptr arguments are pointers, because some values may look like pointers,
+// but not really be pointers, and adjusting their value would break the call.
+//
+// This is a separate wrapper because we can't export one function as two
+// names. The assembly implementations name themselves Syscall6 would not be
+// affected by a linkname.
+//
+//go:uintptrkeepalive
+//go:nosplit
+//go:linkname syscall_RawSyscall6 syscall.RawSyscall6
+func syscall_RawSyscall6(num, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, errno uintptr) {
+	return Syscall6(num, a1, a2, a3, a4, a5, a6)
+}