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-rw-r--r--src/runtime/cgo/gcc_amd64.S55
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diff --git a/src/runtime/cgo/gcc_amd64.S b/src/runtime/cgo/gcc_amd64.S
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+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+.file "gcc_amd64.S"
+
+/*
+ * Apple still insists on underscore prefixes for C function names.
+ */
+#if defined(__APPLE__)
+#define EXT(s) _##s
+#else
+#define EXT(s) s
+#endif
+
+/*
+ * void crosscall_amd64(void (*fn)(void), void (*setg_gcc)(void*), void *g)
+ *
+ * Calling into the 6c tool chain, where all registers are caller save.
+ * Called from standard x86-64 ABI, where %rbx, %rbp, %r12-%r15
+ * are callee-save so they must be saved explicitly.
+ * The standard x86-64 ABI passes the three arguments m, g, fn
+ * in %rdi, %rsi, %rdx.
+ */
+.globl EXT(crosscall_amd64)
+EXT(crosscall_amd64):
+ pushq %rbx
+ pushq %rbp
+ pushq %r12
+ pushq %r13
+ pushq %r14
+ pushq %r15
+
+#if defined(_WIN64)
+ movq %r8, %rdi /* arg of setg_gcc */
+ call *%rdx /* setg_gcc */
+ call *%rcx /* fn */
+#else
+ movq %rdi, %rbx
+ movq %rdx, %rdi /* arg of setg_gcc */
+ call *%rsi /* setg_gcc */
+ call *%rbx /* fn */
+#endif
+
+ popq %r15
+ popq %r14
+ popq %r13
+ popq %r12
+ popq %rbp
+ popq %rbx
+ ret
+
+#ifdef __ELF__
+.section .note.GNU-stack,"",@progbits
+#endif