internal/fakecgo: remove clang mmap bug workaround (#432)

The workaround for clang's mmap is not necessary because fakecgo is not built
with clang. Anyway, I just removed that code from runtine/cgo, clang 3.8 was
shipped ten years ago. See https://go-review.googlesource.com/c/go/+/745662.

commit: 5110604b3385278be6887d0feead513a1bfe7a82
author: Quim Muntal · 7mo ago · 2026-03-05 13:19 UTC
committer: GitHub · 7mo ago · 2026-03-05 13:19 UTC
parent: 6e7b934
signature: GPG UnverifiedB5690EEEBB952194 The key is unknown

3 files · +12 -75

M internal/fakecgo/go_freebsd.go +4 -25


@@ -67,34 +67,13 @@ var setg_func uintptr
67	67		//go:nosplit
68	68		func x_cgo_init(g *G, setg uintptr) {
69	69		var size size_t
70		-	var attr *pthread_attr_t
71		-
72		-	/* The memory sanitizer distributed with versions of clang
73		-	before 3.8 has a bug: if you call mmap before malloc, mmap
74		-	may return an address that is later overwritten by the msan
75		-	library. Avoid this problem by forcing a call to malloc
76		-	here, before we ever call malloc.
77		-
78		-	This is only required for the memory sanitizer, so it's
79		-	unfortunate that we always run it. It should be possible
80		-	to remove this when we no longer care about versions of
81		-	clang before 3.8. The test for this is
82		-	misc/cgo/testsanitizers.
83		-
84		-	GCC works hard to eliminate a seemingly unnecessary call to
85		-	malloc, so we actually use the memory we allocate. */
	70	+	var attr pthread_attr_t
86	71
87	72		setg_func = setg
88		-	attr = (pthread_attr_t)(malloc(unsafe.Sizeof(attr)))
89		-	if attr == nil {
90		-	println("fakecgo: malloc failed")
91		-	abort()
92		-	}
93		-	pthread_attr_init(attr)
94		-	pthread_attr_getstacksize(attr, &size)
	73	+	pthread_attr_init(&attr)
	74	+	pthread_attr_getstacksize(&attr, &size)
95	75		// runtime/cgo uses __builtin_frame_address(0) instead of `uintptr(unsafe.Pointer(&size))`
96	76		// but this should be OK since we are taking the address of the first variable in this function.
97	77		g.stacklo = uintptr(unsafe.Pointer(&size)) - uintptr(size) + 4096
98		-	pthread_attr_destroy(attr)
99		-	free(unsafe.Pointer(attr))
	78	+	pthread_attr_destroy(&attr)
100	79		}


@@ -67,34 +67,13 @@ var setg_func uintptr
67		//go:nosplit	67		//go:nosplit
68		func x_cgo_init(g *G, setg uintptr) {	68		func x_cgo_init(g *G, setg uintptr) {
69		var size size_t	69		var size size_t
70	-	var attr *pthread_attr_t	70	+	var attr pthread_attr_t
71	-
72	-	/* The memory sanitizer distributed with versions of clang
73	-	before 3.8 has a bug: if you call mmap before malloc, mmap
74	-	may return an address that is later overwritten by the msan
75	-	library. Avoid this problem by forcing a call to malloc
76	-	here, before we ever call malloc.
77	-
78	-	This is only required for the memory sanitizer, so it's
79	-	unfortunate that we always run it. It should be possible
80	-	to remove this when we no longer care about versions of
81	-	clang before 3.8. The test for this is
82	-	misc/cgo/testsanitizers.
83	-
84	-	GCC works hard to eliminate a seemingly unnecessary call to
85	-	malloc, so we actually use the memory we allocate. */
86			71
87		setg_func = setg	72		setg_func = setg
88	-	attr = (pthread_attr_t)(malloc(unsafe.Sizeof(attr)))	73	+	pthread_attr_init(&attr)
89	-	if attr == nil {	74	+	pthread_attr_getstacksize(&attr, &size)
90	-	println("fakecgo: malloc failed")
91	-	abort()
92	-	}
93	-	pthread_attr_init(attr)
94	-	pthread_attr_getstacksize(attr, &size)
95		// runtime/cgo uses __builtin_frame_address(0) instead of `uintptr(unsafe.Pointer(&size))`	75		// runtime/cgo uses __builtin_frame_address(0) instead of `uintptr(unsafe.Pointer(&size))`
96		// but this should be OK since we are taking the address of the first variable in this function.	76		// but this should be OK since we are taking the address of the first variable in this function.
97		g.stacklo = uintptr(unsafe.Pointer(&size)) - uintptr(size) + 4096	77		g.stacklo = uintptr(unsafe.Pointer(&size)) - uintptr(size) + 4096
98	-	pthread_attr_destroy(attr)	78	+	pthread_attr_destroy(&attr)
99	-	free(unsafe.Pointer(attr))
100		}	79		}

M internal/fakecgo/go_linux.go +4 -25


@@ -67,34 +67,13 @@ var setg_func uintptr
67	67		//go:nosplit
68	68		func x_cgo_init(g *G, setg uintptr) {
69	69		var size size_t
70		-	var attr *pthread_attr_t
71		-
72		-	/* The memory sanitizer distributed with versions of clang
73		-	before 3.8 has a bug: if you call mmap before malloc, mmap
74		-	may return an address that is later overwritten by the msan
75		-	library. Avoid this problem by forcing a call to malloc
76		-	here, before we ever call malloc.
77		-
78		-	This is only required for the memory sanitizer, so it's
79		-	unfortunate that we always run it. It should be possible
80		-	to remove this when we no longer care about versions of
81		-	clang before 3.8. The test for this is
82		-	misc/cgo/testsanitizers.
83		-
84		-	GCC works hard to eliminate a seemingly unnecessary call to
85		-	malloc, so we actually use the memory we allocate. */
	70	+	var attr pthread_attr_t
86	71
87	72		setg_func = setg
88		-	attr = (pthread_attr_t)(malloc(unsafe.Sizeof(attr)))
89		-	if attr == nil {
90		-	println("fakecgo: malloc failed")
91		-	abort()
92		-	}
93		-	pthread_attr_init(attr)
94		-	pthread_attr_getstacksize(attr, &size)
	73	+	pthread_attr_init(&attr)
	74	+	pthread_attr_getstacksize(&attr, &size)
95	75		// runtime/cgo uses __builtin_frame_address(0) instead of `uintptr(unsafe.Pointer(&size))`
96	76		// but this should be OK since we are taking the address of the first variable in this function.
97	77		g.stacklo = uintptr(unsafe.Pointer(&size)) - uintptr(size) + 4096
98		-	pthread_attr_destroy(attr)
99		-	free(unsafe.Pointer(attr))
	78	+	pthread_attr_destroy(&attr)
100	79		}


@@ -67,34 +67,13 @@ var setg_func uintptr
67		//go:nosplit	67		//go:nosplit
68		func x_cgo_init(g *G, setg uintptr) {	68		func x_cgo_init(g *G, setg uintptr) {
69		var size size_t	69		var size size_t
70	-	var attr *pthread_attr_t	70	+	var attr pthread_attr_t
71	-
72	-	/* The memory sanitizer distributed with versions of clang
73	-	before 3.8 has a bug: if you call mmap before malloc, mmap
74	-	may return an address that is later overwritten by the msan
75	-	library. Avoid this problem by forcing a call to malloc
76	-	here, before we ever call malloc.
77	-
78	-	This is only required for the memory sanitizer, so it's
79	-	unfortunate that we always run it. It should be possible
80	-	to remove this when we no longer care about versions of
81	-	clang before 3.8. The test for this is
82	-	misc/cgo/testsanitizers.
83	-
84	-	GCC works hard to eliminate a seemingly unnecessary call to
85	-	malloc, so we actually use the memory we allocate. */
86			71
87		setg_func = setg	72		setg_func = setg
88	-	attr = (pthread_attr_t)(malloc(unsafe.Sizeof(attr)))	73	+	pthread_attr_init(&attr)
89	-	if attr == nil {	74	+	pthread_attr_getstacksize(&attr, &size)
90	-	println("fakecgo: malloc failed")
91	-	abort()
92	-	}
93	-	pthread_attr_init(attr)
94	-	pthread_attr_getstacksize(attr, &size)
95		// runtime/cgo uses __builtin_frame_address(0) instead of `uintptr(unsafe.Pointer(&size))`	75		// runtime/cgo uses __builtin_frame_address(0) instead of `uintptr(unsafe.Pointer(&size))`
96		// but this should be OK since we are taking the address of the first variable in this function.	76		// but this should be OK since we are taking the address of the first variable in this function.
97		g.stacklo = uintptr(unsafe.Pointer(&size)) - uintptr(size) + 4096	77		g.stacklo = uintptr(unsafe.Pointer(&size)) - uintptr(size) + 4096
98	-	pthread_attr_destroy(attr)	78	+	pthread_attr_destroy(&attr)
99	-	free(unsafe.Pointer(attr))
100		}	79		}

M internal/fakecgo/go_netbsd.go +4 -25


@@ -73,34 +73,13 @@ var setg_func uintptr
73	73		//go:nosplit
74	74		func x_cgo_init(g *G, setg uintptr) {
75	75		var size size_t
76		-	var attr *pthread_attr_t
77		-
78		-	/* The memory sanitizer distributed with versions of clang
79		-	before 3.8 has a bug: if you call mmap before malloc, mmap
80		-	may return an address that is later overwritten by the msan
81		-	library. Avoid this problem by forcing a call to malloc
82		-	here, before we ever call malloc.
83		-
84		-	This is only required for the memory sanitizer, so it's
85		-	unfortunate that we always run it. It should be possible
86		-	to remove this when we no longer care about versions of
87		-	clang before 3.8. The test for this is
88		-	misc/cgo/testsanitizers.
89		-
90		-	GCC works hard to eliminate a seemingly unnecessary call to
91		-	malloc, so we actually use the memory we allocate. */
	76	+	var attr pthread_attr_t
92	77
93	78		setg_func = setg
94		-	attr = (pthread_attr_t)(malloc(unsafe.Sizeof(attr)))
95		-	if attr == nil {
96		-	println("fakecgo: malloc failed")
97		-	abort()
98		-	}
99		-	pthread_attr_init(attr)
100		-	pthread_attr_getstacksize(attr, &size)
	79	+	pthread_attr_init(&attr)
	80	+	pthread_attr_getstacksize(&attr, &size)
101	81		// runtime/cgo uses __builtin_frame_address(0) instead of `uintptr(unsafe.Pointer(&size))`
102	82		// but this should be OK since we are taking the address of the first variable in this function.
103	83		g.stacklo = uintptr(unsafe.Pointer(&size)) - uintptr(size) + 4096
104		-	pthread_attr_destroy(attr)
105		-	free(unsafe.Pointer(attr))
	84	+	pthread_attr_destroy(&attr)
106	85		}


@@ -73,34 +73,13 @@ var setg_func uintptr
73		//go:nosplit	73		//go:nosplit
74		func x_cgo_init(g *G, setg uintptr) {	74		func x_cgo_init(g *G, setg uintptr) {
75		var size size_t	75		var size size_t
76	-	var attr *pthread_attr_t	76	+	var attr pthread_attr_t
77	-
78	-	/* The memory sanitizer distributed with versions of clang
79	-	before 3.8 has a bug: if you call mmap before malloc, mmap
80	-	may return an address that is later overwritten by the msan
81	-	library. Avoid this problem by forcing a call to malloc
82	-	here, before we ever call malloc.
83	-
84	-	This is only required for the memory sanitizer, so it's
85	-	unfortunate that we always run it. It should be possible
86	-	to remove this when we no longer care about versions of
87	-	clang before 3.8. The test for this is
88	-	misc/cgo/testsanitizers.
89	-
90	-	GCC works hard to eliminate a seemingly unnecessary call to
91	-	malloc, so we actually use the memory we allocate. */
92			77
93		setg_func = setg	78		setg_func = setg
94	-	attr = (pthread_attr_t)(malloc(unsafe.Sizeof(attr)))	79	+	pthread_attr_init(&attr)
95	-	if attr == nil {	80	+	pthread_attr_getstacksize(&attr, &size)
96	-	println("fakecgo: malloc failed")
97	-	abort()
98	-	}
99	-	pthread_attr_init(attr)
100	-	pthread_attr_getstacksize(attr, &size)
101		// runtime/cgo uses __builtin_frame_address(0) instead of `uintptr(unsafe.Pointer(&size))`	81		// runtime/cgo uses __builtin_frame_address(0) instead of `uintptr(unsafe.Pointer(&size))`
102		// but this should be OK since we are taking the address of the first variable in this function.	82		// but this should be OK since we are taking the address of the first variable in this function.
103		g.stacklo = uintptr(unsafe.Pointer(&size)) - uintptr(size) + 4096	83		g.stacklo = uintptr(unsafe.Pointer(&size)) - uintptr(size) + 4096
104	-	pthread_attr_destroy(attr)	84	+	pthread_attr_destroy(&attr)
105	-	free(unsafe.Pointer(attr))
106		}	85		}