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cmd/cgo: always use a function literal for pointer checking

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The pointer checking code needs to know the exact type of the parameter
expected by the C function, so that it can use a type assertion to
convert the empty interface returned by cgoCheckPointer to the correct
type. Previously this was done by using a type conversion, but that
meant that the code accepted arguments that were convertible to the
parameter type, rather than arguments that were assignable as in a
normal function call. In other words, some code that should not have
passed type checking was accepted.

This CL changes cgo to always use a function literal for pointer
checking. Now the argument is passed to the function literal, which has
the correct argument type, so type checking is performed just as for a
function call as it should be.

Since we now always use a function literal, simplify the checking code
to run as a statement by itself. It now no longer needs to return a
value, and we no longer need a type assertion.

This does have the cost of introducing another function call into any
call to a C function that requires pointer checking, but the cost of the
additional call should be minimal compared to the cost of pointer
checking.

Fixes #16591.

Change-Id: I220165564cf69db9fd5f746532d7f977a5b2c989
Reviewed-on: https://go-review.googlesource.com/31233
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
This commit is contained in:
Ian Lance Taylor 2016-10-14 14:53:59 -07:00
parent e32ac7978d
commit a16954b8a7
6 changed files with 121 additions and 94 deletions
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13
src/cmd/cgo/out.go
View file

@ -1379,14 +1379,14 @@ func _cgo_runtime_cgocall(unsafe.Pointer, uintptr) int32
func _cgo_runtime_cgocallback(unsafe.Pointer, unsafe.Pointer, uintptr, uintptr)
//go:linkname _cgoCheckPointer runtime.cgoCheckPointer
func _cgoCheckPointer(interface{}, ...interface{}) interface{}
func _cgoCheckPointer(interface{}, ...interface{})
//go:linkname _cgoCheckResult runtime.cgoCheckResult
func _cgoCheckResult(interface{})
`
const gccgoGoProlog = `
func _cgoCheckPointer(interface{}, ...interface{}) interface{}
func _cgoCheckPointer(interface{}, ...interface{})
func _cgoCheckResult(interface{})
`
@ -1566,18 +1566,17 @@ typedef struct __go_empty_interface {
void *__object;
} Eface;
extern Eface runtimeCgoCheckPointer(Eface, Slice)
extern void runtimeCgoCheckPointer(Eface, Slice)
__asm__("runtime.cgoCheckPointer")
__attribute__((weak));
extern Eface localCgoCheckPointer(Eface, Slice)
extern void localCgoCheckPointer(Eface, Slice)
__asm__("GCCGOSYMBOLPREF._cgoCheckPointer");
Eface localCgoCheckPointer(Eface ptr, Slice args) {
void localCgoCheckPointer(Eface ptr, Slice args) {
if(runtimeCgoCheckPointer) {
return runtimeCgoCheckPointer(ptr, args);
runtimeCgoCheckPointer(ptr, args);
}
return ptr;
}
extern void runtimeCgoCheckResult(Eface)