golang checkptr 代码
文件路径：/src/runtime/checkptr.go
/ Copyright 2019 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.
package runtime
import "unsafe"
func checkptrAlignment(p unsafe.Pointer, elem *_type, n uintptr) {
/ nil pointer is always suitably aligned (#47430).
if p == nil {
return
}
/ Check that (*[n]elem)(p) is appropriately aligned.
/ Note that we allow unaligned pointers if the types they point to contain
/ no pointers themselves. See issue 37298.
/ TODO(mdempsky): What about fieldAlign?
if elem.ptrdata != 0 && uintptr(p)&(uintptr(elem.align)-1) != 0 {
throw("checkptr: misaligned pointer conversion")
}
/ Check that (*[n]elem)(p) doesn't straddle multiple heap objects.
/ TODO(mdempsky): Fix #46938 so we don't need to worry about overflow here.
if checkptrStraddles(p, n*elem.size) {
throw("checkptr: converted pointer straddles multiple allocations")
}
}
/ checkptrStraddles reports whether the first size-bytes of memory
/ addressed by ptr is known to straddle more than one Go allocation.
func checkptrStraddles(ptr unsafe.Pointer, size uintptr) bool {
if size <= 1 {
return false
}
/ Check that add(ptr, size-1) won't overflow. This avoids the risk
/ of producing an illegal pointer value (assuming ptr is legal).
if uintptr(ptr) >= -(size - 1) {
return true
}
end := add(ptr, size-1)
/ TODO(mdempsky): Detect when [ptr, end] contains Go allocations,
/ but neither ptr nor end point into one themselves.
return checkptrBase(ptr) != checkptrBase(end)
}
func checkptrArithmetic(p unsafe.Pointer, originals []unsafe.Pointer) {
if 0 < uintptr(p) && uintptr(p) < minLegalPointer {
throw("checkptr: pointer arithmetic computed bad pointer value")
}
/ Check that if the computed pointer p points into a heap
/ object, then one of the original pointers must have pointed
/ into the same object.
base := checkptrBase(p)
if base == 0 {
return
}
for _, original := range originals {
if base == checkptrBase(original) {
return
}
}
throw("checkptr: pointer arithmetic result points to invalid allocation")
}
/ checkptrBase returns the base address for the allocation containing
/ the address p.
/
/ Importantly, if p1 and p2 point into the same variable, then
/ checkptrBase(p1) == checkptrBase(p2). However, the converse/inverse
/ is not necessarily true as allocations can have trailing padding,
/ and multiple variables may be packed into a single allocation.
func checkptrBase(p unsafe.Pointer) uintptr {
/ stack
if gp := getg(); gp.stack.lo <= uintptr(p) && uintptr(p) < gp.stack.hi {
/ TODO(mdempsky): Walk the stack to identify the
/ specific stack frame or even stack object that p
/ points into.
/
/ In the mean time, use "1" as a pseudo-address to
/ represent the stack. This is an invalid address on
/ all platforms, so it's guaranteed to be distinct
/ from any of the addresses we might return below.
return 1
}
/ heap (must check after stack because of #35068)
if base, _, _ := findObject(uintptr(p), 0, 0); base != 0 {
return base
}
/ data or bss
for _, datap := range activeModules() {
if datap.data <= uintptr(p) && uintptr(p) < datap.edata {
return datap.data
}
if datap.bss <= uintptr(p) && uintptr(p) < datap.ebss {
return datap.bss
}
}
return 0
}