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rpc/dataconn: audit and comment use of unsafe for readv usage

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Go 1.13 will add a more precise escape analysis:
https://tip.golang.org/doc/go1.13#compiler

Reviewed usage of unsafe to ensure we adhere to the unsafe.Pointer safety rules:
https://tip.golang.org/pkg/unsafe/#Pointer
This commit is contained in:
Christian Schwarz 2019-07-17 23:55:18 +02:00
parent c4be60c29f
commit 95e16f01c1
1 changed files with 14 additions and 0 deletions
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14
rpc/dataconn/timeoutconn/timeoutconn.go
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@ -244,6 +244,14 @@ func (c Conn) readv(rawConn syscall.RawConn, iovecs []syscall.Iovec) (n int64, e
func (c Conn) doOneReadv(rawConn syscall.RawConn, iovecs *[]syscall.Iovec) (n int64, err error) { func (c Conn) doOneReadv(rawConn syscall.RawConn, iovecs *[]syscall.Iovec) (n int64, err error) {
rawReadErr := rawConn.Read(func(fd uintptr) (done bool) { rawReadErr := rawConn.Read(func(fd uintptr) (done bool) {
// iovecs, n and err must not be shadowed! // iovecs, n and err must not be shadowed!
// NOTE: unsafe.Pointer safety rules
// https://tip.golang.org/pkg/unsafe/#Pointer
//
// (4) Conversion of a Pointer to a uintptr when calling syscall.Syscall.
// ...
// uintptr() conversions must appear within the syscall.Syscall argument list.
// (even though we are not the escape analysis Likely not )
thisReadN, _, errno := syscall.Syscall( thisReadN, _, errno := syscall.Syscall(
syscall.SYS_READV, syscall.SYS_READV,
fd, fd,
@ -268,6 +276,12 @@ func (c Conn) doOneReadv(rawConn syscall.RawConn, iovecs *[]syscall.Iovec) (n in
left -= int64((*iovecs)[0].Len) left -= int64((*iovecs)[0].Len)
*iovecs = (*iovecs)[1:] *iovecs = (*iovecs)[1:]
} else { } else {
// NOTE: unsafe.Pointer safety rules
// https://tip.golang.org/pkg/unsafe/#Pointer
// (3) Conversion of a Pointer to a uintptr and back, with arithmetic.
// ...
// Note that both conversions must appear in the same expression,
// with only the intervening arithmetic between them:
(*iovecs)[0].Base = (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer((*iovecs)[0].Base)) + uintptr(left))) (*iovecs)[0].Base = (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer((*iovecs)[0].Base)) + uintptr(left)))
(*iovecs)[0].Len = uint64(curVecNewLength) (*iovecs)[0].Len = uint64(curVecNewLength)
break // inner break // inner