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net: allocate res_state entirely in C memory

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The linux-amd64-wsl builder was failing because the res_nsearch
implementation was storing pointer to the res_state's own fields
in other fields in the res_state. If the res_state is Go memory, this
looks like pointers to Go pointers. Moving the res_state to C memory
avoids the problem.

The linux-amd64-wsl builder has been fixed a different way by
replacing res_nsearch with res_search on Linux, where it is thread-safe.
But other systems that still need to use res_nsearch (such as macOS)
may run into the same kind of problem, so it is probably still worth
arranging for the res_state to live entirely in C memory.

Fixes #56658 (again).

Change-Id: I58a14e72c866eaceb02ad828854a1f626b9b8e73
Reviewed-on: https://go-review.googlesource.com/c/go/+/448798
Run-TryBot: Russ Cox <rsc@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
This commit is contained in:
Russ Cox 2022-11-08 16:16:44 -05:00 committed by Gopher Robot
parent 8befe0e408
commit 896faf306c
1 changed files with 5 additions and 4 deletions
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9
src/net/cgo_unix.go
View File

@ -331,11 +331,12 @@ func cgoLookupCNAME(ctx context.Context, name string) (cname string, err error,
// resSearch will make a call to the 'res_nsearch' routine in the C library
// and parse the output as a slice of DNS resources.
func resSearch(ctx context.Context, hostname string, rtype, class int) ([]dnsmessage.Resource, error) {
var state _C_struct___res_state
if err := _C_res_ninit(&state); err != nil {
state := (*_C_struct___res_state)(_C_malloc(unsafe.Sizeof(_C_struct___res_state{})))
defer _C_free(unsafe.Pointer(state))
if err := _C_res_ninit(state); err != nil {
return nil, errors.New("res_ninit failure: " + err.Error())
}
defer _C_res_nclose(&state)
defer _C_res_nclose(state)
// Some res_nsearch implementations (like macOS) do not set errno.
// They set h_errno, which is not per-thread and useless to us.
@ -350,7 +351,7 @@ func resSearch(ctx context.Context, hostname string, rtype, class int) ([]dnsmes
defer _C_free(unsafe.Pointer(buf))
s := _C_CString(hostname)
defer _C_FreeCString(s)
size, err := _C_res_nsearch(&state, s, class, rtype, buf, bufSize)
size, err := _C_res_nsearch(state, s, class, rtype, buf, bufSize)
if size <= 0 || size > bufSize {
return nil, errors.New("res_nsearch failure")
}