mirror of
https://github.com/libguestfs/libguestfs.git
synced 2026-03-21 22:53:37 +00:00
e2f8db27d0
The current "arg_string_list" and "free_string_list" implementations go
back to commit b6f01f3260 ("Add Go (language) bindings.", 2013-07-03).
There are two problems with them:
- "free_string_list" doesn't actually free anything,
- at the *first* such g.Internal_test() call site that passes an
Ostringlist member inside the Optargs argument, namely:
> g.Internal_test ("abc",
> string_addr ("def"),
> []string{},
> false,
> 0,
> 0,
> "123",
> "456",
> []byte{'a', 'b', 'c', '\000', 'a', 'b', 'c'},
> &guestfs.OptargsInternal_test{Ostringlist_is_set: true,
> Ostringlist: []string{}
> }
> )
the "golang/run-bindtests" case crashes:
> panic: runtime error: cgo argument has Go pointer to Go pointer
>
> goroutine 1 [running]:
> libguestfs.org/guestfs.(*Guestfs).Internal_test.func7(0xc000018180,
> 0xadfb60, 0xadfb80, 0xc000010048, 0x0, 0x0, 0x0, 0xae3e10, 0xae3e30,
> 0xade3a0, ...)
> golang/src/libguestfs.org/guestfs/guestfs.go:6729 +0xa9
> libguestfs.org/guestfs.(*Guestfs).Internal_test(0xc000018180, 0x4ee3a5,
> 0x3, 0xc000061be8, 0xc000061af8, 0x0, 0x0, 0xc000061a00, 0x0, 0x0, ...)
> golang/src/libguestfs.org/guestfs/guestfs.go:6729 +0x3c9
> main.main()
> golang/bindtests/bindtests.go:77 +0x151e
> exit status 2
> FAIL run-bindtests (exit status: 1)
In Daniel P. Berrangé's words [1],
> You're allowed to pass a Go pointer to C via CGo, but the memory that
> points to is not allowed to contained further Go pointers. So the struct
> fields must strictly use a C pointer.
One pattern to solve the problem has been shown on stackoverflow [2].
Thus, rewrite the "arg_string_list" and "free_string_list" functions
almost entirely in C, following that example.
While this approach is not the most idiomatic Go, as a solution exists
without C helper functions [3], it should still be acceptable, at least as
an incremental improvement, for letting "golang/run-bindtests" pass.
[1] https://listman.redhat.com/archives/libguestfs/2021-September/msg00118.html
[2] https://stackoverflow.com/questions/35924545/golang-cgo-panic-runtime-error-cgo-argument-has-go-pointer-to-go-pointer
[3] https://listman.redhat.com/archives/libguestfs/2021-September/msg00106.html
Cc: "Daniel P. Berrangé" <berrange@redhat.com>
Cc: "Richard W.M. Jones" <rjones@redhat.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20210921192939.32468-1-lersek@redhat.com>
Tested-by: "Richard W.M. Jones" <rjones@redhat.com>
Acked-by: "Richard W.M. Jones" <rjones@redhat.com>
Libguestfs is tools and a library for accessing and modifying guest disk images. For more information see the home page: http://libguestfs.org/ For discussion, development, patches, etc. please use the mailing list: http://www.redhat.com/mailman/listinfo/libguestfs To find out how to build libguestfs from source, read: docs/guestfs-building.pod http://libguestfs.org/guestfs-building.1.html man docs/guestfs-building.1 Copyright (C) 2009-2020 Red Hat Inc. The library is distributed under the LGPLv2+. The programs are distributed under the GPLv2+. Please see the files COPYING and COPYING.LIB for full license information. The examples are under a very liberal license.