[xen master] golang/xenlight: fix StringList toC conversion

[patchbot@xxxxxxx]

commit 1422d8db1b3dfdf7d9179944e594876e5e356a4b
Author:     Nick Rosbrook <rosbrookn@xxxxxxxxx>
AuthorDate: Mon May 24 16:36:43 2021 -0400
Commit:     George Dunlap <george.dunlap@xxxxxxxxxx>
CommitDate: Mon Jun 21 16:49:08 2021 +0100

    golang/xenlight: fix StringList toC conversion
    
    The current implementation of StringList.toC does not correctly account
    for how libxl_string_list is expected to be laid out in C, which is clear
    when one looks at libxl_string_list_length in libxl.c. In particular,
    StringList.toC does not account for the extra memory that should be
    allocated for the "sentinel" entry. And, when using the "slice trick" to
    create a slice that can address C memory, the unsafe.Pointer conversion
    should be on a C.libxl_string_list, not *C.libxl_string_list.
    
    Fix these problems by (1) allocating an extra slot in the slice used to
    address the C memory, and explicity set the last entry to nil so the C
    memory will be zeroed out, and (2) dereferencing csl in the
    unsafe.Pointer conversion.
    
    Signed-off-by: Nick Rosbrook <rosbrookn@xxxxxxxxxxxx>
    Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx>
---
 tools/golang/xenlight/xenlight.go | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/golang/xenlight/xenlight.go 
b/tools/golang/xenlight/xenlight.go
index b9189dec5c..13171d0ad1 100644
--- a/tools/golang/xenlight/xenlight.go
+++ b/tools/golang/xenlight/xenlight.go
@@ -491,13 +491,14 @@ func (sl *StringList) fromC(csl *C.libxl_string_list) 
error {
 
 func (sl StringList) toC(csl *C.libxl_string_list) error {
        var char *C.char
-       size := len(sl)
+       size := len(sl) + 1
        *csl = (C.libxl_string_list)(C.malloc(C.ulong(size) * 
C.ulong(unsafe.Sizeof(char))))
-       clist := (*[1 << 30]*C.char)(unsafe.Pointer(csl))[:size:size]
+       clist := (*[1 << 30]*C.char)(unsafe.Pointer(*csl))[:size:size]
 
        for i, v := range sl {
                clist[i] = C.CString(v)
        }
+       clist[len(clist)-1] = nil
 
        return nil
 }
--
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