[Xen-API] [PATCH 5 of 5 v3] tools/ocaml: libxc bindings: Fix failwith_xc()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

The static error_str[] buffer is not thread-safe, and 1024 bytes is
unreasonably large.  Reduce to 256 bytes (which is still much larger than any
current use), and move it to being a stack variable.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

--
Changes since v1:
 * Mark as Noreturn, due to unconditional use of caml_raise_with_string()

diff -r 7a33b4fdb977 -r 189d76dca2e4 tools/ocaml/libs/xc/xenctrl_stubs.c
--- a/tools/ocaml/libs/xc/xenctrl_stubs.c
+++ b/tools/ocaml/libs/xc/xenctrl_stubs.c
@@ -51,21 +51,22 @@
        i1 = (uint32_t) Int64_val(Field(input, 0)); \
        i2 = ((Field(input, 1) == Val_none) ? 0xffffffff : (uint32_t) 
Int64_val(Field(Field(input, 1), 0)));
 
-#define ERROR_STRLEN 1024
-void failwith_xc(xc_interface *xch)
+static void Noreturn failwith_xc(xc_interface *xch)
 {
-       static char error_str[ERROR_STRLEN];
+       char error_str[256];
        if (xch) {
                const xc_error *error = xc_get_last_error(xch);
                if (error->code == XC_ERROR_NONE)
-                       snprintf(error_str, ERROR_STRLEN, "%d: %s", errno, 
strerror(errno));
+                       snprintf(error_str, sizeof(error_str),
+                                "%d: %s", errno, strerror(errno));
                else
-                       snprintf(error_str, ERROR_STRLEN, "%d: %s: %s",
-                                error->code,
+                       snprintf(error_str, sizeof(error_str),
+                                "%d: %s: %s", error->code,
                                 xc_error_code_to_desc(error->code),
                                 error->message);
        } else {
-               snprintf(error_str, ERROR_STRLEN, "Unable to open XC 
interface");
+               snprintf(error_str, sizeof(error_str),
+                        "Unable to open XC interface");
        }
        caml_raise_with_string(*caml_named_value("xc.error"), error_str);
 }

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