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Re: [Xen-devel] [PATCH v4] kexec-tools: Perform run-time linking of libxenctrl.so

I've implemented your feedback and posted the following:

[PATCH v1] kexec-tools: Tweak run-time handling of libxenctrl.so


On 01/18/2018 05:55 AM, Daniel Kiper wrote:
On Wed, Jan 17, 2018 at 10:39:01AM -0600, Eric DeVolder wrote:
When kexec is utilized in a Xen environment, it has an explicit
run-time dependency on libxenctrl.so. This dependency occurs
during the configure stage and when building kexec-tools.


As I saw Simon applied the patch. Great! Sadly I have just
realized that I have missed two things. Please look below.

The patch creates a wrapper function around xc_interface_open()
and xc_interface_close() to perform the dlopen() and dlclose().

You say about dlclose() here...

diff --git a/kexec/kexec-xen.h b/kexec/kexec-xen.h
new file mode 100644
index 0000000..ffb8743
--- /dev/null
+++ b/kexec/kexec-xen.h


+/* The handle from dlopen(), needed by dlsym(), dlclose() */
+extern void *xc_dlhandle;

...and here but it is never called. Is it by design or by mistake?
If by design please add a comment saying why into relevant place,
e.g. __xc_interface_close()? If by mistake please fix it.


+/* The handle from dlopen(), needed by dlsym(), dlclose() */
+extern void *xc_dlhandle;

I am still not happy with xc_dlhandle being extern. IMO it should be static.
I have missed that during last review. Sorry about that. I have a feeling
that you can easily fix it.

Define __xc_dlsym() in kexec/kexec-xen.c just before __xc_interface_open() like 

void *__xc_dlsym(const char *symbol)
   return dlsym(xc_dlhandle, symbol);

+/* Wrappers around xc_interface_open/close() to insert dlopen/dlclose() */
+xc_interface *__xc_interface_open(xentoollog_logger *logger,
+                                 xentoollog_logger *dombuild_logger,
+                                 unsigned open_flags);
+int __xc_interface_close(xc_interface *xch);
+/* GCC expression statements for evaluating dlsym() */
+#define __xc_call(dtype, name, args...) \
+( \
+       { dtype value; \
+       typedef dtype (*func_t)(xc_interface *, ...); \
+       func_t func = dlsym(xc_dlhandle, #name); \

And then replace dlsym(xc_dlhandle, #name) with __xc_dlsym(#name)...

+       value = func(args); \
+       value; } \
+#define __xc_data(dtype, name) \
+( \
+       { dtype *value = (dtype *)dlsym(xc_dlhandle, #name); value; } \

...and here. Additionally, you can use __xc_dlsym() instead of dlsym()
in other places in your patch. Latter is not a must...


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