x86: add module symbol import test

Symbol namespace imports end up as "import_ns=<value>" strings inside
the ELF .modinfo section.  If a kpatch needs to import a namespace, it
may result in a modified .modinfo section that kpatch-build needs to
carefully handle: the string is extracted from the patched ELF object
and saved in the output ELF object .modinfo section.

Add a test that verifies that four namespaces are successfully
re-imported by create-diff-object.  The following patch produced the
import-ns.{ORIG,PATCHED}.o files:

  diff -Nupr src.orig/fs/proc/cmdline.c src/fs/proc/cmdline.c
  --- src.orig/fs/proc/cmdline.c	2022-10-24 15:41:08.858760066 -0400
  +++ src/fs/proc/cmdline.c	2022-10-24 15:41:11.698715352 -0400
  @@ -4,10 +4,23 @@
   #include <linux/proc_fs.h>
   #include <linux/seq_file.h>

  +#include <linux/module.h>
  +
  +MODULE_IMPORT_NS(DMA_BUF);
  +MODULE_IMPORT_NS(DEVMEM);
  +MODULE_IMPORT_NS(KPATCH_TEST);		/* dummy import to inflate .modinfo */
  +MODULE_IMPORT_NS(KPATCH_TEST2);		/* dummy import to inflate .modinfo */
  +extern void dma_buf_export(void *);
  +extern int cpu_cache_invalidate_memregion(int);
  +
   static int cmdline_proc_show(struct seq_file *m, void *v)
   {
  -	seq_puts(m, saved_command_line);
  -	seq_putc(m, '\n');
  +	seq_printf(m, "%s kpatch=1\n", saved_command_line);
  +
  +	/* test namespace import */
  +	pr_info("dma_buf_export=%pK", dma_buf_export);
  +	pr_info("cpu_cache_invalidate_memregion=%pK", cpu_cache_invalidate_memregion);
  +
   	return 0;
   }

Signed-off-by: Joe Lawrence <[email protected]>

Author: joe-lawrence

x86_64/import-ns.ORIG.o

@@ -0,0 +1,15 @@
+#!/bin/bash
+source $KPATCH_TEST_LIBRARY
+
+TESTFILE=$(basename "$0")
+OUTFILE=${TESTFILE%.test}.OUTPUT.o
+
+# Verify there are four namespace imports in the resulting .modinfo section, e.g.
+#
+#   String dump of section '.modinfo':
+#     [     0]  import_ns=KPATCH_TEST2
+#     [    17]  import_ns=KPATCH_TEST
+#     [    2d]  import_ns=DEVMEM
+#     [    3e]  import_ns=DMA_BUF
+
+[[ $(readelf --wide --string-dump=.modinfo "$OUTFILE" | grep --count -e 'import_ns=') == 4 ]]