kbuild: include core debug info when DEBUG_INFO_REDUCED

With CONFIG_DEBUG_INFO_REDUCED, we do get quite a lot of debug info
(around 22.7 MB for a defconfig+DEBUG_INFO_REDUCED). However, the
"basenames must match" rule used by -femit-struct-debug-baseonly
option means that we miss some core data structures, such as struct
{device, file, inode, mm_struct, page} etc.

We can easily get these included as well, while still getting the
benefits of CONFIG_DEBUG_INFO_REDUCED (faster build times and smaller
individual object files): All it takes is a dummy translation unit
including a few strategic headers and compiled with a flag overriding
-femit-struct-debug-baseonly.

This increases the size of .debug_info by ~0.3%, but these 90 KB
contain some rather useful info.
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Michal Marek <mmarek@suse.cz>

lib/Makefile

@@ -45,6 +45,9 @@ CFLAGS_kobject.o += -DDEBUG
 CFLAGS_kobject_uevent.o += -DDEBUG
 endif
 
+obj-$(CONFIG_DEBUG_INFO_REDUCED) += debug_info.o
+CFLAGS_debug_info.o += $(call cc-option, -femit-struct-debug-detailed=any)
+
 obj-$(CONFIG_GENERIC_IOMAP) += iomap.o
 obj-$(CONFIG_GENERIC_PCI_IOMAP) += pci_iomap.o
 obj-$(CONFIG_HAS_IOMEM) += iomap_copy.o devres.o

lib/debug_info.c

+/*
+ * This file exists solely to ensure debug information for some core
+ * data structures is included in the final image even for
+ * CONFIG_DEBUG_INFO_REDUCED. Please do not add actual code. However,
+ * adding appropriate #includes is fine.
+ */
+#include <stdarg.h>
+
+#include <linux/cred.h>
+#include <linux/crypto.h>
+#include <linux/dcache.h>
+#include <linux/device.h>
+#include <linux/fs.h>
+#include <linux/fscache-cache.h>
+#include <linux/io.h>
+#include <linux/kallsyms.h>
+#include <linux/kernel.h>
+#include <linux/kobject.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/net.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <net/addrconf.h>
+#include <net/sock.h>
+#include <net/tcp.h>