kbuild: modversions: add infrastructure for emitting relative CRCs

This add the kbuild infrastructure that will allow architectures to emit
vmlinux symbol CRCs as 32-bit offsets to another location in the kernel
where the actual value is stored. This works around problems with CRCs
being mistaken for relocatable symbols on kernels that self relocate at
runtime (i.e., powerpc with CONFIG_RELOCATABLE=y)

For the kbuild side of things, this comes down to the following:

 - introducing a Kconfig symbol MODULE_REL_CRCS

 - adding a -R switch to genksyms to instruct it to emit the CRC symbols
   as references into the .rodata section

 - making modpost distinguish such references from absolute CRC symbols
   by the section index (SHN_ABS)

 - making kallsyms disregard non-absolute symbols with a __crc_ prefix

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 299b92ca1ae0..5d554419170b 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -219,6 +219,10 @@ static int symbol_valid(struct sym_entry *s)
 		"_SDA2_BASE_",		/* ppc */
 		NULL };
 
+	static char *special_prefixes[] = {
+		"__crc_",		/* modversions */
+		NULL };
+
 	static char *special_suffixes[] = {
 		"_veneer",		/* arm */
 		"_from_arm",		/* arm */
@@ -259,6 +263,14 @@ static int symbol_valid(struct sym_entry *s)
 		if (strcmp(sym_name, special_symbols[i]) == 0)
 			return 0;
 
+	for (i = 0; special_prefixes[i]; i++) {
+		int l = strlen(special_prefixes[i]);
+
+		if (l <= strlen(sym_name) &&
+		    strncmp(sym_name, special_prefixes[i], l) == 0)
+			return 0;
+	}
+
 	for (i = 0; special_suffixes[i]; i++) {
 		int l = strlen(sym_name) - strlen(special_suffixes[i]);