On Wed, Jan 20, 2016 at 11:04:24AM +0100, Ard Biesheuvel wrote:

On 20 January 2016 at 10:43, Heiko Carstens [off-list ref] wrote:

quoted

On Wed, Jan 20, 2016 at 10:05:37AM +0100, Ard Biesheuvel wrote:

quoted

This enables the newly introduced text-relative kallsyms support when
building 64-bit targets. This cuts the size of the kallsyms address
table in half, reducing the memory footprint of the kernel .rodata
section by about 250 KB for a defconfig build.

Signed-off-by: Ard Biesheuvel <redacted>
---

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index dbeeb3a049f2..588160fd1db0 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig

@@ -149,6 +149,7 @@ config S390
      select HAVE_REGS_AND_STACK_ACCESS_API
      select HAVE_SYSCALL_TRACEPOINTS
      select HAVE_VIRT_CPU_ACCOUNTING
+     select KALLSYMS_TEXT_RELATIVE if 64BIT

Please remove the "if 64BIT" since s390 is always 64BIT in the meantime.
Tested on s390 and everything seems still to work ;)

Acked-by: Heiko Carstens <redacted>

Thanks! Did you take a look at /proc/kallsyms, by any chance? It
should look identical with and without these patches

Close to identical, since the generated code and offsets change a bit with
your new config option enabled and disabled. But only those parts that are
linked behind kernel/kallsyms.c.

However I did run a couple of ftrace, kprobes tests and enforced call
backtraces. Everything still works.

So it looks all good.