[PATCH] scripts/kallsyms: filter symbols not in kernel address space

On Monday 28 October 2013, Ming Lei wrote:

quoted

This patch uses CONFIG_PAGE_OFFSET to filter symbols which
are not in kernel address space because these symbols are
generally for generating code purpose and can't be run at
kernel mode, so we needn't keep them in /proc/kallsyms.

For example, on ARM there are some symbols which are
linked in relocatable code section, then perf can't parse
symbols any more from /proc/kallsyms, and this patch fixes
the problem.

Cc: Russell King <redacted>
Cc: linux-arm-kernel at lists.infradead.org
Cc: Michal Marek <redacted>
Acked-by: Rusty Russell <redacted>
Signed-off-by: Ming Lei <tom.leiming@gmail.com>

Sorry for the late report, but I seem to have encountered a problem with this
patch, now that it has made it into all stable kernels.

When linking an ARM nommu kernel, I get the output "No valid symbol." twice,
from scripts/kallsyms. The problem evidently is that PAGE_OFFSET is still
set to 0xC0000000 on ARM NOMMU builds but the kernel is linked to start at
PLAT_PHYS_OFFSET instead, which may be elsehwere. For most platforms,
this is defined in Kconfig these days, so we could get away with

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index d1e4098..c477a7c 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig

@@ -1592,6 +1592,7 @@ endchoice

 config PAGE_OFFSET
        hex
+       default PHYS_OFFSET if !MMU
        default 0x40000000 if VMSPLIT_1G
        default 0x80000000 if VMSPLIT_2G
        default 0xC0000000

but there are still a few ARM platforms that define their own PLAT_PHYS_OFFSET
in memory.h, and it wouldn't help on non-ARM systems that might have the same
problem.