[ts-7000] FYI: Fix for the "undefined reference to `__umoddi3' / `__udivdi3'" error

["kaiwanbillimoria" <>]

Hey all,

I faced an issue when building a 2.6.24-based kernel for the TS72xx
(in particular, TS7200) using Matt's 2.6.24.4-ts7200-matt-10 patch
(you can get it from the 'Files' section; thanks Matt!).

Am posting this fyi, in case others come across a similar issue.


Issue:
------
$ make CROSS_COMPILE=arm-none-linux-gnueabi-
...
...
 LD      .tmp_vmlinux1

kernel/built-in.o: In function `timekeeping_resume':

utsname_sysctl.c:(.text+0x23a24): undefined reference to `__umoddi3'

utsname_sysctl.c:(.text+0x23a40): undefined reference to `__udivdi3'

kernel/built-in.o: In function `update_wall_time':

utsname_sysctl.c:(.text+0x2407c): undefined reference to `__umoddi3'

utsname_sysctl.c:(.text+0x24098): undefined reference to `__udivdi3'

make: *** [.tmp_vmlinux1] Error 1

$

Turns out this issue has been faced before; it's due to gcc
optimization (what else). The solution is to prevent gcc-3.4
optimization by inserting an inline assembler statement in
include/linux/time.h .

The "patch" is:
--------
Prevent gcc-4.3 form "optimizing" the while loop into a costly modulo
operation.
Patch found at http://lkml.org/lkml/2008/2/22/464.

Reported-by: Sven Rebhan <>
Signed-off-by: Segher Boessenkool <>
---
 include/linux/time.h |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/include/linux/time.h b/include/linux/time.h
index b04136d..3e8fd9e 100644
     ns += a->tv_nsec; 
     while(unlikely(ns >= NSEC_PER_SEC)) {   
              /* The following asm() prevents the compiler from 
                * optimising this loop into a modulo operation.  */   
                asm("" : "+r"(ns)); 
                ns -= NSEC_PER_SEC; 
                a->tv_sec++; 
     }

Original link:
https://dev.openwrt.org/browser/trunk/target/linux/s3c24xx/patches-2.6.24/1300-fix-gcc-4.3-false-modulo-optimization.patch.patch?rev=13613

[Toolchain: CodeSourcery GNU EABI ver 2008q3. Link:
http://www.codesourcery.com/gnu_toolchains/arm/portal/package3696/public/arm-none-linux-gnueabi/arm-2008q3-72-arm-none-linux-gnueabi-i686-pc-linux-gnu.tar.bz2
]

Also, I found that it hangs upon uncompressing if you turn ARM EABI
on, default is off (in Matt's config).

-Kaiwan.


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