Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

[Russell King (Oracle)]

On Thu, May 30, 2024 at 05:50:52PM +0530, Naresh Kamboju wrote:
> The arm builds failed on Linux next with gcc-13 and clang-18.
> 
> Config: arm imx_v6_v7_defconfig - failed
> 
> Reported-by: Linux Kernel Functional Testing <lkft@xxxxxxxxxx>
> 
> Build log:
> -----
> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> `rcu_trc_cmpxchg_need_qs':
> update.c:(.text+0x348): undefined reference to `__bad_cmpxchg'
> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> `rcu_read_unlock_trace_special':
> update.c:(.text+0x41c): undefined reference to `__bad_cmpxchg'
> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function
> `trc_read_check_handler':
> update.c:(.text+0x4b0): undefined reference to `__bad_cmpxchg'
> arm-linux-gnueabihf-ld: kernel/rcu/update.o: in function `trc_inspect_reader':
> update.c:(.text+0x1518): undefined reference to `__bad_cmpxchg'
> arm-linux-gnueabihf-ld: update.c:(.text+0x1548): undefined reference
> to `__bad_cmpxchg'
> arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4):
> more undefined references to `__bad_cmpxchg' follow
> make[3]: *** [/builds/linux/scripts/Makefile.vmlinux:34: vmlinux] Error 1

You get a reference to __bad_cmpxchg() when someone uses cmpxchg() on
a datatype that there are no CPU instructions to perform the atomic
compare-and-exchange.

As we support 8-bit, 16-bit and 32-bit, I would expect that we're now
seeing cmpxchg() being used on 64-bit values, which are unsupportable
on 32-bit Arm.

-- 
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