Re: [PATCH v8 02/17] xen: introduce generic non-atomic test_*bit()

[Jan Beulich <jbeulich@xxxxxxxx>]

On 03.05.2024 19:15, Oleksii wrote:
> On Thu, 2024-04-25 at 17:35 +0200, Jan Beulich wrote:
>>>   #include <asm/bitops.h>
>>>   
>>> +#ifndef arch_check_bitop_size
>>> +#define arch_check_bitop_size(addr)
>>
>> Can this really do nothing? Passing the address of an object smaller
>> than
>> bitop_uint_t will read past the object in the generic__*_bit()
>> functions.
> It seems RISC-V isn' happy with the following generic definition:
>    extern void __bitop_bad_size(void);
>    
>    /* --------------------- Please tidy above here --------------------
>    - */
>    
>    #include <asm/bitops.h>
>    
>    #ifndef arch_check_bitop_size
>    
>    #define bitop_bad_size(addr) sizeof(*(addr)) < sizeof(bitop_uint_t)
>    
>    #define arch_check_bitop_size(addr) \
>        if ( bitop_bad_size(addr) ) __bitop_bad_size();
>    
>    #endif /* arch_check_bitop_size */

I'm afraid you've re-discovered something that was also found during the
original Arm porting effort. As nice and logical as it would (seem to) be
to have bitop_uint_t match machine word size, there are places ...

> The following errors occurs. bitop_uint_t for RISC-V is defined as
> unsigned long for now:

... where we assume such operations can be done on 32-bit quantities.

Jan

>     ./common/symbols-dummy.o -o ./.xen-syms.0
> riscv64-linux-gnu-ld: prelink.o: in function `atomic_sub':
> /build/xen/./arch/riscv/include/asm/atomic.h:152: undefined reference
> to `__bitop_bad_size'
> riscv64-linux-gnu-ld: prelink.o: in function `evtchn_check_pollers':
> /build/xen/common/event_channel.c:1531: undefined reference to
> `__bitop_bad_size'
> riscv64-linux-gnu-ld: /build/xen/common/event_channel.c:1521: undefined
> reference to `__bitop_bad_size'
> riscv64-linux-gnu-ld: prelink.o: in function `evtchn_init':
> /build/xen/common/event_channel.c:1541: undefined reference to
> `__bitop_bad_size'
> riscv64-linux-gnu-ld: prelink.o: in function `_read_lock':
> /build/xen/./include/xen/rwlock.h:94: undefined reference to
> `__bitop_bad_size'
> riscv64-linux-gnu-ld:
> prelink.o:/build/xen/./arch/riscv/include/asm/atomic.h:195: more
> undefined references to `__bitop_bad_size' follow
> riscv64-linux-gnu-ld: ./.xen-syms.0: hidden symbol `__bitop_bad_size'
> isn't defined
> riscv64-linux-gnu-ld: final link failed: bad value
> make[2]: *** [arch/riscv/Makefile:15: xen-syms] Error 1
> 
> ~ Oleksii