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SubjectRe: [PATCH 1/2] KVM: selftests: Make rseq compatible with glibc-2.35
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Hi Florian,

On 8/9/22 4:33 PM, Florian Weimer wrote:
>> diff --git a/tools/testing/selftests/kvm/rseq_test.c b/tools/testing/selftests/kvm/rseq_test.c
>> index a54d4d05a058..acb1bf1f06b3 100644
>> --- a/tools/testing/selftests/kvm/rseq_test.c
>> +++ b/tools/testing/selftests/kvm/rseq_test.c
>> @@ -9,6 +9,7 @@
>> #include <string.h>
>> #include <signal.h>
>> #include <syscall.h>
>> +#include <dlfcn.h>
>> #include <sys/ioctl.h>
>> #include <sys/sysinfo.h>
>> #include <asm/barrier.h>
>
> I'm surprised that there isn't a Makefile update to link with -ldl
> (still required for glibc 2.33 and earlier).
>

In next revision, I will add '-ldl' into tools/testing/selftests/kvm/Makefile.


>> @@ -36,6 +37,8 @@ static __thread volatile struct rseq __rseq = {
>> */
>> #define NR_TASK_MIGRATIONS 100000
>>
>> +static bool __rseq_ownership;
>> +static volatile struct rseq *__rseq_info;
>> static pthread_t migration_thread;
>> static cpu_set_t possible_mask;
>> static int min_cpu, max_cpu;
>> @@ -49,11 +52,33 @@ static void guest_code(void)
>> GUEST_SYNC(0);
>> }
>>
>> +static void sys_rseq_ownership(void)
>> +{
>> + long *offset;
>> + unsigned int *size, *flags;
>> +
>> + offset = dlsym(RTLD_NEXT, "__rseq_offset");
>> + size = dlsym(RTLD_NEXT, "__rseq_size");
>> + flags = dlsym(RTLD_NEXT, "__rseq_flags");
>> +
>> + if (offset && size && *size && flags) {
>> + __rseq_ownership = false;
>> + __rseq_info = (struct rseq *)((uintptr_t)__builtin_thread_pointer() +
>> + *offset);
>
> __builtin_thread_pointer doesn't work on all architectures/GCC versions.
> Is this a problem for selftests?
>

It's a problem as the test case is running on all architectures. I think I
need introduce our own __builtin_thread_pointer() for where it's not
supported: (1) PowerPC (2) x86 without GCC 11

Please let me know if I still have missed cases where __buitin_thread_pointer()
isn't supported?

Thanks,
Gavin

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