linux-kernel - Re: [PATCH 1/2] KVM: selftests: Make rseq compatible with glibc-2.35

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Message-ID: <8735e6ncxw.fsf@oldenburg.str.redhat.com>
Date:   Tue, 09 Aug 2022 08:33:31 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     Gavin Shan <gshan@...hat.com>
Cc:     kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        pbonzini@...hat.com, maz@...nel.org, oliver.upton@...ux.dev,
        andrew.jones@...ux.dev, seanjc@...gle.com,
        mathieu.desnoyers@...icios.com, yihyu@...hat.com,
        shan.gavin@...il.com
Subject: Re: [PATCH 1/2] KVM: selftests: Make rseq compatible with glibc-2.35

* Gavin Shan:

> 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).

> @@ -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?

Thanks,
Florian