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SubjectRe: [PATCH 2/7] arm64: Implement copy_thread_tls
[Cc Kees in case he knows something about where arch specific tests live
or whether we have a framework for this]

On Mon, Jan 06, 2020 at 07:03:32PM +0100, Amanieu d'Antras wrote:
> On Mon, Jan 6, 2020 at 6:39 PM Will Deacon <will@kernel.org> wrote:
> > I also ran the native and compat selftests but, unfortunately, they all
> > pass even without this patch. Do you reckon it would be possible to update
> > them to check the tls pointer?
>
> Here's the program I used for testing on arm64. I considered adding it
> to the selftests but there is no portable way of reading the TLS
> register on all architectures.

I'm not saying you need to do this right now.
It feels like we must've run into the "this is architecture
specific"-and-we-want-to-test-this issue before... Do we have a place
where architecture specific selftests live?

>
> #include <sys/syscall.h>
> #include <unistd.h>
> #include <stdio.h>
> #include <stdint.h>
>
> #define __NR_clone3 435
> struct clone_args {
> uint64_t flags;
> uint64_t pidfd;
> uint64_t child_tid;
> uint64_t parent_tid;
> uint64_t exit_signal;
> uint64_t stack;
> uint64_t stack_size;
> uint64_t tls;
> };
>
> #define USE_CLONE3
>
> int main() {
> printf("Before fork: tp = %p\n", __builtin_thread_pointer());
> #ifdef USE_CLONE3
> struct clone_args args = {
> .flags = CLONE_SETTLS,
> .tls = (uint64_t)__builtin_thread_pointer(),
> };
> int ret = syscall(__NR_clone3, &args, sizeof(args));
> #else
> int ret = syscall(__NR_clone, CLONE_SETTLS, 0, 0,
> __builtin_thread_pointer(), 0);
> #endif
> printf("Fork returned %d, tp = %p\n", ret, __builtin_thread_pointer());
> }

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