On 2022-06-25, 罗勇刚(Yonggang Luo) wrote:
On Sat, Jun 25, 2022 at 12:47 PM Markus Wichmann <nullp...@gmx.net> wrote:
On Sat, Jun 25, 2022 at 11:36:09AM +0800, 罗勇刚(Yonggang Luo) wrote:
> So I am confused. What's the situation about ELF-TLS support in musl?
> Is that still broken now?
musl has always supported ELF-TLS anywhere except in libc itself. That
was also never the problem. The problem was that the mesa people select
the initial-exec TLS model explicitly, even though libGL ends up being
dlopen()ed quite often, and then you should be using the general-dynamic
model instead.
My question is does musl support ELS-TLS when using dl-open.
It is supported.
For shared objects using the initial-exec TLS model, they must be at load time
(DT_NEEDED),
not via dlopen.
See https://maskray.me/blog/2021-02-14-all-about-thread-local-storage
for background.
According to [1], Rich proposed dropping the initial-exec attribute and
replacing it with -mtls-dialect=gnu2 eight years ago. Has that happened
yet? If so, dlopen()ing libGL with musl ought to work.
`initial-exec` are only specified for __GLIBC__, If musl not predefined
macro ` __GLIBC__`
```
#if defined(__GLIBC__)
#define __THREAD_INITIAL_EXEC thread_local
__attribute__((tls_model("initial-exec")))
#define REALLY_INITIAL_EXEC
#else
#define __THREAD_INITIAL_EXEC thread_local
#endif
```
On x86, you may enable (currently GCC only) -mtls-dialect=gnu2 to get
performance boost. It's just a tiny bit slower than initial-exec.
I added x86-32 TLSDESC and mixed TLS GD/TLSDESC support to lld 14 after
I saw the -mtls-dialect=gnu2 build system improvement in mesa :)
Ciao,
Markus
[1] https://gitlab.freedesktop.org/mesa/mesa/-/issues/966
--
此致
礼
罗勇刚
Yours
sincerely,
Yonggang Luo
