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Message-ID: <20251012024649.GK1827@brightrain.aerifal.cx>
Date: Sat, 11 Oct 2025 22:46:50 -0400
From: Rich Felker <dalias@...c.org>
To: Alex Rønne Petersen <alex@...xrp.com>
Cc: musl@...ts.openwall.com
Subject: Re: [PATCH] s390x: manually inline __tls_get_addr in
__tls_get_offset
On Fri, Jan 24, 2025 at 06:12:13AM +0100, Alex Rønne Petersen wrote:
> Calling __tls_get_addr with brasl is not valid since it's a global symbol; doing
> so results in an R_390_PC32DBL relocation error from lld. We could fix this by
> marking __tls_get_addr hidden since it is not part of the s390x ABI, or by using
> a different instruction. However, given its simplicity, it makes more sense to
> just manually inline it into __tls_get_offset for performance.
>
> The patch has been tested by applying to Zig's bundled musl copy and running the
> full Zig test suite under qemu-s390x.
> ---
> src/thread/s390x/__tls_get_offset.s | 20 ++++++++++----------
> 1 file changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/src/thread/s390x/__tls_get_offset.s b/src/thread/s390x/__tls_get_offset.s
> index 8ee92de8..405f118b 100644
> --- a/src/thread/s390x/__tls_get_offset.s
> +++ b/src/thread/s390x/__tls_get_offset.s
> @@ -1,17 +1,17 @@
> .global __tls_get_offset
> .type __tls_get_offset,%function
> __tls_get_offset:
> - stmg %r14, %r15, 112(%r15)
> - aghi %r15, -160
> + ear %r0, %a0
> + sllg %r0, %r0, 32
> + ear %r0, %a1
>
> - la %r2, 0(%r2, %r12)
> - brasl %r14, __tls_get_addr
> + la %r1, 0(%r2, %r12)
>
> - ear %r1, %a0
> - sllg %r1, %r1, 32
> - ear %r1, %a1
> + lg %r3, 0(%r1)
> + sllg %r4, %r3, 3
> + lg %r5, 8(%r0)
> + lg %r2, 0(%r4, %r5)
> + ag %r2, 8(%r1)
> + sgr %r2, %r0
>
> - sgr %r2, %r1
> -
> - lmg %r14, %r15, 272(%r15)
> br %r14
> --
> 2.43.0
This must not have been covered by tests because it doesn't work. The
problem is that there is apparently no such thing as 8(%r0); it looks
like r0 is special in addressing and means constant zero. So it should
be fixable just shuffling around which registers are used for what.
I can try to prepare a fix if you don't have time for it.
Rich
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