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Date: Thu, 16 May 2019 21:50:43 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] fix tls offsets when p_vaddr%p_align != 0 for
TLS_ABOVE_TP
On Fri, May 17, 2019 at 12:51:18AM +0200, Szabolcs Nagy wrote:
> * Rich Felker <dalias@...c.org> [2019-05-16 09:22:46 -0400]:
> > > i can make the tls_offset fix a separate change from
> > > the p_vaddr%p_align!=0 fix.
> >
> > I'd like that, both because it was non-obvious to me that this was
> > another major change, and because it fixes a separate, major
> > user-facing bug (this is what was breaking rust, and could break lots
> > of other things) rather than the new issue with lld's Bionic hack.
>
> ok
Thanks!
> From 28dd0b581b4d8b0903447b5e169155f11be94cf7 Mon Sep 17 00:00:00 2001
> From: Szabolcs Nagy <nsz@...t70.net>
> Date: Mon, 13 May 2019 18:47:11 +0000
> Subject: [PATCH 2/2] fix tls offsets when p_vaddr%p_align != 0 on TLS_ABOVE_TP
> targets
>
> currently the bfd linker does not seem to create tls segments where
> p_vaddr%p_align != 0, but this is valid in ELF and then the runtime
> computed tls offset must satisfy
>
> offset%p_align == (base+p_vaddr)%p_align
>
> and in case of local exec tls (main executable) the smallest such
> offset must be used (otherwise it is incompatible with the offset
> computed by the static linker). the !TLS_ABOVE_TP case is handled
> correctly (the offset is negative then in the formula).
>
> the ldso code for TLS_ABOVE_TP is changed so the static tls offset
> of each module satisfies the formula.
> ---
> ldso/dynlink.c | 7 ++++---
> src/env/__init_tls.c | 3 ++-
> 2 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/ldso/dynlink.c b/ldso/dynlink.c
> index 566b69e6..f9a7cc06 100644
> --- a/ldso/dynlink.c
> +++ b/ldso/dynlink.c
> @@ -1126,8 +1126,8 @@ static struct dso *load_library(const char *name, struct dso *needed_by)
> p->tls_id = ++tls_cnt;
> tls_align = MAXP2(tls_align, p->tls.align);
> #ifdef TLS_ABOVE_TP
> - p->tls.offset = tls_offset + ( (tls_align-1) &
> - -(tls_offset + (uintptr_t)p->tls.image) );
> + p->tls.offset = tls_offset + ( (p->tls_align-1) &
~~~~~~~~~
This should be tls.align. I can fix it up though when applying.
Rich
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