[PATCH] elf: Re-initialise static TLS after .tdata relocation (BZ 34164)
H.J. Lu
hjl.tools@gmail.com
Tue May 26 22:47:31 GMT 2026
On Wed, May 27, 2026 at 6:39 AM Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 26/05/26 18:36, H.J. Lu wrote:
> > On Wed, May 27, 2026 at 2:52 AM Adhemerval Zanella
> > <adhemerval.zanella@linaro.org> wrote:
> >>
> >> The af34b1376a37fa27e1de9d869ed9493fc569bfa6 changed the .tdata
> >> setup from:
> >>
> >> relocation loop (applies relocations to .tdata in DSO memory)
> >> _dl_allocate_tls_init copies relocated .tdata -> main thread TLS
> >>
> >> to a new order:
> >>
> >> _dl_allocate_tls_init copies unrelocated .tdata -> main thread TLS
> >> relocation loop (relocates .tdata in DSO memory, but the TLS block
> >> has stale copies)
> >>
> >> This broke file-scope thread-local initialised with the address of a
> >> function (for instance the cache structs in libmpfr).
> >
> > This is a regression. Please file a glibc bug report.
>
> I think there is no need to file a bug report, it is a regression for
> an unreleased version and it is really related to BZ#34164.
If it is related to BZ #34164, please update BZ #34164 and mention it
in the commit message.
> >
> >> Fix it by splitting ELF_DYNAMIC_RELOCATE inside
> >> _dl_relocate_object_no_relro into the non-IRELATIVE and IRELATIVE
> >> sub-passes (similar as done on static-pie startup by b75ad99d45b)
> >> and call _dl_init_static_tls between them. By the time the IFUNC
> >> pass fires, .tdata is fully relocated.
> >>
> >> Checked on x86_64-linux-gnu and aarch64-linux-gnu.
> >> ---
> >> elf/Makefile | 3 +++
> >> elf/dl-reloc.c | 24 ++++++++++++++++++--
> >> elf/tst-tls-tdata-reloc-lib.c | 42 +++++++++++++++++++++++++++++++++++
> >> elf/tst-tls-tdata-reloc.c | 32 ++++++++++++++++++++++++++
> >> 4 files changed, 99 insertions(+), 2 deletions(-)
> >> create mode 100644 elf/tst-tls-tdata-reloc-lib.c
> >> create mode 100644 elf/tst-tls-tdata-reloc.c
> >>
> >> diff --git a/elf/Makefile b/elf/Makefile
> >> index d7bab52cd97..a58a902451c 100644
> >> --- a/elf/Makefile
> >> +++ b/elf/Makefile
> >> @@ -1297,6 +1297,7 @@ tests += \
> >> tst-ifunc-resolver-protector \
> >> tst-ifunc-tls-init \
> >> tst-ifunc-tls-write \
> >> + tst-tls-tdata-reloc \
> >> # tests
> >> # Note: sysdeps/x86_64/ifuncmain8.c uses ifuncmain8.
> >> tests-internal += \
> >> @@ -1365,6 +1366,7 @@ modules-names += \
> >> tst-ifunc-tls-init-lib1 \
> >> tst-ifunc-tls-init-lib2 \
> >> tst-ifunc-tls-write-lib \
> >> + tst-tls-tdata-reloc-lib \
> >> # modules-names
> >> ifeq (no,$(with-lld))
> >> modules-names += ifuncmod5
> >> @@ -2518,6 +2520,7 @@ $(objpfx)tst-ifunc-tls-init: $(objpfx)tst-ifunc-tls-init-lib1.so
> >> $(objpfx)tst-ifunc-tls-init.out: \
> >> $(objpfx)tst-ifunc-tls-init-lib2.so
> >> $(objpfx)tst-ifunc-tls-write: $(objpfx)tst-ifunc-tls-write-lib.so
> >> +$(objpfx)tst-tls-tdata-reloc: $(objpfx)tst-tls-tdata-reloc-lib.so
> >>
> >> $(objpfx)tst-unique1.out: $(objpfx)tst-unique1mod1.so \
> >> $(objpfx)tst-unique1mod2.so
> >> diff --git a/elf/dl-reloc.c b/elf/dl-reloc.c
> >> index 91497b38397..15a6a4cffef 100644
> >> --- a/elf/dl-reloc.c
> >> +++ b/elf/dl-reloc.c
> >> @@ -269,9 +269,29 @@ _dl_relocate_object_no_relro (struct link_map *l, struct r_scope_elem *scope[],
> >> }
> >>
> >> {
> >> - /* Do the actual relocation of the object's GOT and other data. */
> >> + /* Do the actual relocation of the object's GOT and other data.
> >>
> >> - ELF_DYNAMIC_RELOCATE (l, scope, lazy, consider_profiling, skip_ifunc);
> >> + Process the non-IRELATIVE pass first so .tdata is fully relocated
> >> + (including R_*_RELATIVE / R_*_64 fixups for TLS initialisers, e.g. a
> >> + file-scope thread-local initialised with the address of a function),
> >> + then refresh the static TLS slot before the IRELATIVE pass runs the
> >> + IFUNC resolvers. Without this, a resolver would see the unrelocated
> >> + initialiser bytes that were placed into the slot by the early
> >> + _dl_allocate_tls_init. */
> >> + ELF_DYNAMIC_RELOCATE_NOIFUNC (l, scope, lazy, consider_profiling);
> >> +
> >> +#ifdef SHARED
> >> + /* Re-initialise the static TLS slot with the .tdata so the IRELATIVE
> >> + pass observes a fully-relocated initialiser image. Skipped for objects
> >> + without static TLS or before the main thread TCB has been set up. */
> >> + if (l->l_tls_blocksize != 0
> >> + && __rtld_tls_init_tp_called
> >> + && l->l_tls_offset != NO_TLS_OFFSET
> >> + && l->l_tls_offset != FORCED_DYNAMIC_TLS_OFFSET)
> >> + _dl_init_static_tls (l);
> >> +#endif
> >> +
> >> + ELF_DYNAMIC_RELOCATE_IFUNC (l, scope, lazy, skip_ifunc);
> >>
> >> if ((consider_profiling || consider_symbind)
> >> && l->l_info[DT_PLTRELSZ] != NULL)
> >> diff --git a/elf/tst-tls-tdata-reloc-lib.c b/elf/tst-tls-tdata-reloc-lib.c
> >> new file mode 100644
> >> index 00000000000..73aa58b0722
> >> --- /dev/null
> >> +++ b/elf/tst-tls-tdata-reloc-lib.c
> >> @@ -0,0 +1,42 @@
> >> +/* Shared library for tst-tls-tdata-reloc.
> >> + Copyright (C) 2026 Free Software Foundation, Inc.
> >> + This file is part of the GNU C Library.
> >> +
> >> + The GNU C Library is free software; you can redistribute it and/or
> >> + modify it under the terms of the GNU Lesser General Public
> >> + License as published by the Free Software Foundation; either
> >> + version 2.1 of the License, or (at your option) any later version.
> >> +
> >> + The GNU C Library is distributed in the hope that it will be useful,
> >> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> >> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> >> + Lesser General Public License for more details.
> >> +
> >> + You should have received a copy of the GNU Lesser General Public
> >> + License along with the GNU C Library; if not, see
> >> + <https://www.gnu.org/licenses/>. */
> >> +
> >> +#define EXPECTED 0x12345678
> >> +
> >> +static int
> >> +callee (void)
> >> +{
> >> + return EXPECTED;
> >> +}
> >> +
> >> +typedef struct
> >> +{
> >> + int (*func) (void);
> >> +} cache_t;
> >> +
> >> +/* General-dynamic TLS: the initialiser of '.func' produces an
> >> + R_*_RELATIVE on .tdata. */
> >> +__thread cache_t cache = { .func = callee };
> >> +
> >> +int
> >> +call_through_tls (void)
> >> +{
> >> + if (cache.func == 0)
> >> + return -1;
> >> + return cache.func ();
> >> +}
> >> diff --git a/elf/tst-tls-tdata-reloc.c b/elf/tst-tls-tdata-reloc.c
> >> new file mode 100644
> >> index 00000000000..1d38726e364
> >> --- /dev/null
> >> +++ b/elf/tst-tls-tdata-reloc.c
> >> @@ -0,0 +1,32 @@
> >> +/* Check that .tdata relocations are applied to the static TLS slot.
> >> + Copyright (C) 2026 Free Software Foundation, Inc.
> >> + This file is part of the GNU C Library.
> >> +
> >> + The GNU C Library is free software; you can redistribute it and/or
> >> + modify it under the terms of the GNU Lesser General Public
> >> + License as published by the Free Software Foundation; either
> >> + version 2.1 of the License, or (at your option) any later version.
> >> +
> >> + The GNU C Library is distributed in the hope that it will be useful,
> >> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> >> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> >> + Lesser General Public License for more details.
> >> +
> >> + You should have received a copy of the GNU Lesser General Public
> >> + License along with the GNU C Library; if not, see
> >> + <https://www.gnu.org/licenses/>. */
> >> +
> >> +#include <support/check.h>
> >> +
> >> +#define EXPECTED 0x12345678
> >> +
> >> +extern int call_through_tls (void);
> >> +
> >> +static int
> >> +do_test (void)
> >> +{
> >> + TEST_COMPARE (call_through_tls (), EXPECTED);
> >> + return 0;
> >> +}
> >> +
> >> +#include <support/test-driver.c>
> >> --
> >> 2.43.0
> >>
> >
> >
>
--
H.J.
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