[PATCH] elf: Re-initialise static TLS after .tdata relocation (BZ 34164)
Adhemerval Zanella Netto
adhemerval.zanella@linaro.org
Tue May 26 22:39:05 GMT 2026
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.
>
>> 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
>>
>
>
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