This recognizes the DL_CACHE_HWCAP_EXTENSION flag in cache entries,
and picks the supported cache entry with the highest priority.
The elf/tst-glibc-hwcaps-prepend-cache test documents a non-desired
aspect of the current cache implementation: If the cache selects a DSO
that does not exist on disk, _dl_map_object falls back to open_path,
which may or may not find an alternative implementation. This is an
existing limitation that also applies to the legacy hwcaps processing
for ld.so.cache.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
This hacks non-power-set processing into _dl_important_hwcaps.
Once the legacy hwcaps handling goes away, the subdirectory
handling needs to be reworked, but it is premature to do this
while both approaches are still supported.
ld.so supports two new arguments, --glibc-hwcaps-prepend and
--glibc-hwcaps-mask. Each accepts a colon-separated list of
glibc-hwcaps subdirectory names. The prepend option adds additional
subdirectories that are searched first, in the specified order. The
mask option restricts the automatically selected subdirectories to
those listed in the option argument. For example, on systems where
/usr/lib64 is on the library search path,
--glibc-hwcaps-prepend=valgrind:debug causes the dynamic loader to
search the directories /usr/lib64/glibc-hwcaps/valgrind and
/usr/lib64/glibc-hwcaps/debug just before /usr/lib64 is searched.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
This was only ever used for the "nosegneg" flag. This approach for
passing hardware capability information creates a subtle dependency
between the kernel and userspace, and ld.so.cache contents. It seems
inappropriate for toady, where people expect to be able to run
system images which very different kernel versions.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
The glibc.tune namespace is vaguely named since it is a 'tunable', so
give it a more specific name that describes what it refers to. Rename
the tunable namespace to 'cpu' to more accurately reflect what it
encompasses. Also rename glibc.tune.cpu to glibc.cpu.name since
glibc.cpu.cpu is weird.
* NEWS: Mention the change.
* elf/dl-tunables.list: Rename tune namespace to cpu.
* sysdeps/powerpc/dl-tunables.list: Likewise.
* sysdeps/x86/dl-tunables.list: Likewise.
* sysdeps/aarch64/dl-tunables.list: Rename tune.cpu to
cpu.name.
* elf/dl-hwcaps.c (_dl_important_hwcaps): Adjust.
* elf/dl-hwcaps.h (GET_HWCAP_MASK): Likewise.
* manual/README.tunables: Likewise.
* manual/tunables.texi: Likewise.
* sysdeps/powerpc/cpu-features.c: Likewise.
* sysdeps/unix/sysv/linux/aarch64/cpu-features.c
(init_cpu_features): Likewise.
* sysdeps/x86/cpu-features.c: Likewise.
* sysdeps/x86/cpu-features.h: Likewise.
* sysdeps/x86/cpu-tunables.c: Likewise.
* sysdeps/x86_64/Makefile: Likewise.
* sysdeps/x86/dl-cet.c: Likewise.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
A note header has 3 4-bytes fields, followed by note name and note
descriptor. According to gABI, in a note entry, the note name field,
not note name size, is padded for the note descriptor. And the note
descriptor field, not note descriptor size, is padded for the next
note entry. Notes are aligned to 4 bytes in 32-bit objects and 8 bytes
in 64-bit objects.
For all GNU notes, the name is "GNU" which is 4 bytes. They have the
same format in the first 16 bytes in both 32-bit and 64-bit objects.
They differ by note descriptor size and note type. So far, .note.ABI-tag
and .note.gnu.build-id notes are always aligned to 4 bytes. The exsting
codes compute the note size by aligning the note name size and note
descriptor size to 4 bytes. It happens to produce the same value as
the actual note size by luck since the name size is 4 and offset of the
note descriptor is 16. But it will produce the wrong size when note
alignment is 8 bytes in 64-bit objects.
This patch defines ELF_NOTE_DESC_OFFSET and ELF_NOTE_NEXT_OFFSET to
properly compute offsets of note descriptor and next note. It uses
alignment of PT_NOTE segment to support both 4-byte and 8-byte note
alignments in 64-bit objects. To handle PT_NOTE segments with
incorrect alignment, which may lead to an infinite loop, if segment
alignment is less than 4, we treate alignment as 4 bytes since some
note segments have 0 or 1 byte alignment.
[BZ #22370]
* elf/dl-hwcaps.c (ROUND): Removed.
(_dl_important_hwcaps): Replace ROUND with ELF_NOTE_DESC_OFFSET
and ELF_NOTE_NEXT_OFFSET.
* elf/dl-load.c (ROUND): Removed.
(open_verify): Replace ROUND with ELF_NOTE_NEXT_OFFSET.
* elf/readelflib.c (ROUND): Removed.
(process_elf_file): Replace ROUND with ELF_NOTE_NEXT_OFFSET.
* include/elf.h [!_ISOMAC]: Include <libc-pointer-arith.h>.
[!_ISOMAC] (ELF_NOTE_DESC_OFFSET): New.
[!_ISOMAC] (ELF_NOTE_NEXT_OFFSET): Likewise.
Drop _dl_hwcap_mask when building with tunables. This completes the
transition of hwcap_mask reading from _dl_hwcap_mask to tunables.
* elf/dl-hwcaps.h: New file.
* elf/dl-hwcaps.c: Include it.
(_dl_important_hwcaps)[HAVE_TUNABLES]: Read and update
glibc.tune.hwcap_mask.
* elf/dl-cache.c: Include dl-hwcaps.h.
(_dl_load_cache_lookup)[HAVE_TUNABLES]: Read
glibc.tune.hwcap_mask.
* sysdeps/sparc/sparc32/dl-machine.h: Likewise.
* elf/dl-support.c (_dl_hwcap2)[HAVE_TUNABLES]: Drop
_dl_hwcap_mask.
* elf/rtld.c (rtld_global_ro)[HAVE_TUNABLES]: Drop
_dl_hwcap_mask.
(process_envvars)[HAVE_TUNABLES]: Likewise.
* sysdeps/generic/ldsodefs.h (rtld_global_ro)[HAVE_TUNABLES]:
Likewise.
* sysdeps/x86/cpu-features.c (init_cpu_features): Don't
initialize dl_hwcap_mask when tunables are enabled.
In dl-hwcaps.c the comment read that rounding was done
to ElfW(Addr), but it's actually rounded to ElfW(Word).
In ldconfig.c we make each comment a sentence and
mention that the "tls" pseudo-hwcap is just for legacy
installations where TLS was optional.
---
2013-05-22 Carlos O'Donell <carlos@redhat.com>
* elf/ldconfig.c (is_hwcap_platform): Make comments full setences.
(main): Mention "tls" pseudo-hwcap is legacy.
* elf/dl-hwcaps.c (_dl_important_hwcaps): Correct rounding comment.
Loading of the vDSO pseudo-hwcap from the type 2 GNU note is
a rather arcane and poorly documented process. Given that I had
a chance to review this code today I thought I would add all
of the things I had to lookup to verify the validity of the
process.
With a single .note.GNU the vDSO can register up to 64 flags,
though in practice you are limited to 64 - _DL_FIRST_EXTRA
bits which on x86 is 12 bits.
The only use of this that I know of is in the Xen support
in Linux where they use the 1st bit to indicate "nosegneg".
I see "We use bit 1 to avoid bugs in some versions of glibc
when bit 0 is used; the choice is otherwise arbitrary.", but
no reference to a glibc bug anywhere. The code as-is should
support bit zero, so we still have that free for future use.
The kernel, glibc, and ld.so.cache must coordinate to ensure
that bit values don't go too high and are used consistently.
---
2013-05-13 Carlos O'Donell <carlos@redhat.com>
* elf/dl-hwcaps.c (_dl_important_hwcaps): Comment vDSO hwcap loading.
* elf/ldconfig.c (is_hwcap_platform): Comment each hwcap check.
(main): Comment "tls" pseudo-hwcap.
