diff options
| author | Siddhesh Poyarekar <siddhesh@sourceware.org> | 2017-04-17 10:00:35 +0530 |
|---|---|---|
| committer | Siddhesh Poyarekar <siddhesh@sourceware.org> | 2017-06-07 11:11:37 +0530 |
| commit | ea9b0ecbf0e7b6e8281047624efbe1b2cbb6d487 (patch) | |
| tree | 59984b1e6f5bc7e5f66a349e69359fd33090393a /manual | |
| parent | 44330b6d32904fdc8b6835a112e0ba0aee9f4ef3 (diff) | |
tunables: Add LD_HWCAP_MASK to tunables
Add LD_HWCAP_MASK to tunables in preparation of it being removed from
rtld.c. This allows us to read LD_HWCAP_MASK much earlier so that it
can influence IFUNC resolution in aarch64.
This patch does not actually do anything other than read the
LD_HWCAP_MASK variable and add the tunables way to set the
LD_HWCAP_MASK, i.e. via the glibc.tune.hwcap_mask tunable. In a
follow-up patch, the _dl_hwcap_mask will be replaced with
glibc.tune.hwcap_mask to complete the transition.
* elf/dl-tunables.list: Add glibc.tune.hwcap_mask.
* scripts/gen-tunables.awk: Include dl-procinfo.h.
* manual/tunables.texi: Document glibc.tune.hwcap_mask.
Diffstat (limited to 'manual')
| -rw-r--r-- | manual/tunables.texi | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/manual/tunables.texi b/manual/tunables.texi index ac8c38fbde..c9a4cb7fe5 100644 --- a/manual/tunables.texi +++ b/manual/tunables.texi @@ -31,6 +31,8 @@ their own namespace. @menu * Tunable names:: The structure of a tunable name * Memory Allocation Tunables:: Tunables in the memory allocation subsystem +* Hardware Capability Tunables:: Tunables that modify the hardware + capabilities seen by @theglibc{} @end menu @node Tunable names @@ -190,3 +192,24 @@ number of arenas is determined by the number of CPU cores online. For 32-bit systems the limit is twice the number of cores online and on 64-bit systems, it is 8 times the number of cores online. @end deftp + +@node Hardware Capability Tunables +@section Hardware Capability Tunables +@cindex hardware capability tunables +@cindex hwcap tunables +@cindex tunables, hwcap + +@deftp {Tunable namespace} glibc.tune +Behavior of @theglibc{} can be tuned to assume specific hardware capabilities +by setting the following tunables in the @code{tune} namespace: +@end deftp + +@deftp Tunable glibc.tune.hwcap_mask +This tunable supersedes the @env{LD_HWCAP_MASK} environment variable and is +identical in features. + +The @code{AT_HWCAP} key in the Auxilliary Vector specifies instruction set +extensions available in the processor at runtime for some architectures. The +@code{glibc.tune.hwcap_mask} tunable allows the user to mask out those +capabilities at runtime, thus disabling use of those extensions. +@end deftp |