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tunables: Add LD_HWCAP_MASK to tunables

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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.
This commit is contained in:
Siddhesh Poyarekar 2017-04-17 10:00:35 +05:30
parent 44330b6d32
commit ea9b0ecbf0
4 changed files with 35 additions and 0 deletions
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4
ChangeLog
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@ -1,5 +1,9 @@
2017-06-07 Siddhesh Poyarekar <siddhesh@sourceware.org>
* 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.
* elf/Versions (__tunable_set_val): Rename to __tunable_get_val.
* elf/dl-tunables.c: Likewise.
(do_tunable_update_val): New function.

7
elf/dl-tunables.list
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@ -77,4 +77,11 @@ glibc {
security_level: SXID_IGNORE
}
}
tune {
hwcap_mask {
type: UINT_64
env_alias: LD_HWCAP_MASK
default: HWCAP_IMPORTANT
}
}
}

23
manual/tunables.texi
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@ -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

1
scripts/gen-tunables.awk
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@ -134,6 +134,7 @@ END {
print "# error \"Do not include this file directly.\""
print "# error \"Include tunables.h instead.\""
print "#endif"
print "#include <dl-procinfo.h>\n"
# Now, the enum names
print "\ntypedef enum"