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authorSiddhesh Poyarekar <siddhesh@sourceware.org>2017-04-17 10:00:35 +0530
committerSiddhesh Poyarekar <siddhesh@sourceware.org>2017-06-07 11:11:37 +0530
commitea9b0ecbf0e7b6e8281047624efbe1b2cbb6d487 (patch)
tree59984b1e6f5bc7e5f66a349e69359fd33090393a /manual
parent44330b6d32904fdc8b6835a112e0ba0aee9f4ef3 (diff)
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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.texi23
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