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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
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.
-rw-r--r--ChangeLog4
-rw-r--r--elf/dl-tunables.list7
-rw-r--r--manual/tunables.texi23
-rw-r--r--scripts/gen-tunables.awk1
4 files changed, 35 insertions, 0 deletions
diff --git a/ChangeLog b/ChangeLog
index b85c6182ff..7a42c78932 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -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.
diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list
index b9f1488798..41ce9afa28 100644
--- a/elf/dl-tunables.list
+++ b/elf/dl-tunables.list
@@ -77,4 +77,11 @@ glibc {
security_level: SXID_IGNORE
}
}
+ tune {
+ hwcap_mask {
+ type: UINT_64
+ env_alias: LD_HWCAP_MASK
+ default: HWCAP_IMPORTANT
+ }
+ }
}
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
diff --git a/scripts/gen-tunables.awk b/scripts/gen-tunables.awk
index b10b00ebd6..93e5aff0ef 100644
--- a/scripts/gen-tunables.awk
+++ b/scripts/gen-tunables.awk
@@ -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"