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authorLinus Torvalds <torvalds@linux-foundation.org>2013-09-20 17:18:51 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2013-09-20 17:18:51 +0400
commitdcb30e659287a6b40dafed1362532da42ec27229 (patch)
treeb5f74a4b605c59bcef144cbe248879b00e99690c /Documentation
parent7b9e3a6ac00be4f3d654a711573b1794b046c22f (diff)
parent25804e6a96681d5d2142058948e218999e4f547c (diff)
downloadlinux-dcb30e659287a6b40dafed1362532da42ec27229.tar.xz
Merge tag 'arm64-stable' of git://git.kernel.org/pub/scm/linux/kernel/git/cmarinas/linux-aarch64
Pull ARM64 fixes from Catalin Marinas: - Compat register fault reporting fix - Documentation clarification on tagged pointers - hwcap widened to 64-bit (user space already reading it as 64-bit) * tag 'arm64-stable' of git://git.kernel.org/pub/scm/linux/kernel/git/cmarinas/linux-aarch64: arm64: Widen hwcap to be 64 bit arm64: Correctly report LR and SP for compat tasks arm64: documentation: tighten up tagged pointer documentation arm64: Make do_bad_area() function static
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/arm64/tagged-pointers.txt14
1 files changed, 7 insertions, 7 deletions
diff --git a/Documentation/arm64/tagged-pointers.txt b/Documentation/arm64/tagged-pointers.txt
index 264e9841563a..d9995f1f51b3 100644
--- a/Documentation/arm64/tagged-pointers.txt
+++ b/Documentation/arm64/tagged-pointers.txt
@@ -18,17 +18,17 @@ this byte for application use, with the following caveats:
parameters containing user virtual addresses *must* have
their top byte cleared before trapping to the kernel.
- (2) Tags are not guaranteed to be preserved when delivering
- signals. This means that signal handlers in applications
- making use of tags cannot rely on the tag information for
- user virtual addresses being maintained for fields inside
- siginfo_t. One exception to this rule is for signals raised
- in response to debug exceptions, where the tag information
+ (2) Non-zero tags are not preserved when delivering signals.
+ This means that signal handlers in applications making use
+ of tags cannot rely on the tag information for user virtual
+ addresses being maintained for fields inside siginfo_t.
+ One exception to this rule is for signals raised in response
+ to watchpoint debug exceptions, where the tag information
will be preserved.
(3) Special care should be taken when using tagged pointers,
since it is likely that C compilers will not hazard two
- addresses differing only in the upper bits.
+ virtual addresses differing only in the upper byte.
The architecture prevents the use of a tagged PC, so the upper byte will
be set to a sign-extension of bit 55 on exception return.