diff options
| -rw-r--r-- | Documentation/arm64/tagged-pointers.txt | 14 |
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. |