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pkey.7: Add description of signal handling behavior 

The signal behavior of pkeys is special compared to many other
processor and OS features.  Add a special section to describe
the behavior.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
This commit is contained in:
Dave Hansen 2016-10-17 15:07:12 -07:00 committed by Michael Kerrisk
parent 3e712e2a67
commit c92965c2be
1 changed files with 16 additions and 0 deletions
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@ -135,6 +135,22 @@ appropriate for child threads at the time when
.BR clone (2)
is called, or ensure that each child thread can perform its
own initialization of protection key rights.
.SS Signal Handler Behavior
Each time a signal handler is invoked (including nested signals), the
thread is temporarily given a new, default set of protection key rights
that override the rights from the interrupted context.
This means that applications must re-establish their desired protection
key rights upon entering a signal handler if the desired rights differ
from the defaults.
The rights of any interrupted context are restored when the signal
handler returns.
This signal behavior is unusual and is due to the fact that the x86 PKRU
register (which stores protection key access rights) is managed with the
same hardware mechanism (XSAVE) that manages floating-point registers.
The signal behavior is the same as that of floating point registers.
.SS Protection Keys system calls
The Linux kernel implements the following pkey-related system calls:
.BR pkey_mprotect (2),