The memory barrier prevents the compiler from changing the program order
of memory accesses in such a way that accesses to the guarded resource
get outside the guarded stage. As cmpxchg() defines the start of the
guarded stage it also represents an effective memory barrier.
On x86, the architecture ensures to not reorder writes with older reads,
writes to memory with other writes (except in cases that are not
relevant for our locks), or read/write instructions with I/O
instructions, locked instructions, and serializing instructions.
However on ARM, the architectural memory model allows not only that
memory accesses take local effect in another order as their program
order but also that different observers (components that can access
memory like data-busses, TLBs and branch predictors) observe these
effects each in another order. Thus, a correct program order isn't
sufficient for a correct observation order. An additional architectural
preservation of the memory barrier is needed to achieve this.
Fixes#692
GCC 4.7.4 and newer seems to optimize the lock-variable accesses more
radically, which uncovered the missing volatile qualifier and resulted
in:
Assertion "(int)locked >= 0" failed in file '.../okl4_x86/kernel/include/kernel/read_write_lock.h', line 151 (fn=f0104771)
--- "KD# assert" ---
Invalidating all branch predictors before switching the PD
fixes instability problems on Panda and has not much effect
on the performance of other boards. However, we neither know why
this is a fix nor wether it fixes the real cause of the problem.
fix#1294
Previously, the timer was used to remember the state of the time slices.
This was sufficient before priorities entered the scene as a thread always
received a fresh time slice when he was scheduled away. However, with
priorities this isn't always the case. A thread can be preempted by another
thread due to a higher priority. In this case the low-priority thread must
remember how much time he has consumed from its current time slice because
the timer gets re-programmed. Otherwise, if we have high-priority threads
that block and unblock with high frequency, the head of the next lower
priority would start with a fresh time slice all the time and is never
superseded.
fix#1287
Some SDL applications expect the SDL_image headers in include/SDL to be
reachable without the SDL/ prefix. This patch adds the corresponding
search path. Furthermore it enables support for XPM images.
Ported drivers list and extract all needed source files. This decouples
ports according to contrib sources and also enables us to revert lxip to
Linux version 3.9, while staying with 3.14 for usb.
Fixes#1285
The manpage to errno tells the following story:
The <errno.h> header file defines the integer variable errno, which is
set by system calls and some library functions in the event of an error
to indicate what went wrong. Its value is significant only when the
return value of the call indicated an error (i.e., -1 from most system
calls; -1 or NULL from most library functions); a function that
succeeds is allowed to change errno.
Valid error numbers are all nonzero; errno is never set to zero by any
system call or library function.
When the 'Mtd::FPU' flag is set during the registration of a
virtualization event handler, it must also be set whenever the event
handler returns.
Fixes#1283
This patch ensures that priority values passed as session arguments
are within the valid range of priorities. Without the clamping, a child
could specify a priority of a lower priority band than the one assigned
to the subsystem. Thanks to Johannes Schlatow for reporting this issue.
Fixes#1279
This is just a quick fix to calm down the buildbot - a revised
implementation is needed according to issue #1277. Further, the reason
for the increased test duration on several platforms must be
investigated.
The alias is rather Linux-specific and also prevents particularly
tailored jiffies implementations. For the existing dde_linux ports (usb
and lxip) we just define jiffies to be dde_kit_timer_ticks with a
preprocessor macro.
The menu view generates a simple dialog of widgets and reports the
hovered element. It is meant to be embedded into applications that
require simple GUIs but don't want to deal with the pecularities of
a full-blown widget set.
The new 'session_control' function can be used to perform operations on
the global view stack that span one or multiple sessions, e.g., bringing
all views of specific sessions to the front, or hiding them.
If the Rom_session::update function returns false, the ROM dataspace may
have been physically destructed (and core has removed all mappings).
In this case, we have to omit the detach operation in the destructor
of 'Attached_dataspace' to avoid detaching the same region twice.
