mode directories
This commit is 'broken' as it leaves the repository in an unbuildable state.
The purpose of having this commit is so that there is a commit where the
modifications to these files is *just* a rename, making it easier to merge
these changes into other branches.
This commit aims to rationalize how we represent different types
for compatiblity between ARM and x86, as well as between 32 and
64 bit code. The choices being made here is to declare that a
uint32_t has a type of 'int', this allows uint32_t to be declared
consistently across 32 and 64 bit (at least in GCC).
The word_t type is declared using a 'long' (not a uint32_t or uint64_t) to
allow for a word_t to be backed by the same type on both 32 and 64 bit
All other types that want to be declared as the size of a native word
get declared in terms of a word_t
This commit deprecates seL4_ReplyWait, removes seL4_NBwait completely,
and changes the return type of seL4_Wait to void (seL4_Wait should be
used for notification objects, and seL4_Recv should be used where
seL4_Wait was used previously for endpoints).
Use of these abstractions aids compiler portability, as only a single place in
the kernel needs to be adapted. This commit is not intended to affect either
verification or generated code.
The previous definition of TCB_NAME_LENGTH assumed that the TCB was
split evenly into the cnode region and the rest. It did this by
calculating the size of the rest by using the size of the cnode
region. In actual fact the cnode region might be smaller, making
the size of the rest the size of the total tcb block size, minus
the cnode size. The max name length is therefore this region, minus
the size of the tcb_t
Configuring standalone kernel builds (such as those used by verification)
has been done in a completely different way to how the kernel is
configured for project builds. As the kernel gains additional options
it becomes difficult to maintain standalone kernel builds without
tediously exporting these additional options, such tedious work is
what autoconf.h is meant to address
The new configuration strategy requires a include/plat/PLAT/autoconf.h
file to exist for any platform that wants to hae standalone builds
performed on it. This configuration also becomes the *verified*
configuration, and makes it clear for projects to build the kernel
in the verified configuration.
Create new function "clz" which invokes __builtin_clz
Tell the C parser to not try translate it (DONT_TRANSLATE), but instead
to trust the spec we provide (FNSPEC+MODIFIES).
Squashed the fix by Anna Lyons:
rearrange CLZ in util.h and s/__builtin__clz/__builtin_clz/
Background
seL4 organizes threads into ready queues, of which there is one for each
domain, for each priority level. The ready queue for a given
domain/priority combination can be found by indexing the array
`ksReadyQueues` with "domain*num_priorities + priority".
Current scheduler implementation
To find the non-empty ready queue with the maximum priority for the current domain,
seL4 iterates through `ksReadyQueues`, starting with the element
corresponding to the current domain and maximum possible priority, and
decrementing the priority until a non-empty queue is found. This is
problematic in cases where the only ready threads have low priorities,
as iterating through many elements of an array effectively flushes the
cache.
Changes in this patch
This patch replaces the iteration with a lookup into a table of
bitfields per domain. Using bitfields allows the kernel to determine the
highest priority level with a non-empty ready queue for the current
domain by counting the leading zeroes in bitfields. This removes the
negative cache effects of iterating through an array.
Implementation details
For each domain, a multilevel table of bitfields is maintained which
stores the priority levels within that domain for which there exist
ready threads. On a 32-bit architecture, the top level of the table is a 32-bit bitfield where if
the ith bit is set, there is at least 1 priority level in
[i*32..i*32+31] with a non-empty ready queue. The positions of bits in
this bitfield are used as indices into the second level table, which is
an array of 32-bit bitfields. The ith bit of the jth bitfield in this
array set to 1, indicates that priority level j*32+i has a non-empty
ready queue.
