The way Cortex processors handle exceptions allows writing exception
routines directly in C, as return from exception is handled by providing
a special value for the link register.
However, it is not safe to do this when doing context switching. In
particular, C handlers may push some general-purpose registers that
are used by the handler and pop them later, even when context switch
has happened in the meantime. While the processor will restore {r0-r3}
from the stack when returning from an exception, the C handler code
may push, use and pop another register, such as r4.
It turns out that GCC 4.8 would generally only use r3 in svc_handler and
pendsv_handler, but newer versions tend to use r4, thus clobbering r4
that was restored from the context switch and leading up to a fault
when r4 is used by the task code.
An occurrence of this behaviour takes place with GCC > 4.8 in __wait_evt,
where "me" is stored in r4, which gets clobbered after an exception
triggers pendsv_handler. The exception handler uses r4 internally, does
a context switch and then restores the previous value of r4, which is
not restored by the processor's internal, thus clobbering r4.
This ends up with the following assertion failure:
'tskid < TASK_ID_COUNT' in timer_cancel() at common/timer.c:137
For this reason, it is safer to have assembly routines for exception
handlers that do context switching.
BUG=chromium:631514
BRANCH=None
TEST=Build and run speedy EC with a recent GCC version
Change-Id: Ib068bc12ce2204aee3e0f563efcb94f15aa87013
Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Reviewed-on: https://chromium-review.googlesource.com/362830
Commit-Ready: Shawn N <shawnn@chromium.org>
Tested-by: Shawn N <shawnn@chromium.org>
Reviewed-by: Shawn N <shawnn@chromium.org>
Until HOOK_INIT has completed, do not allow any tasks other than HOOKS
or IDLE to be scheduled. Programmers often make the assumption that
a HOOK_INIT function is guaranteed to be run before task code that depends
on it, so let's make it so.
BUG=chromium:649398
BRANCH=None
TEST=Manual on kevin, compare boot without patch:
...
[0.004 power state 0 = G3, in 0x0008] <-- from chipset task
RTC: 0x00000000 (0.00 s)
[0.004 power state 4 = G3->S5, in 0x0008]
RTC: 0x00000000 (0.00 s)
[0.005 clear MKBP fifo]
[0.006 clear MKBP fifo]
[0.006 KB init state: ... <-- from keyscan task
[0.012 SW 0x05]
[0.155 hash start 0x00020000 0x00019a38]
[0.158 HOOK_INIT DONE!]
... to boot with patch:
...
RTC: 0x58cc614c (1489789260.00 s)
[0.004 clear MKBP fifo]
[0.005 clear MKBP fifo]
[0.010 SW 0x05]
[0.155 hash start 0x00020000 0x000198e0]
[0.157 HOOK_INIT DONE!]
...
Also, verify kevin boots to OS and is generally functional through
sysjump and basic tasks, and verify elm (stm32f0 / cortex-m0) boots.
Change-Id: If56fab05ce9b9650feb93c5cfc2d084aa281e622
Signed-off-by: Shawn Nematbakhsh <shawnn@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/456628
Commit-Ready: Shawn N <shawnn@chromium.org>
Tested-by: Shawn N <shawnn@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
