xtensa: add support for call0 ABI in userspace
Provide a Kconfig choice to select whether only the default ABI, only
call0 ABI or both are supported. The default for XEA2 is windowed, but
it may change for XEA3. Call0 only runs userspace with PS.WOE disabled.
Supporting both windowed and call0 ABIs is tricky, as there's no
indication in the ELF binaries which ABI they use. So it is done by
probing: each process is started with PS.WOE disabled, but the handler
of an illegal instruction exception taken with PS.WOE retries faulting
instruction after enabling PS.WOE. It must happen before any signal is
delivered to the process, otherwise it may be delivered incorrectly.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index ebc135b..fb64469 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -385,6 +385,54 @@
If unsure, say N.
+config USER_ABI_CALL0
+ bool
+
+choice
+ prompt "Userspace ABI"
+ default USER_ABI_DEFAULT
+ help
+ Select supported userspace ABI.
+
+ If unsure, choose the default ABI.
+
+config USER_ABI_DEFAULT
+ bool "Default ABI only"
+ help
+ Assume default userspace ABI. For XEA2 cores it is windowed ABI.
+ call0 ABI binaries may be run on such kernel, but signal delivery
+ will not work correctly for them.
+
+config USER_ABI_CALL0_ONLY
+ bool "Call0 ABI only"
+ select USER_ABI_CALL0
+ help
+ Select this option to support only call0 ABI in userspace.
+ Windowed ABI binaries will crash with a segfault caused by
+ an illegal instruction exception on the first 'entry' opcode.
+
+ Choose this option if you're planning to run only user code
+ built with call0 ABI.
+
+config USER_ABI_CALL0_PROBE
+ bool "Support both windowed and call0 ABI by probing"
+ select USER_ABI_CALL0
+ help
+ Select this option to support both windowed and call0 userspace
+ ABIs. When enabled all processes are started with PS.WOE disabled
+ and a fast user exception handler for an illegal instruction is
+ used to turn on PS.WOE bit on the first 'entry' opcode executed by
+ the userspace.
+
+ This option should be enabled for the kernel that must support
+ both call0 and windowed ABIs in userspace at the same time.
+
+ Note that Xtensa ISA does not guarantee that entry opcode will
+ raise an illegal instruction exception on cores with XEA2 when
+ PS.WOE is disabled, check whether the target core supports it.
+
+endchoice
+
endmenu
config XTENSA_CALIBRATE_CCOUNT