sandbox: asm: implement setjmp/longjmp/initjmp

To extend incoming bthread support to sandbox, implement setjmp, longjmp
and initjmp. Unlike bare metal platforms, setjmp() and longjmp() are
readily provided on standard-conforming hosted platforms.  initjmp() on
the other hand requires us to be able to invoke a function with a
user-supplied stack pointer, which isn't possible in standard C.

For POSIX systems, there are two methods to portably achieve this though:

  - Use makecontext(2) to set up a new context. makecontext(2) was however
    removed in POSIX.1-2008 and at least GCC 10.2.1 ASan complains that it
    "doesn't fully support makecontext/swapcontext functions and may
    produce false positives in some cases!"

  - Use sigaltstack to set a new signal stack, raise the signal call,
    setjmp in the signal handler to store the new stack pointer, return
    regularly from signal handler and then longjmp back

Both methods are implemented in QEMU. While QEMU uses the makecontext
method by default, for the reasons described, import the second implementation
and use it implement initjmp.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/sandbox/Kconfig b/arch/sandbox/Kconfig
index 1a4e3bacf6..cef8e9fb7a 100644
--- a/arch/sandbox/Kconfig
+++ b/arch/sandbox/Kconfig
@@ -13,6 +13,7 @@ config SANDBOX
 	select PARTITION_DISK
 	select ARCH_HAS_STACK_DUMP if ASAN
 	select GENERIC_FIND_NEXT_BIT
+	select HAS_ARCH_SJLJ
 	default y
 
 config ARCH_TEXT_BASE