xtensa: support call0 ABI

Most changes are mechanical replacement of 'retw' instruction with
'abi_ret' macro, defined to 'retw' or 'ret' according to ABI.
Assembly code that makes calls is duplicated for call0 ABI with changed
register numbers for parameters/return value and call instruction.
'entry' instructions are replaced with 'abi_entry' macro.

More interesting changes:
- non-leaf assembly functions (e.g. _dl_tlsdesc_dynamic,
  _dl_linux_resolve, SYSCALL_ERROR_HANDLER, PSEUDO) now need to preserve
  registers around intermediate calls they make, use temporary stack
  frame for that;
- setjmp/longjmp only need to save and restore return address, stack
  pointer and callee-saved registers in the jmpbuf;
- __clone and syscall functions had hardcoded offsets to parameter
  passed on stack, on call0 ABI they don't need stack frame, so the
  offset is different. Replace these offsets with FRAMESIZE macro.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/libc/sysdeps/linux/xtensa/vfork.S b/libc/sysdeps/linux/xtensa/vfork.S
index 6aced0a50..b8db5c1a1 100644
--- a/libc/sysdeps/linux/xtensa/vfork.S
+++ b/libc/sysdeps/linux/xtensa/vfork.S
@@ -51,6 +51,8 @@
 
 
 HIDDEN_ENTRY (__vfork)
+
+#if defined(__XTENSA_WINDOWED_ABI__)
         .literal .Ljumptable, 0, .L4, .L8, .L12
 
 	mov	a3, a0			# move return address out of the way
@@ -163,6 +165,27 @@ HIDDEN_ENTRY (__vfork)
 	PSEUDO_END (__vfork)
 .Lpseudo_end:
 	retw
+#elif defined(__XTENSA_CALL0_ABI__)
+	SAVE_PID(a5, a8, a3, a4)
+
+	/* Use syscall 'clone'.  Set new stack pointer to the same address.  */
+	movi	a2, SYS_ify (clone)
+	movi	a3, 0
+	movi	a6, CLONE_VM | CLONE_VFORK | SIGCHLD
+	syscall
+
+	RESTORE_PID(a5, a8, a2)
+
+	movi	a3, -4096
+	bgeu	a2, a3, 1f
+	ret
+1:
+	PSEUDO_END (__vfork)
+.Lpseudo_end:
+	ret
+#else
+#error Unsupported Xtensa ABI
+#endif
 
 weak_alias (__vfork, vfork)
 libc_hidden_def(vfork)