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, 9 insertions, 0 deletions

diff --git a/libc/sysdeps/linux/xtensa/bits/setjmp.h b/libc/sysdeps/linux/xtensa/bits/setjmp.h
index 183fa3e64..5d3e5509e 100644
--- a/libc/sysdeps/linux/xtensa/bits/setjmp.h
+++ b/libc/sysdeps/linux/xtensa/bits/setjmp.h
@@ -23,6 +23,7 @@
 # error "Never include <bits/setjmp.h> directly; use <setjmp.h> instead."
 #endif
 
+#if defined(__XTENSA_WINDOWED_ABI__)
 /* The jmp_buf structure for Xtensa holds the following (where "proc"
    is the procedure that calls setjmp): 4-12 registers from the window
    of proc, the 4 words from the save area at proc's $sp (in case a
@@ -30,5 +31,13 @@
    proc.  Everything else is saved on the stack in the normal save areas.  */
 
 typedef int __jmp_buf[17];
+#elif defined(__XTENSA_CALL0_ABI__)
+/* The jmp_buf structure for Xtensa Call0 ABI holds the return address,
+   the stack pointer and callee-saved registers (a12 - a15).  */
+
+typedef int __jmp_buf[6];
+#else
+#error Unsupported Xtensa ABI
+#endif
 
 #endif	/* bits/setjmp.h */