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>

18 files changed, 221 insertions, 48 deletions

diff --git a/libc/string/xtensa/memcpy.S b/libc/string/xtensa/memcpy.S
index 2b23b4113..244205611 100644
--- a/libc/string/xtensa/memcpy.S
+++ b/libc/string/xtensa/memcpy.S
@@ -91,7 +91,7 @@ __memcpy_aux:
 #if !XCHAL_HAVE_LOOPS
 	blt	a3, a7, 1b
 #endif
-2:	retw
+2:	abi_ret
 
 
 /* Destination is unaligned.  */
@@ -181,7 +181,7 @@ ENTRY (memcpy)
 3:	bbsi.l	a4, 2, 4f
 	bbsi.l	a4, 1, 5f
 	bbsi.l	a4, 0, 6f
-	retw
+	abi_ret
 
 	/* Copy 4 bytes.  */
 4:	l32i	a6, a3, 0
@@ -190,7 +190,7 @@ ENTRY (memcpy)
 	addi	a5, a5, 4
 	bbsi.l	a4, 1, 5f
 	bbsi.l	a4, 0, 6f
-	retw
+	abi_ret
 
 	/* Copy 2 bytes.  */
 5:	l16ui	a6, a3, 0
@@ -198,14 +198,14 @@ ENTRY (memcpy)
 	s16i	a6, a5, 0
 	addi	a5, a5, 2
 	bbsi.l	a4, 0, 6f
-	retw
+	abi_ret
 
 	/* Copy 1 byte.  */
 6:	l8ui	a6, a3, 0
 	s8i	a6, a5, 0
 
 .Ldone:
-	retw
+	abi_ret
 
 
 /* Destination is aligned; source is unaligned.  */
@@ -276,7 +276,7 @@ ENTRY (memcpy)
 #endif
 	bbsi.l	a4, 1, 5f
 	bbsi.l	a4, 0, 6f
-	retw
+	abi_ret
 
 	/* Copy 2 bytes.  */
 5:	l8ui	a6, a3, 0
@@ -286,11 +286,11 @@ ENTRY (memcpy)
 	s8i	a7, a5, 1
 	addi	a5, a5, 2
 	bbsi.l	a4, 0, 6f
-	retw
+	abi_ret
 
 	/* Copy 1 byte.  */
 6:	l8ui	a6, a3, 0
 	s8i	a6, a5, 0
-	retw
+	abi_ret
 
 libc_hidden_def (memcpy)
diff --git a/libc/string/xtensa/memset.S b/libc/string/xtensa/memset.S
index 435d6dea0..20bf14c75 100644
--- a/libc/string/xtensa/memset.S
+++ b/libc/string/xtensa/memset.S
@@ -63,7 +63,7 @@ __memset_aux:
 #if !XCHAL_HAVE_LOOPS
 	blt	a5, a6, 1b
 #endif
-2:	retw
+2:	abi_ret
 
 
 /* Destination is unaligned.  */
@@ -159,6 +159,6 @@ ENTRY (memset)
 
 	/* Set 1 byte.  */
 	s8i	a3, a5, 0
-6:	retw
+6:	abi_ret
 
 libc_hidden_def (memset)
diff --git a/libc/string/xtensa/strcmp.S b/libc/string/xtensa/strcmp.S
index 8ed1ed009..2dce590db 100644
--- a/libc/string/xtensa/strcmp.S
+++ b/libc/string/xtensa/strcmp.S
@@ -108,7 +108,7 @@ ENTRY (strcmp)
 #endif
 .Lretdiff:
 	sub	a2, a8, a9
-	retw
+	abi_ret
 
 /* s1 is word-aligned; s2 is word-aligned.
 
@@ -229,7 +229,7 @@ ENTRY (strcmp)
 
 	/* Words are equal; some byte is zero.  */
 .Leq:	movi	a2, 0		/* return equal */
-	retw
+	abi_ret
 
 .Lwne2:	/* Words are not equal.  On big-endian processors, if none of the
 	   bytes are zero, the return value can be determined by a simple
@@ -239,10 +239,10 @@ ENTRY (strcmp)
 	bnall	a10, a7, .Lsomezero
 	bgeu	a8, a9, .Lposreturn
 	movi	a2, -1
-	retw
+	abi_ret
 .Lposreturn:
 	movi	a2, 1
-	retw
+	abi_ret
 .Lsomezero:	/* There is probably some zero byte. */
 #endif /* __XTENSA_EB__ */
 .Lwne:	/* Words are not equal.  */
@@ -263,14 +263,14 @@ ENTRY (strcmp)
 	   byte.  Just subtract words to get the return value.
 	   The high order equal bytes cancel, leaving room for the sign.  */
 	sub	a2, a8, a9
-	retw
+	abi_ret
 
 .Ldiff0:
 	/* Need to make room for the sign, so can't subtract whole words.  */
 	extui	a10, a8, 24, 8
 	extui	a11, a9, 24, 8
 	sub	a2, a10, a11
-	retw
+	abi_ret
 
 #else /* !__XTENSA_EB__ */
 	/* Little-endian is a little more difficult because can't subtract
@@ -281,28 +281,28 @@ ENTRY (strcmp)
 	extui	a10, a8, 24, 8
 	extui	a11, a9, 24, 8
 	sub	a2, a10, a11
-	retw
+	abi_ret
 
 .Ldiff0:
 	/* Byte 0 is different.  */
 	extui	a10, a8, 0, 8
 	extui	a11, a9, 0, 8
 	sub	a2, a10, a11
-	retw
+	abi_ret
 
 .Ldiff1:
 	/* Byte 0 is equal; byte 1 is different.  */
 	extui	a10, a8, 8, 8
 	extui	a11, a9, 8, 8
 	sub	a2, a10, a11
-	retw
+	abi_ret
 
 .Ldiff2:
 	/* Bytes 0-1 are equal; byte 2 is different.  */
 	extui	a10, a8, 16, 8
 	extui	a11, a9, 16, 8
 	sub	a2, a10, a11
-	retw
+	abi_ret
 
 #endif /* !__XTENSA_EB */
 
diff --git a/libc/string/xtensa/strcpy.S b/libc/string/xtensa/strcpy.S
index f9f586896..9f42b34e6 100644
--- a/libc/string/xtensa/strcpy.S
+++ b/libc/string/xtensa/strcpy.S
@@ -68,7 +68,7 @@ ENTRY (strcpy)
 	s8i	a8, a10, 1	/* store byte 0 */
 	addi	a10, a10, 2	/* advance dst pointer */
 	bnez	a8, .Lsrcaligned
-1:	retw
+1:	abi_ret
 
 
 /* dst is word-aligned; src is word-aligned.  */
@@ -102,21 +102,21 @@ ENTRY (strcpy)
 #endif /* !XCHAL_HAVE_LOOPS */
 
 .Lz3:	/* Byte 3 is zero.  */
-	retw
+	abi_ret
 
 .Lz0:	/* Byte 0 is zero.  */
 #ifdef __XTENSA_EB__
 	movi	a8, 0
 #endif
 	s8i	a8, a10, 0
-	retw
+	abi_ret
 
 .Lz1:	/* Byte 1 is zero.  */
 #ifdef __XTENSA_EB__
         extui   a8, a8, 16, 16
 #endif
 	s16i	a8, a10, 0
-	retw
+	abi_ret
 
 .Lz2:	/* Byte 2 is zero.  */
 #ifdef __XTENSA_EB__
@@ -125,7 +125,7 @@ ENTRY (strcpy)
 	s16i	a8, a10, 0
 	movi	a8, 0
 	s8i	a8, a10, 2
-	retw
+	abi_ret
 
 	.align	4
 	/* (2 mod 4) alignment for loop instruction */
@@ -144,6 +144,6 @@ ENTRY (strcpy)
 #else
 	bnez	a8, 1b
 #endif
-2:	retw
+2:	abi_ret
 
 libc_hidden_def (strcpy)
diff --git a/libc/string/xtensa/strlen.S b/libc/string/xtensa/strlen.S
index 86fe11390..e1c98c8f0 100644
--- a/libc/string/xtensa/strlen.S
+++ b/libc/string/xtensa/strlen.S
@@ -59,7 +59,7 @@ ENTRY (strlen)
 	/* Byte 3 is zero.  */
 	addi	a3, a3, 3	/* point to zero byte */
 	sub	a2, a3, a2	/* subtract to get length */
-	retw
+	abi_ret
 
 
 /* String is word-aligned.  */
@@ -88,16 +88,16 @@ ENTRY (strlen)
 
 .Lz0:	/* Byte 0 is zero.  */
 	sub	a2, a3, a2	/* subtract to get length */
-	retw
+	abi_ret
 
 .Lz1:	/* Byte 1 is zero.  */
 	addi	a3, a3, 1	/* point to zero byte */
 	sub	a2, a3, a2	/* subtract to get length */
-	retw
+	abi_ret
 
 .Lz2:	/* Byte 2 is zero.  */
 	addi	a3, a3, 2	/* point to zero byte */
 	sub	a2, a3, a2	/* subtract to get length */
-	retw
+	abi_ret
 
 libc_hidden_def (strlen)
diff --git a/libc/string/xtensa/strncpy.S b/libc/string/xtensa/strncpy.S
index 115d44cf8..aa8db5da1 100644
--- a/libc/string/xtensa/strncpy.S
+++ b/libc/string/xtensa/strncpy.S
@@ -67,7 +67,7 @@ __strncpy_aux:
 	j	.Lfill
 
 .Lret:
-	retw
+	abi_ret
 
 
 ENTRY (strncpy)
@@ -129,7 +129,7 @@ ENTRY (strncpy)
 	addi	a10, a10, 1
 	bnez    a4, .Lfillcleanup
 
-2:	retw
+2:	abi_ret
 
 .Lfill1mod2: /* dst address is odd */
 	s8i	a9, a10, 0	/* store byte 0 */
@@ -235,6 +235,6 @@ ENTRY (strncpy)
 #endif
 2:	j	.Lfill
 
-3:	retw
+3:	abi_ret
 
 libc_hidden_def (strncpy)
diff --git a/libc/sysdeps/linux/xtensa/__longjmp.S b/libc/sysdeps/linux/xtensa/__longjmp.S
index 4d55906db..acc0b4ff2 100644
--- a/libc/sysdeps/linux/xtensa/__longjmp.S
+++ b/libc/sysdeps/linux/xtensa/__longjmp.S
@@ -48,6 +48,7 @@
 
 ENTRY (__longjmp)
 
+#if defined(__XTENSA_WINDOWED_ABI__)
 	/* Invalidate all but the current window.  Reading and writing
 	   special registers WINDOWBASE and WINDOWSTART are
 	   privileged operations, so user processes must call the
@@ -120,6 +121,22 @@ ENTRY (__longjmp)
 	movnez	a2, a3, a3
 
 	retw
+#elif defined(__XTENSA_CALL0_ABI__)
+	l32i	a0, a2, 0
+	l32i	a1, a2, 4
+	l32i	a12, a2, 8
+	l32i	a13, a2, 12
+	l32i	a14, a2, 16
+	l32i	a15, a2, 20
+
+	/* Return v ? v : 1.  */
+	movi	a2, 1
+	movnez	a2, a3, a3
+
+	ret
+#else
+#error Unsupported Xtensa ABI
+#endif
 END (__longjmp)
 
 libc_hidden_def (__longjmp)
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 */
diff --git a/libc/sysdeps/linux/xtensa/clone.S b/libc/sysdeps/linux/xtensa/clone.S
index 34d68a875..88cd6c1c3 100644
--- a/libc/sysdeps/linux/xtensa/clone.S
+++ b/libc/sysdeps/linux/xtensa/clone.S
@@ -51,7 +51,7 @@ ENTRY (__clone)
 	mov	a8, a6			/* use a8 as a temp */
 	mov	a6, a4
 	mov	a4, a8
-	l32i	a8, a1, 16		/* child_tid */
+	l32i	a8, a1, FRAMESIZE	/* child_tid */
 	movi	a2, SYS_ify(clone)
 
 	/* syscall(NR_clone,clone_flags, usp, parent_tid, child_tls, child_tid)
@@ -65,7 +65,7 @@ ENTRY (__clone)
 	/* fall through for parent */
 
 .Lpseudo_end:
-	retw
+	abi_ret
 
 .Leinval:
 	movi	a2, -EINVAL
@@ -94,17 +94,26 @@ ENTRY (__clone)
 
 	/* start child thread */
 	movi	a0, 0			/* terminate the stack frame */
+
+#if defined(__XTENSA_WINDOWED_ABI__)
 	mov	a6, a9			/* load up the 'arg' parameter */
 	callx4	a7			/* call the user's function */
 
 	/* Call _exit.  Note that any return parameter from the user's
 	   function in a6 is seen as inputs to _exit. */
-#ifdef	PIC
-	movi	a2, _exit@PLT
+	movi	a2, JUMPTARGET(_exit)
+	callx4	a2
+#elif defined(__XTENSA_CALL0_ABI__)
+	mov	a2, a9			/* load up the 'arg' parameter */
+	callx0	a7			/* call the user's function */
+
+	/* Call _exit.  Note that any return parameter from the user's
+	   function in a2 is seen as inputs to _exit.  */
+	movi	a0, JUMPTARGET(_exit)
+	callx0	a0
 #else
-	movi	a2, _exit
+#error Unsupported Xtensa ABI
 #endif
-	callx4	a2
 
 PSEUDO_END (__clone)
 
diff --git a/libc/sysdeps/linux/xtensa/crt1.S b/libc/sysdeps/linux/xtensa/crt1.S
index 025ebd070..efbe264c0 100644
--- a/libc/sysdeps/linux/xtensa/crt1.S
+++ b/libc/sysdeps/linux/xtensa/crt1.S
@@ -76,6 +76,7 @@
 	.global	_start
 	.type	_start, @function
 _start:
+#if defined(__XTENSA_WINDOWED_ABI__)
 	/* Clear a0 to obviously mark the outermost frame.  */
 	movi	a0, 0
 
@@ -104,6 +105,35 @@ _start:
 	   But let the libc call main.    */
 	movi	a4, __uClibc_main
 	callx4	a4
+#elif defined(__XTENSA_CALL0_ABI__)
+	/* Setup the shared library termination function.  */
+	mov	a7, a2
+
+	/* Load up the user's main function.  */
+	movi	a2, main
+
+	/* Extract the arguments as encoded on the stack and set up
+	   the arguments for `main': argc, argv.  envp will be determined
+	   later in __uClibc_main.  */
+	l32i	a3, a1, 0	/* Load the argument count.  */
+	addi	a4, a1, 4	/* Compute the argv pointer.  */
+
+	/* Push address of our own entry points to .fini and .init.  */
+	movi	a5, _init
+	movi	a6, _fini
+
+	/* Provide the highest stack address to the user code (for stacks
+	   which grow downwards).  Note that we destroy the stack version
+	   of argc here.  */
+	s32i	a1, a1, 0
+
+	/* Call the user's main function, and exit with its value.
+	   But let the libc call main.    */
+	movi	a0, __uClibc_main
+	callx0	a0
+#else
+#error Unsupported Xtensa ABI
+#endif
 
 	/* Crash if somehow `exit' does return.  */
 	ill
diff --git a/libc/sysdeps/linux/xtensa/crti.S b/libc/sysdeps/linux/xtensa/crti.S
index a01c02c9f..ba804eb45 100644
--- a/libc/sysdeps/linux/xtensa/crti.S
+++ b/libc/sysdeps/linux/xtensa/crti.S
@@ -5,12 +5,25 @@
 	.global	_init
 	.type	_init, @function
 _init:
+#if defined(__XTENSA_WINDOWED_ABI__)
 	entry	sp, 48
-
+#elif defined(__XTENSA_CALL0_ABI__)
+	addi	sp, sp, -16
+	s32i	a0, sp, 0
+#else
+#error Unsupported Xtensa ABI
+#endif
 
 	.section .fini
 	.align	4
 	.global	_fini
 	.type	_fini, @function
 _fini:
+#if defined(__XTENSA_WINDOWED_ABI__)
 	entry	sp, 48
+#elif defined(__XTENSA_CALL0_ABI__)
+	addi	sp, sp, -16
+	s32i	a0, sp, 0
+#else
+#error Unsupported Xtensa ABI
+#endif
diff --git a/libc/sysdeps/linux/xtensa/crtn.S b/libc/sysdeps/linux/xtensa/crtn.S
index ab1a489c5..a3598da1a 100644
--- a/libc/sysdeps/linux/xtensa/crtn.S
+++ b/libc/sysdeps/linux/xtensa/crtn.S
@@ -1,8 +1,23 @@
 /* glibc's sysdeps/xtensa/elf/initfini.c used for reference [EPILOG] */
 
 	.section .init
+#if defined(__XTENSA_WINDOWED_ABI__)
 	retw
-
+#elif defined(__XTENSA_CALL0_ABI__)
+	l32i	a0, sp, 0
+	addi	sp, sp, 16
+	ret
+#else
+#error Unsupported Xtensa ABI
+#endif
 
 	.section .fini
+#if defined(__XTENSA_WINDOWED_ABI__)
 	retw
+#elif defined(__XTENSA_CALL0_ABI__)
+	l32i	a0, sp, 0
+	addi	sp, sp, 16
+	ret
+#else
+#error Unsupported Xtensa ABI
+#endif
diff --git a/libc/sysdeps/linux/xtensa/mmap.S b/libc/sysdeps/linux/xtensa/mmap.S
index c05036aae..b4dd7c53b 100644
--- a/libc/sysdeps/linux/xtensa/mmap.S
+++ b/libc/sysdeps/linux/xtensa/mmap.S
@@ -48,7 +48,7 @@ ENTRY (__mmap)
 	bltz	a2, SYSCALL_ERROR_LABEL
 
 .Lpseudo_end:
-	retw
+	abi_ret
 
 PSEUDO_END (__mmap)
 
diff --git a/libc/sysdeps/linux/xtensa/setjmp.S b/libc/sysdeps/linux/xtensa/setjmp.S
index bf4691294..862bf6729 100644
--- a/libc/sysdeps/linux/xtensa/setjmp.S
+++ b/libc/sysdeps/linux/xtensa/setjmp.S
@@ -88,6 +88,7 @@ END (setjmp)
 
 ENTRY (__sigsetjmp)
 1:
+#if defined(__XTENSA_WINDOWED_ABI__)
 	/* Flush registers.  */
 	movi	a4, __window_spill
 	callx4	a4
@@ -146,6 +147,22 @@ ENTRY (__sigsetjmp)
 	callx4	a3
 	mov	a2, a6
 	retw
+#elif defined(__XTENSA_CALL0_ABI__)
+	s32i	a0, a2, 0
+	s32i	a1, a2, 4
+	s32i	a12, a2, 8
+	s32i	a13, a2, 12
+	s32i	a14, a2, 16
+	s32i	a15, a2, 20
+	mov	a12, a2
+	movi	a0, __sigjmp_save
+	callx0	a0
+	l32i	a0, a12, 0
+	l32i	a12, a12, 8
+	ret
+#else
+#error Unsupported Xtensa ABI
+#endif
 END(__sigsetjmp)
 
 weak_extern(_setjmp)
diff --git a/libc/sysdeps/linux/xtensa/syscall.S b/libc/sysdeps/linux/xtensa/syscall.S
index 0e1a5d0be..790a8d018 100644
--- a/libc/sysdeps/linux/xtensa/syscall.S
+++ b/libc/sysdeps/linux/xtensa/syscall.S
@@ -26,7 +26,7 @@
  */
 
 ENTRY (syscall)
-	l32i	a9, a1, 16	/* load extra argument from stack */
+	l32i	a9, a1, FRAMESIZE/* load extra argument from stack */
 	mov	a8, a7
 	mov	a7, a3		/* preserve a3 in a7 */
 	mov	a3, a4
@@ -37,5 +37,5 @@ ENTRY (syscall)
 	movi    a4, -4095
 	bgeu    a2, a4, SYSCALL_ERROR_LABEL
 .Lpseudo_end:
-	retw
+	abi_ret
 PSEUDO_END (syscall)
diff --git a/libc/sysdeps/linux/xtensa/sysdep.h b/libc/sysdeps/linux/xtensa/sysdep.h
index 4873a413d..ce2b0a0d6 100644
--- a/libc/sysdeps/linux/xtensa/sysdep.h
+++ b/libc/sysdeps/linux/xtensa/sysdep.h
@@ -28,13 +28,24 @@
 #define ASM_TYPE_DIRECTIVE(name, typearg) .type name, typearg
 #define ASM_SIZE_DIRECTIVE(name) .size name, . - name
 
+#if defined(__XTENSA_WINDOWED_ABI__)
+#define abi_entry(reg, frame_size) entry reg, frame_size
+#define abi_ret retw
+#elif defined(__XTENSA_CALL0_ABI__)
+#define abi_entry(reg, frame_size)
+#define abi_ret ret
+#else
+#error Unsupported Xtensa ABI
+#endif
+
+
 #define	ENTRY(name)							\
   ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME(name);				\
   ASM_TYPE_DIRECTIVE (C_SYMBOL_NAME(name), @function);			\
   .align ALIGNARG(2);							\
   LITERAL_POSITION;							\
   C_LABEL(name)								\
-  entry sp, FRAMESIZE;							\
+  abi_entry(sp, FRAMESIZE);						\
   CALL_MCOUNT
 
 #define	HIDDEN_ENTRY(name)						\
@@ -44,7 +55,7 @@
   .align ALIGNARG(2);							\
   LITERAL_POSITION;							\
   C_LABEL(name)								\
-  entry sp, FRAMESIZE;							\
+  abi_entry(sp, FRAMESIZE);						\
   CALL_MCOUNT
 
 #undef END
@@ -73,7 +84,13 @@
 #endif
 
 #ifndef FRAMESIZE
+#if defined(__XTENSA_WINDOWED_ABI__)
 #define FRAMESIZE 16
+#elif defined(__XTENSA_CALL0_ABI__)
+#define FRAMESIZE 0
+#else
+#error Unsupported Xtensa ABI
+#endif
 #endif
 #define CALL_MCOUNT		/* Do nothing.  */
 
@@ -118,7 +135,7 @@
   END (name)
 
 #undef	ret_NOERRNO
-#define ret_NOERRNO retw
+#define ret_NOERRNO abi_ret
 
 /* The function has to return the error code.  */
 #undef	PSEUDO_ERRVAL
@@ -133,7 +150,7 @@
   END (name)
 
 #undef	ret_ERRVAL
-#define ret_ERRVAL retw
+#define ret_ERRVAL abi_ret
 
 #if defined _LIBC_REENTRANT
 # if defined USE___THREAD
@@ -151,6 +168,8 @@
 	movi	a2, -1;							      \
 	j	.Lpseudo_end;
 # else /* !USE___THREAD */
+
+#if defined(__XTENSA_WINDOWED_ABI__)
 #  define SYSCALL_ERROR_HANDLER						      \
 0:	neg	a2, a2;							      \
 	mov	a6, a2;							      \
@@ -159,6 +178,24 @@
 	s32i	a2, a6, 0;						      \
 	movi	a2, -1;							      \
 	j	.Lpseudo_end;
+#elif defined(__XTENSA_CALL0_ABI__)
+#  define SYSCALL_ERROR_HANDLER						      \
+0:	neg	a2, a2;							      \
+	addi	a1, a1, -16;						      \
+	s32i	a0, a1, 0;						      \
+	s32i	a2, a1, 4;						      \
+	movi	a0, __errno_location@PLT;				      \
+	callx0	a0;						              \
+	l32i	a0, a1, 0;						      \
+	l32i	a3, a1, 4;						      \
+	addi	a1, a1, 16;						      \
+	s32i	a3, a2, 0;						      \
+	movi	a2, -1;							      \
+	j	.Lpseudo_end;
+#else
+#error Unsupported Xtensa ABI
+#endif
+
 # endif /* !USE___THREAD */
 #else /* !_LIBC_REENTRANT */
 #define SYSCALL_ERROR_HANDLER						      \
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)
diff --git a/libc/sysdeps/linux/xtensa/windowspill.S b/libc/sysdeps/linux/xtensa/windowspill.S
index 4167b2877..013025648 100644
--- a/libc/sysdeps/linux/xtensa/windowspill.S
+++ b/libc/sysdeps/linux/xtensa/windowspill.S
@@ -18,6 +18,7 @@
 
 #include <bits/xtensa-config.h>
 
+#ifdef __XTENSA_WINDOWED_ABI__
 	.text
 	.align  4
 	.literal_position
@@ -93,3 +94,5 @@ __window_spill:
 #endif
 #endif
 	retw
+
+#endif