powerpc64: Add the clone3 wrapper

It follows the internal signature:

  extern int clone3 (struct clone_args *__cl_args, size_t __size,
 int (*__func) (void *__arg), void *__arg);

The powerpc64 ABI requires an initial stackframe so the child can
store/restore the TOC.  It is create prior calling clone3 by
adjusting the stack size (since kernel will compute the stack as
stack plus size).

Checked on powerpc64-linux-gnu (power8, kernel 6.0) and
powerpc64le-linux-gnu (power9, kernel 4.18).
Reviewed-by: Paul E. Murphy <murphyp@linux.ibm.com>

sysdeps/unix/sysv/linux/powerpc/powerpc64/clone3.S

@@ -0,0 +1,157 @@
+/* The clone3 syscall wrapper.  Linux/powerpc64 version.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+#define _ERRNO_H        1
+#include <bits/errno.h>
+
+/* The userland implementation is:
+   int clone3 (struct clone_args *cl_args, size_t size,
+               int (*func)(void *arg), void *arg);
+
+   the kernel entry is:
+   int clone3 (struct clone_args *cl_args, size_t size);
+
+   The parameters are passed in registers from userland:
+   r3: cl_args
+   r4: size
+   r5: func
+   r6: arg  */
+
+#ifdef USE_PPC_SCV
+/* This is equivalent to DO_CALL_SCV, but we cannot use the macro here
+   because it uses CFI directives and we just called cfi_endproc.  */
+# define DO_CLONE3_SVC_CALL(jumpfalse)				\
+	CHECK_SCV_SUPPORT r28 jumpfalse;			\
+	mflr 	r9;						\
+	std 	r9, FRAME_LR_SAVE(r1);				\
+	.machine "push";					\
+	.machine "power9";					\
+	scv 	0;						\
+	.machine "pop";						\
+	ld 	r9, FRAME_LR_SAVE(r1);				\
+	mtlr 	r9;						\
+	/* With scv an, an error is a value -4095 <= x < 0.  */	\
+	cmpdi	cr1, r3, 0;					\
+	b	1f;
+#else
+# define DO_CLONE3_SVC_CALL(fail_branch)
+#endif
+
+        .text
+ENTRY(__clone3)
+	CALL_MCOUNT 4
+
+	/* Sanity checks args.  */
+	cmpdi	cr0, r3, 0
+	cmpdi	cr1, r5, 0
+	cror	cr0*4+eq, cr1*4+eq, cr0*4+eq
+	beq	cr0,L(badargs)
+
+	/* Save some regs in the "red zone".  */
+#ifdef USE_PPC_SCV
+	std	r28, -24(r1)
+	cfi_offset (r28, -24)
+#endif
+	std	r29, -16(r1)
+	std	r30, -8(r1)
+	cfi_offset (r29, -16)
+	cfi_offset (r30, -8)
+
+	/* Save func and arg across syscall.  */
+	mr	r30, r5		/* Function in r30.  */
+	mr	r29, r6		/* Argument in r29.  */
+
+	/* End FDE now, because in the child the unwind info will be
+	   wrong.  */
+	cfi_endproc
+
+	/* Setup a minimum stack frame for child.  It needs to first calculate
+	   the effective stack address, write the start empty backchain pointer,
+	   and update the frame size in the input cl_args.  */
+	ld	r7, 40(r3)	/* Load stack value.  */
+	ld	r8, 48(r3)	/* Load stack_size value.  */
+	li	r10, 0
+	add	r7, r7, r8	/* Calculate effective stack address.  */
+	std	r10, -FRAME_MIN_SIZE_PARM(r7)
+	addi	r8, r8, -FRAME_MIN_SIZE_PARM
+	std	r8, 48(r3)
+
+	/* Do the system call, the kernel expects:
+	   r0: system call numer
+	   r3: cl_args
+	   r4: size  */
+	li	r0, SYS_ify(clone3)
+	DO_CLONE3_SVC_CALL (0f)
+0:      DO_CALL_SC
+
+	/* With sc, error is indicated by cr0.SO.  */
+	cmpdi	cr1, r3, 0
+	crandc	cr1*4+eq, cr1*4+eq, cr0*4+so
+
+1:	bne-	cr1,L(parent)
+
+	/* Child, load the function and arguments.  */
+	std	r2, FRAME_TOC_SAVE(r1)
+	PPC64_LOAD_FUNCPTR r30
+	mr	r3, r29
+	bctrl
+	ld	r2, FRAME_TOC_SAVE(r1)
+
+	li	r0, SYS_ify(exit)
+	DO_CLONE3_SVC_CALL (2f)
+2:	DO_CALL_SC
+	/* We won't ever get here but provide a nop so that the linker
+	   will insert a toc adjusting stub if necessary.  */
+	nop
+
+L(badargs):
+	cfi_startproc
+	li	r3, EINVAL
+	TAIL_CALL_SYSCALL_ERROR
+
+L(parent):
+	/* Check if scv is available.  */
+	cmpdi cr1, r28, 0
+
+	/* Parent.  Restore registers & return.  */
+#ifdef USE_PPC_SCV
+	cfi_offset (r28, -24)
+	ld	r28, -24(r1)
+	cfi_restore (r28)
+#endif
+	cfi_offset (r29,-16)
+	cfi_offset (r30,-8)
+	ld	r29, -16(r1)
+	ld	r30, -8(r1)
+	cfi_restore (r29)
+	cfi_restore (r30)
+
+#ifdef USE_PPC_SCV
+	beq	cr1, 0f
+	RET_SCV
+	b	1f
+#endif
+0:	RET_SC
+1:	TAIL_CALL_SYSCALL_ERROR
+
+PSEUDO_END (__clone3)
+
+libc_hidden_def (__clone3)
+weak_alias (__clone3, clone3)

sysdeps/unix/sysv/linux/powerpc/sysdep.h

@@ -214,6 +214,7 @@
 #if defined(__PPC64__) || defined(__powerpc64__)
 #define HAVE_CLOCK_GETRES64_VSYSCALL	"__kernel_clock_getres"
 #define HAVE_CLOCK_GETTIME64_VSYSCALL	"__kernel_clock_gettime"
+#define HAVE_CLONE3_WRAPPER		1
 #else
 #define HAVE_CLOCK_GETRES_VSYSCALL	"__kernel_clock_getres"
 #define HAVE_CLOCK_GETTIME_VSYSCALL	"__kernel_clock_gettime"