xref: /src/libexec/ld.elf_so/arch/aarch64/rtld_start.S

/* $NetBSD: rtld_start.S,v 1.7 2024/07/23 18:11:53 riastradh Exp $ */

/*-
 * Copyright (c) 2014 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Matt Thomas of 3am Software Foundry.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*-
 * Copyright (c) 2014 The FreeBSD Foundation
 * All rights reserved.
 *
 * This software was developed by Andrew Turner under
 * sponsorship from the FreeBSD Foundation.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <machine/asm.h>

RCSID("$NetBSD: rtld_start.S,v 1.7 2024/07/23 18:11:53 riastradh Exp $")

/*
 * void _rtld_start(void (*cleanup)(void), const Obj_Entry *obj,
 *    struct ps_strings *ps_strings);
 *
 * X0		= NULL
 * X1		= NULL
 * X2		= ps_strings
 * X30 (LR)	= 0
 * X29 (FP)	= 0
 */
ENTRY_NP(_rtld_start)
	mov	x24, x2			/* save ps_strings */

	adrp	x1, :got:_DYNAMIC	/* load _DYNAMIC offset from GOT */
	ldr	x1, [x1, #:got_lo12:_DYNAMIC]

	adrp	x0, _DYNAMIC		/* get &_DYNAMIC */
	add	x0, x0, #:lo12:_DYNAMIC

	sub	x25, x0, x1		/* relocbase = &_DYNAMIC - GOT:_DYNAMIC */
	mov	x1, x25			/* pass as 2nd argument */
	bl	_C_LABEL(_rtld_relocate_nonplt_self)

	sub	sp, sp, #16		/* reserve space for returns */
	mov	x0, sp			/* pointer to reserved space */
	mov	x1, x25			/* pass relocbase */
	bl	_C_LABEL(_rtld)
	mov	x17, x0			/* save entry point */

	ldp	x0, x1, [sp], #16	/* pop cleanup & obj_main */
	mov	x2, x24			/* restore ps_strings */

	br	x17			/* call saved entry point */
END(_rtld_start)

/*
 * Upon entry from plt0 entry:
 *
 * SP+0		= &PLTGOT[n + 3]
 * SP+8		= return addr
 * X16		= &PLTGOT[2]
 */
ENTRY_NP(_rtld_bind_start)
	ldr	x9, [sp]		/* x9 = &PLTGOT[n+3] */

	/* save x0-x8 for arguments */
	stp	x0, x1, [sp, #-16]!
	stp	x2, x3, [sp, #-16]!
	stp	x4, x5, [sp, #-16]!
	stp	x6, x7, [sp, #-16]!
	stp	x8, xzr, [sp, #-16]!

	/* save q0-q7 for arguments */
	stp	q0, q1, [sp, #-32]!
	stp	q2, q3, [sp, #-32]!
	stp	q4, q5, [sp, #-32]!
	stp	q6, q7, [sp, #-32]!

	ldr	x0, [x16, #-8]	/* x0 = PLTGOT[1] */
	sub	x1, x9, x16	/* x1 = &PLTGOT[n+3] - &PLTGOT[1] = offset+8 */
	sub	x1, x1, #8	/* x1 = offset */
	lsr	x1, x1, #3	/* x1 /= sizeof(void *) */

	bl	_C_LABEL(_rtld_bind)
	mov	x17, x0		/* save result */

	/* restore q0-q7 for arguments */
	ldp	q6, q7, [sp], #32
	ldp	q4, q5, [sp], #32
	ldp	q2, q3, [sp], #32
	ldp	q0, q1, [sp], #32

	/* restore x0-x8 for arguments */
	ldp	x8, xzr, [sp], #16
	ldp	x6, x7, [sp], #16
	ldp	x4, x5, [sp], #16
	ldp	x2, x3, [sp], #16
	ldp	x0, x1, [sp], #16

	ldp	xzr, lr, [sp], #16	/* restore original lr pushed by plt0 */
	br	x17			/* call bound function */
END(_rtld_bind_start)

/*
 * Entry points used by _rtld_tlsdesc_fill.  They will be passed in x0
 * a pointer to:
 *
 *	struct rel_tlsdesc {
 *		uint64_t resolver_fnc;
 *		uint64_t resolver_arg;
 *	};
 *
 * They are called with nonstandard calling convention and must
 * preserve all registers except x0.
 */

/*
 * uint64_t@x0
 * _rtld_tlsdesc_static(struct rel_tlsdesc *rel_tlsdesc@x0);
 *
 *	Resolver function for TLS symbols resolved at load time.
 *
 *	rel_tlsdesc->resolver_arg is the offset of the static
 *	thread-local storage region, relative to the start of the TCB.
 *
 *	Nonstandard calling convention: Must preserve all registers
 *	except x0.
 */
ENTRY(_rtld_tlsdesc_static)
	.cfi_startproc
	ldr	x0, [x0, #8]		/* x0 := tcboffset */
	ret				/* return x0 = tcboffset */
	.cfi_endproc
END(_rtld_tlsdesc_static)

/*
 * uint64_t@x0
 * _rtld_tlsdesc_undef(struct rel_tlsdesc *rel_tlsdesc@x0);
 *
 *	Resolver function for weak and undefined TLS symbols.
 *
 *	rel_tlsdesc->resolver_arg is the Elf_Rela rela->r_addend.
 *
 *	Nonstandard calling convention: Must preserve all registers
 *	except x0.
 */
ENTRY(_rtld_tlsdesc_undef)
	.cfi_startproc
	str	x1, [sp, #-16]!		/* save x1 on stack */
	.cfi_adjust_cfa_offset	16

	mrs	x1, tpidr_el0		/* x1 := current thread tcb */
	ldr	x0, [x0, #8]		/* x0 := rela->r_addend */
	sub	x0, x0, x1		/* x0 := rela->r_addend - tcb */

	ldr	x1, [sp], #16		/* restore x1 from stack */
	.cfi_adjust_cfa_offset	-16
	.cfi_endproc
	ret				/* return x0 = rela->r_addend - tcb */
END(_rtld_tlsdesc_undef)

/*
 * uint64_t@x0
 * _rtld_tlsdesc_dynamic(struct rel_tlsdesc *tlsdesc@x0);
 *
 *	Resolver function for TLS symbols from dlopen().
 *
 *	rel_tlsdesc->resolver_arg is a pointer to a struct tls_data
 *	object allocated during relocation.
 *
 *	Nonstandard calling convention: Must preserve all registers
 *	except x0.
 */
ENTRY(_rtld_tlsdesc_dynamic)
	.cfi_startproc

	/* Save registers used in fast path */
	stp	x1, x2, [sp, #(-2 * 16)]!
	stp	x3, x4, [sp, #(1 * 16)]
	.cfi_adjust_cfa_offset	2 * 16
	.cfi_rel_offset		x1, 0
	.cfi_rel_offset		x2, 8
	.cfi_rel_offset		x3, 16
	.cfi_rel_offset		x4, 24

	/* Try for the fast path -- inlined version of __tls_get_addr. */

	ldr	x1, [x0, #8]		/* x1 := tlsdesc (struct tls_data *) */
	mrs	x4, tpidr_el0		/* x4 := tcb */
	ldr	x0, [x4]		/* x0 := dtv = tcb->tcb_dtv */

	ldr	x3, [x0, #-8]		/* x3 := max = DTV_MAX_INDEX(dtv) */
	ldr	x2, [x1, #0]		/* x2 := idx = tlsdesc->td_tlsindex */
	cmp	x2, x3
	b.gt	1f			/* Slow path if idx > max */

	ldr	x3, [x0, x2, lsl #3]	/* x3 := dtv[idx] */
	cbz	x3, 1f			/* Slow path if dtv[idx] is null */

	/*
	 * Fast path
	 *
	 * return (dtv[tlsdesc->td_tlsindex] + tlsdesc->td_tlsoffs - tcb)
	 */
	ldr	x2, [x1, #8]		/* x2 := offs = tlsdesc->td_tlsoffs */
	add	x2, x2, x3		/* x2 := addr = dtv[idx] + offs */
	sub	x0, x2, x4		/* x0 := addr - tcb

	/* Restore fast path registers and return */
	ldp	x3, x4, [sp, #(1 * 16)]
	ldp	x1, x2, [sp], #(2 * 16)
	.cfi_adjust_cfa_offset	-2 * 16
	ret				/* return x0 = addr - tcb */

	/*
	 * Slow path
	 *
	 * return _rtld_tls_get_addr(tp, tlsdesc->td_tlsindex,
	 *     tlsdesc->td_tlsoffs);
	 *
	 */
1:
	/* Save all integer registers */
	stp	x29, x30, [sp, #-(8 * 16)]!
	.cfi_adjust_cfa_offset	8 * 16
	.cfi_rel_offset		x29, 0
	.cfi_rel_offset		x30, 8

	stp	x5, x6, [sp, #(1 * 16)]
	stp	x7, x8, [sp, #(2 * 16)]
	stp	x9, x10, [sp, #(3 * 16)]
	stp	x11, x12, [sp, #(4 * 16)]
	stp	x13, x14, [sp, #(5 * 16)]
	stp	x15, x16, [sp, #(6 * 16)]
	stp	x17, x18, [sp, #(7 * 16)]
	.cfi_rel_offset		x5, 16
	.cfi_rel_offset		x6, 24
	.cfi_rel_offset		x7, 32
	.cfi_rel_offset		x8, 40
	.cfi_rel_offset		x9, 48
	.cfi_rel_offset		x10, 56
	.cfi_rel_offset		x11, 64
	.cfi_rel_offset		x12, 72
	.cfi_rel_offset		x13, 80
	.cfi_rel_offset		x14, 88
	.cfi_rel_offset		x15, 96
	.cfi_rel_offset		x16, 104
	.cfi_rel_offset		x17, 112
	.cfi_rel_offset		x18, 120

	/* Find the tls offset */
	mov	x0, x4			/* x0 := tcb */
	mov	x3, x1			/* x3 := tlsdesc */
	ldr	x1, [x3, #0]		/* x1 := idx = tlsdesc->td_tlsindex */
	ldr	x2, [x3, #8]		/* x2 := offs = tlsdesc->td_tlsoffs */
	bl	_rtld_tls_get_addr	/* x0 := addr = _rtld_tls_get_addr(tcb,
					 *     idx, offs) */
	mrs	x1, tpidr_el0		/* x1 := tcb */
	sub	x0, x0, x1		/* x0 := addr - tcb */

	/* Restore slow path registers */
	ldp	x17, x18, [sp, #(7 * 16)]
	ldp	x15, x16, [sp, #(6 * 16)]
	ldp	x13, x14, [sp, #(5 * 16)]
	ldp	x11, x12, [sp, #(4 * 16)]
	ldp	x9, x10, [sp, #(3 * 16)]
	ldp	x7, x8, [sp, #(2 * 16)]
	ldp	x5, x6, [sp, #(1 * 16)]
	ldp	x29, x30, [sp], #(8 * 16)
	.cfi_adjust_cfa_offset	-8 * 16
	.cfi_restore		x29
	.cfi_restore		x30

	/* Restore fast path registers and return */
	ldp	x3, x4, [sp, #16]
	ldp	x1, x2, [sp], #(2 * 16)
	.cfi_adjust_cfa_offset	-2 * 16
	.cfi_endproc
	ret				/* return x0 = addr - tcb */
END(_rtld_tlsdesc_dynamic)