riscv32: add ldso support, enable time64.

5 files changed, 575 insertions, 0 deletions

diff --git a/ldso/ldso/riscv32/dl-startup.h b/ldso/ldso/riscv32/dl-startup.h
new file mode 100644
index 000000000..6f16918d6
--- /dev/null
+++ b/ldso/ldso/riscv32/dl-startup.h
@@ -0,0 +1,92 @@
+/*
+ * Architecture specific code used by dl-startup.c
+ * Copyright (C) 2024 Waldemar Brodkorb <wbx@uclibc-ng.org>
+ * Ported from GNU libc
+ * Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
+ */
+
+/* Copyright (C) 2011-2019 Free Software Foundation, Inc.
+
+   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 <features.h>
+#include <sys/asm.h>
+
+#ifndef _RTLD_PROLOGUE
+# define _RTLD_PROLOGUE(entry)                                          \
+        ".globl\t" __STRING (entry) "\n\t"                              \
+        ".type\t" __STRING (entry) ", @function\n"                      \
+        __STRING (entry) ":\n\t"
+#endif
+
+#ifndef _RTLD_EPILOGUE
+# define _RTLD_EPILOGUE(entry)                                          \
+        ".size\t" __STRING (entry) ", . - " __STRING (entry) "\n\t"
+#endif
+
+#define STRINGXP(X) __STRING (X)  
+
+__asm__(\
+	".text\n\
+        " _RTLD_PROLOGUE (_start) "\
+        mv a0, sp\n\
+        jal _dl_start\n\
+        # Stash user entry point in s0.\n\
+        mv s0, a0\n\
+        # See if we were run as a command with the executable file\n\
+        # name as an extra leading argument.\n\
+        lw a0, _dl_skip_args\n\
+        # Load the original argument count.\n\
+        " STRINGXP (REG_L) " a1, 0(sp)\n\
+        # Subtract _dl_skip_args from it.\n\
+        sub a1, a1, a0\n\
+        # Adjust the stack pointer to skip _dl_skip_args words.\n\
+        sll a0, a0, " STRINGXP (PTRLOG) "\n\
+        add sp, sp, a0\n\
+        # Save back the modified argument count.\n\
+        " STRINGXP (REG_S) " a1, 0(sp)\n\
+        # Pass our finalizer function to _start.\n\
+        lla a0, _dl_fini\n\
+        # Jump to the user entry point.\n\
+        jr s0\n\
+        " _RTLD_EPILOGUE (_start) "\
+        .previous" \
+);
+
+/* Get a pointer to the argv array.  On many platforms this can be just
+ * the address of the first argument, on other platforms we need to
+ * do something a little more subtle here.  */
+#define GET_ARGV(ARGVP, ARGS) ARGVP = (((unsigned long*)ARGS)+1)
+
+/* Function calls are not safe until the GOT relocations have been done.  */
+#define NO_FUNCS_BEFORE_BOOTSTRAP
+
+/* Handle relocation of the symbols in the dynamic loader. */
+static __always_inline
+void PERFORM_BOOTSTRAP_RELOC(ELF_RELOC *rpnt, ElfW(Addr) *reloc_addr,
+	ElfW(Addr) symbol_addr, ElfW(Addr) load_addr, ElfW(Addr) *sym)
+{
+	switch (ELF_R_TYPE(rpnt->r_info)) {
+		case R_RISCV_NONE:
+			break;
+		case R_RISCV_JUMP_SLOT:
+			*reloc_addr = symbol_addr + rpnt->r_addend;
+			break;
+		default:
+			_dl_exit(1);
+	}
+}
+
+#define DL_UPDATE_LOADADDR_HDR(LOADADDR, ADDR, PHDR)
diff --git a/ldso/ldso/riscv32/dl-syscalls.h b/ldso/ldso/riscv32/dl-syscalls.h
new file mode 100644
index 000000000..f40c4fd31
--- /dev/null
+++ b/ldso/ldso/riscv32/dl-syscalls.h
@@ -0,0 +1 @@
+/* stub for arch-specific syscall issues */
diff --git a/ldso/ldso/riscv32/dl-sysdep.h b/ldso/ldso/riscv32/dl-sysdep.h
new file mode 100644
index 000000000..e0a59fddd
--- /dev/null
+++ b/ldso/ldso/riscv32/dl-sysdep.h
@@ -0,0 +1,91 @@
+/*
+ * Various assembly language/system dependent hacks that are required
+ * so that we can minimize the amount of platform specific code.
+ * Copyright (C) 2000-2004 by Erik Andersen <andersen@codepoet.org>
+ * Copyright (C) 2024 by Waldemar Brodkorb <wbx@uclibc-ng.org>
+ * Ported from GNU C Library
+ * Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
+ */
+
+/* Copyright (C) 2011-2019 Free Software Foundation, Inc.
+
+   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/>.  */
+
+/* Define this if the system uses RELOCA.  */
+#define ELF_USES_RELOCA
+
+#include <elf.h>
+#include <link.h>
+
+/* Initialization sequence for the GOT.  */
+#define INIT_GOT(GOT_BASE,MODULE) \
+{				\
+  GOT_BASE[2] = (unsigned long) _dl_linux_resolve; \
+  GOT_BASE[1] = (unsigned long) MODULE; \
+}
+
+/* Here we define the magic numbers that this dynamic loader should accept */
+#define MAGIC1 EM_RISCV
+#undef  MAGIC2
+
+/* Used for error messages */
+#define ELF_TARGET "RISC-V"
+
+struct elf_resolve;
+unsigned long _dl_linux_resolver(struct elf_resolve * tpnt, int reloc_entry);
+
+#define ELF_MACHINE_JMP_SLOT R_RISCV_JUMP_SLOT
+
+#define elf_machine_type_class(type)                            \
+  ((ELF_RTYPE_CLASS_PLT * ((type) == ELF_MACHINE_JMP_SLOT       \
+     || (__WORDSIZE == 32 && (type) == R_RISCV_TLS_DTPREL32)    \
+     || (__WORDSIZE == 32 && (type) == R_RISCV_TLS_DTPMOD32)    \
+     || (__WORDSIZE == 32 && (type) == R_RISCV_TLS_TPREL32)     \
+     || (__WORDSIZE == 64 && (type) == R_RISCV_TLS_DTPREL64)    \
+     || (__WORDSIZE == 64 && (type) == R_RISCV_TLS_DTPMOD64)    \
+     || (__WORDSIZE == 64 && (type) == R_RISCV_TLS_TPREL64)))   \
+   | (ELF_RTYPE_CLASS_COPY * ((type) == R_RISCV_COPY)))
+
+
+/* Return the link-time address of _DYNAMIC.  */
+static inline ElfW(Addr)
+elf_machine_dynamic (void)
+{
+  extern ElfW(Addr) _GLOBAL_OFFSET_TABLE_ __attribute__ ((visibility ("hidden")));
+  return _GLOBAL_OFFSET_TABLE_;
+}
+
+
+/* Return the run-time load address of the shared object.  */
+static __always_inline ElfW(Addr) __attribute__ ((unused))
+elf_machine_load_address (void)
+{
+  ElfW(Addr) load_addr;
+  __asm__ ("lla %0, _DYNAMIC" : "=r" (load_addr));
+  return load_addr - elf_machine_dynamic ();
+}
+
+static __always_inline void
+elf_machine_relative(Elf32_Addr load_off, const Elf32_Addr rel_addr,
+                     Elf32_Word relative_count)
+{
+	Elf32_Rela *rpnt = (Elf32_Rela*)rel_addr;
+	--rpnt;
+	do {
+		Elf32_Addr *const reloc_addr = (Elf32_Addr*)(load_off + (++rpnt)->r_offset);
+
+		*reloc_addr = load_off + rpnt->r_addend;
+	} while (--relative_count);
+}
diff --git a/ldso/ldso/riscv32/elfinterp.c b/ldso/ldso/riscv32/elfinterp.c
new file mode 100644
index 000000000..dc1ac994d
--- /dev/null
+++ b/ldso/ldso/riscv32/elfinterp.c
@@ -0,0 +1,295 @@
+/* RISCV ELF shared library loader suppport
+ *
+ * Copyright (C) 2001-2004 Erik Andersen
+ * Copyright (C) 2024 Waldemar Brodkorb <wbx@uclibc-ng.org>
+ *
+ * All rights reserved.
+ *
+ * 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. The name of the above contributors may not be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE 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 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.
+ */
+
+/* Program to load an ELF binary on a linux system, and run it.
+   References to symbols in sharable libraries can be resolved by either
+   an ELF sharable library or a linux style of shared library. */
+
+#include "ldso.h"
+
+extern int _dl_linux_resolve(void);
+
+unsigned long _dl_linux_resolver(struct elf_resolve *tpnt, int reloc_entry)
+{
+	ELF_RELOC *this_reloc;
+	char *strtab;
+	ElfW(Sym) *symtab;
+	int symtab_index;
+	char *rel_addr;
+	char *new_addr;
+	char **got_addr;
+	ElfW(Addr) instr_addr;
+	char *symname;
+
+	rel_addr = (char *)tpnt->dynamic_info[DT_JMPREL];
+	this_reloc = (ELF_RELOC *)(rel_addr + reloc_entry);
+	symtab_index = ELF_R_SYM(this_reloc->r_info);
+
+	symtab = (ElfW(Sym) *)tpnt->dynamic_info[DT_SYMTAB];
+	strtab = (char *)tpnt->dynamic_info[DT_STRTAB];
+	symname = strtab + symtab[symtab_index].st_name;
+
+	/* Address of jump instruction to fix up */
+	instr_addr = (this_reloc->r_offset + tpnt->loadaddr);
+	got_addr = (char **)instr_addr;
+
+	/* Get the address of the GOT entry */
+	new_addr = _dl_find_hash(symname, &_dl_loaded_modules->symbol_scope, tpnt, ELF_RTYPE_CLASS_PLT, NULL);
+	if (unlikely(!new_addr)) {
+		_dl_dprintf(2, "%s: can't resolve symbol '%s'\n", _dl_progname, symname);
+		_dl_exit(1);
+	}
+#if defined (__SUPPORT_LD_DEBUG__)
+	if (_dl_debug_bindings) {
+		_dl_dprintf(_dl_debug_file, "\nresolve function: %s", symname);
+		if (_dl_debug_detail) _dl_dprintf(_dl_debug_file,
+				"\tpatched %x ==> %x @ %x", *got_addr, new_addr, got_addr);
+	}
+	if (!_dl_debug_nofixups) {
+		*got_addr = new_addr;
+	}
+#else
+	*got_addr = new_addr;
+#endif
+	return (unsigned long)new_addr;
+}
+
+static int
+_dl_parse(struct elf_resolve *tpnt, struct r_scope_elem *scope,
+	  unsigned long rel_addr, unsigned long rel_size,
+	  int (*reloc_fnc) (struct elf_resolve *tpnt, struct r_scope_elem *scope,
+			    ELF_RELOC *rpnt, ElfW(Sym) *symtab, char *strtab))
+{
+	unsigned int i;
+	char *strtab;
+	ElfW(Sym) *symtab;
+	ELF_RELOC *rpnt;
+	int symtab_index;
+
+	/* Parse the relocation information */
+	rpnt = (ELF_RELOC *)rel_addr;
+	rel_size = rel_size / sizeof(ELF_RELOC);
+
+	symtab = (ElfW(Sym) *)tpnt->dynamic_info[DT_SYMTAB];
+	strtab = (char *)tpnt->dynamic_info[DT_STRTAB];
+
+	for (i = 0; i < rel_size; i++, rpnt++) {
+		int res;
+
+		symtab_index = ELF_R_SYM(rpnt->r_info);
+
+		debug_sym(symtab, strtab, symtab_index);
+		debug_reloc(symtab, strtab, rpnt);
+
+		res = reloc_fnc(tpnt, scope, rpnt, symtab, strtab);
+
+		if (res==0) 
+			continue;
+
+		_dl_dprintf(2, "\n%s: ", _dl_progname);
+
+		if (symtab_index)
+			_dl_dprintf(2, "symbol '%s': ", 
+				strtab + symtab[symtab_index].st_name);
+
+		if (unlikely(res < 0)) {
+		        int reloc_type = ELF_R_TYPE(rpnt->r_info);
+			_dl_dprintf(2, "can't handle reloc type %x\n", reloc_type);
+			_dl_exit(-res);
+		} else if (unlikely(res > 0)) {
+			_dl_dprintf(2, "can't resolve symbol\n");
+			return res;
+		}
+	  }
+
+	  return 0;
+}
+
+static int
+_dl_do_reloc (struct elf_resolve *tpnt, struct r_scope_elem *scope,
+	      ELF_RELOC *rpnt, ElfW(Sym) *symtab, char *strtab)
+{
+	int reloc_type;
+	int symtab_index;
+	char *symname;
+#if defined USE_TLS && USE_TLS
+	struct elf_resolve *tls_tpnt = NULL;
+#endif
+	struct symbol_ref sym_ref;
+	ElfW(Addr) *reloc_addr;
+	ElfW(Addr) symbol_addr;
+#if defined (__SUPPORT_LD_DEBUG__)
+	ElfW(Addr) old_val;
+#endif
+
+	reloc_addr = (ElfW(Addr)*)(tpnt->loadaddr + (unsigned long)rpnt->r_offset);
+	reloc_type = ELF_R_TYPE(rpnt->r_info);
+	symtab_index = ELF_R_SYM(rpnt->r_info);
+	sym_ref.sym = &symtab[symtab_index];
+	sym_ref.tpnt = NULL;
+	symbol_addr = 0;
+	symname = strtab + sym_ref.sym->st_name;
+
+	if (symtab_index) {
+		symbol_addr = (ElfW(Addr))_dl_find_hash(symname, scope, tpnt,
+				elf_machine_type_class(reloc_type), &sym_ref);
+
+		/*
+		 * We want to allow undefined references to weak symbols - this might
+		 * have been intentional.  We should not be linking local symbols
+		 * here, so all bases should be covered.
+		 */
+		if (unlikely (!symbol_addr && 
+			(ELF_ST_TYPE(symtab[symtab_index].st_info) != STT_TLS) &&
+			(ELF_ST_BIND(symtab[symtab_index].st_info) != STB_WEAK))) {
+			return 1;
+		}
+		if (_dl_trace_prelink) {
+			_dl_debug_lookup (symname, tpnt, &symtab[symtab_index],
+						&sym_ref, elf_machine_type_class(reloc_type));
+		}
+#if defined USE_TLS && USE_TLS
+		tls_tpnt = sym_ref.tpnt;
+#endif
+	} else {
+		/*
+		 * Relocs against STN_UNDEF are usually treated as using a
+		 * symbol value of zero, and using the module containing the
+		 * reloc itself.
+		 */
+		symbol_addr = sym_ref.sym->st_value;
+#if defined USE_TLS && USE_TLS
+		tls_tpnt = tpnt;
+#endif
+	}
+
+#if defined (__SUPPORT_LD_DEBUG__)
+	old_val = *reloc_addr;
+#endif
+
+	switch (reloc_type) {
+		case R_RISCV_NONE:
+			break;
+		case R_RISCV_32: 		/* REL_SYMBOLIC */
+		case R_RISCV_JUMP_SLOT:	/* REL_PLT */
+			*reloc_addr = symbol_addr + rpnt->r_addend;
+			break;
+		case R_RISCV_RELATIVE:
+			*reloc_addr += tpnt->loadaddr + rpnt->r_addend;
+			break;
+		case R_RISCV_COPY:
+			if (symbol_addr) {
+				_dl_memcpy((char *)reloc_addr, (char *)symbol_addr,
+							sym_ref.sym->st_size);
+			}
+			break;
+#if defined USE_TLS && USE_TLS
+		case R_RISCV_TLS_DTPMOD32:
+			*reloc_addr = tls_tpnt->l_tls_modid;
+			break;
+		case R_RISCV_TLS_DTPREL32:
+			*reloc_addr = symbol_addr + rpnt->r_addend;
+			break;
+		case R_RISCV_TLS_TPREL32:
+			CHECK_STATIC_TLS ((struct link_map *) tls_tpnt);
+			*reloc_addr = tls_tpnt->l_tls_offset + symbol_addr + rpnt->r_addend - TLS_TCB_SIZE;
+			break;
+#endif
+		default:
+			return -1; /*call _dl_exit(1) */
+	}
+
+#if defined (__SUPPORT_LD_DEBUG__)
+	if (_dl_debug_reloc && _dl_debug_detail) {
+		_dl_dprintf(_dl_debug_file, "\tpatched: %x ==> %x @ %x\n", 
+				old_val, *reloc_addr, reloc_addr);
+	}
+#endif
+
+	return 0;
+}
+
+#undef __RISCV_LAZY_RELOC_WORKS
+#ifdef __RISCV_LAZY_RELOC_WORKS
+static int
+_dl_do_lazy_reloc (struct elf_resolve *tpnt, struct r_scope_elem *scope,
+		   ELF_RELOC *rpnt, ElfW(Sym) *symtab, char *strtab)
+{
+	int reloc_type;
+	ElfW(Addr) *reloc_addr;
+#if defined (__SUPPORT_LD_DEBUG__)
+	ElfW(Addr) old_val;
+#endif
+
+	(void)scope;
+	(void)strtab;
+
+	reloc_addr = (ElfW(Addr)*)(tpnt->loadaddr + rpnt->r_offset);
+	reloc_type = ELF_R_TYPE(rpnt->r_info);
+
+#if defined (__SUPPORT_LD_DEBUG__)
+	old_val = *reloc_addr;
+#endif
+
+	switch (reloc_type) {
+		case R_RISCV_NONE:
+			break;
+		case R_RISCV_JUMP_SLOT:
+			break;
+		default:
+			return -1; /*call _dl_exit(1) */
+	}
+
+#if defined (__SUPPORT_LD_DEBUG__)
+	if (_dl_debug_reloc && _dl_debug_detail) {
+		_dl_dprintf(_dl_debug_file, "\tpatched_lazy: %x ==> %x @ %x\n",
+			    old_val, *reloc_addr, reloc_addr);
+	}
+#endif
+
+	return 0;
+}
+#endif
+
+void _dl_parse_lazy_relocation_information(struct dyn_elf *rpnt,
+	unsigned long rel_addr, unsigned long rel_size)
+{
+#ifdef __RISCV_LAZY_RELOC_WORKS
+	(void)_dl_parse(rpnt->dyn, NULL, rel_addr, rel_size, _dl_do_lazy_reloc);
+#else
+	_dl_parse_relocation_information(rpnt, &_dl_loaded_modules->symbol_scope,
+									rel_addr, rel_size);
+#endif
+}
+
+int _dl_parse_relocation_information(struct dyn_elf *rpnt,
+	struct r_scope_elem *scope, unsigned long rel_addr, unsigned long rel_size)
+{
+	return _dl_parse(rpnt->dyn, scope, rel_addr, rel_size, _dl_do_reloc);
+}
diff --git a/ldso/ldso/riscv32/resolve.S b/ldso/ldso/riscv32/resolve.S
new file mode 100644
index 000000000..bfa91ecdb
--- /dev/null
+++ b/ldso/ldso/riscv32/resolve.S
@@ -0,0 +1,96 @@
+/*
+ * Copyright (C) 2024 by Waldemar Brodkorb <wbx@uclibc-ng.org>
+ * Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
+ * ported from GNU libc
+ */
+
+/* Copyright (C) 2017-2019 Free Software Foundation, Inc.
+
+   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 <features.h>
+
+#include <sysdep.h>
+#include <sys/asm.h>
+
+/* Assembler veneer called from the PLT header code for lazy loading.
+   The PLT header passes its own args in t0-t2.  */
+
+#ifdef __riscv_float_abi_soft
+# define FRAME_SIZE (-((-10 * SZREG) & ALMASK))
+#else
+# define FRAME_SIZE (-((-10 * SZREG - 8 * SZFREG) & ALMASK))
+#endif
+
+ENTRY (_dl_linux_resolve)
+  # Save arguments to stack.
+  addi sp, sp, -FRAME_SIZE
+  REG_S ra, 9*SZREG(sp)
+  REG_S a0, 1*SZREG(sp)
+  REG_S a1, 2*SZREG(sp)
+  REG_S a2, 3*SZREG(sp)
+  REG_S a3, 4*SZREG(sp)
+  REG_S a4, 5*SZREG(sp)
+  REG_S a5, 6*SZREG(sp)
+  REG_S a6, 7*SZREG(sp)
+  REG_S a7, 8*SZREG(sp)
+
+#ifndef __riscv_float_abi_soft
+  FREG_S fa0, (10*SZREG + 0*SZFREG)(sp)
+  FREG_S fa1, (10*SZREG + 1*SZFREG)(sp)
+  FREG_S fa2, (10*SZREG + 2*SZFREG)(sp)
+  FREG_S fa3, (10*SZREG + 3*SZFREG)(sp)
+  FREG_S fa4, (10*SZREG + 4*SZFREG)(sp)
+  FREG_S fa5, (10*SZREG + 5*SZFREG)(sp)
+  FREG_S fa6, (10*SZREG + 6*SZFREG)(sp)
+  FREG_S fa7, (10*SZREG + 7*SZFREG)(sp)
+#endif
+
+  # Update .got.plt and obtain runtime address of callee.
+  slli a1, t1, 1
+  mv a0, t0       # link map
+  add a1, a1, t1  # reloc offset (== thrice the .got.plt offset)
+  la a2, _dl_fixup
+  jalr a2
+  mv t1, a0
+
+  # Restore arguments from stack.
+  REG_L ra, 9*SZREG(sp)
+  REG_L a0, 1*SZREG(sp)
+  REG_L a1, 2*SZREG(sp)
+  REG_L a2, 3*SZREG(sp)
+  REG_L a3, 4*SZREG(sp)
+  REG_L a4, 5*SZREG(sp)
+  REG_L a5, 6*SZREG(sp)
+  REG_L a6, 7*SZREG(sp)
+  REG_L a7, 8*SZREG(sp)
+
+#ifndef __riscv_float_abi_soft
+  FREG_L fa0, (10*SZREG + 0*SZFREG)(sp)
+  FREG_L fa1, (10*SZREG + 1*SZFREG)(sp)
+  FREG_L fa2, (10*SZREG + 2*SZFREG)(sp)
+  FREG_L fa3, (10*SZREG + 3*SZFREG)(sp)
+  FREG_L fa4, (10*SZREG + 4*SZFREG)(sp)
+  FREG_L fa5, (10*SZREG + 5*SZFREG)(sp)
+  FREG_L fa6, (10*SZREG + 6*SZFREG)(sp)
+  FREG_L fa7, (10*SZREG + 7*SZFREG)(sp)
+#endif
+
+  addi sp, sp, FRAME_SIZE
+
+  # Invoke the callee.
+  jr t1
+END (_dl_linux_resolve)
+