RISC-V: ABI Implementation

This patch contains code that needs to directly know about the RISC-V
ABI, which is specified in a work-in-progress psABI document:

  https://github.com/riscv/riscv-elf-psabi-doc/blob/master/riscv-elf.md

This is meant to contain all the RISC-V code that needs to explicitly
name registers or manage in-memory structure layout.  This does not
contain any of the Linux-specific code.

2018-01-29  Palmer Dabbelt  <palmer@sifive.com>

        * sysdeps/riscv/__longjmp.S: New file.
        * sysdeps/riscv/backtrace.c: Likewise.
        * sysdeps/riscv/bits/endian.h: Likewise.
        * sysdeps/riscv/bits/setjmp.h: Likewise.
        * sysdeps/riscv/bits/wordsize.h: Likewise.
        * sysdeps/riscv/bsd-_setjmp.c: Likewise.
        * sysdeps/riscv/bsd-setjmp.c: Likewise.
        * sysdeps/riscv/dl-trampoline.S: Likewise.
        * sysdeps/riscv/gccframe.h: Likewise.
        * sysdeps/riscv/jmpbuf-offsets.h: Likewise.
        * sysdeps/riscv/jmpbuf-unwind.h: Likewise.
        * sysdeps/riscv/machine-gmon.h: Likewise.
        * sysdeps/riscv/memusage.h: Likewise.
        * sysdeps/riscv/setjmp.S: Likewise.
        * sysdeps/riscv/sys/asm.h: Likewise.
        * sysdeps/riscv/tls-macros.h: Likewise.

1 files changed, 81 insertions, 0 deletions

diff --git a/sysdeps/riscv/start.S b/sysdeps/riscv/start.S
new file mode 100644
index 0000000000..4635ddb5eb
--- /dev/null
+++ b/sysdeps/riscv/start.S
@@ -0,0 +1,81 @@
+/* Startup code compliant to the ELF RISC-V ABI.
+   Copyright (C) 1995-2018 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.
+
+   In addition to the permissions in the GNU Lesser General Public
+   License, the Free Software Foundation gives you unlimited
+   permission to link the compiled version of this file with other
+   programs, and to distribute those programs without any restriction
+   coming from the use of this file. (The GNU Lesser General Public
+   License restrictions do apply in other respects; for example, they
+   cover modification of the file, and distribution when not linked
+   into another program.)
+
+   Note that people who make modified versions of this file are not
+   obligated to grant this special exception for their modified
+   versions; it is their choice whether to do so. The GNU Lesser
+   General Public License gives permission to release a modified
+   version without this exception; this exception also makes it
+   possible to release a modified version which carries forward this
+   exception.
+
+   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
+   <http://www.gnu.org/licenses/>.  */
+
+#define __ASSEMBLY__ 1
+#include <entry.h>
+#include <sysdep.h>
+#include <sys/asm.h>
+
+/* The entry point's job is to call __libc_start_main.  Per the ABI,
+   a0 contains the address of a function to be passed to atexit.
+   __libc_start_main wants this in a5.  */
+
+ENTRY (ENTRY_POINT)
+	call  .Lload_gp
+	mv    a5, a0  /* rtld_fini.  */
+	/* main may be in a shared library.  */
+	la   a0, main
+	REG_L a1, 0(sp)      /* argc.  */
+	addi  a2, sp, SZREG  /* argv.  */
+	andi  sp, sp, ALMASK /* Align stack. */
+	lla   a3, __libc_csu_init
+	lla   a4, __libc_csu_fini
+	mv    a6, sp  /* stack_end.  */
+
+	tail  __libc_start_main@plt
+END (ENTRY_POINT)
+
+/* Dynamic links need the global pointer to be initialized prior to calling
+   any shared library's initializers, so we use preinit_array to load it.
+   This doesn't cut it for static links, though, since the global pointer
+   needs to be initialized before calling __libc_start_main in that case.
+   So we redundantly initialize it at the beginning of _start.  */
+
+.Lload_gp:
+.option push
+.option norelax
+	lla   gp, __global_pointer$
+.option pop
+	ret
+
+	.section .preinit_array,"aw"
+	.dc.a .Lload_gp
+
+/* Define a symbol for the first piece of initialized data.  */
+	.data
+	.globl __data_start
+__data_start:
+	.weak data_start
+	data_start = __data_start