From b0f9ac365f91952f6f920c8e6aa4ddb819f47cc8 Mon Sep 17 00:00:00 2001
From: Keith Packard <keithp@keithp.com>
Date: Tue, 23 Aug 2022 22:13:08 -0700
Subject: [PATCH] picolibc: Add custom spec file fragments for using
 picolibc

The '--oslib=' option allows targets to insert an OS library after the
C library in the LIB_PATH spec file fragment. This library maps a few
POSIX APIs used by picolibc to underlying system capabilities.

The '--crt0=' option allows targets to use an alternate crt0 in place
of the usual one as provided by Picolibc.

For example, picolibc provides 'libsemihost' and 'crt0-semihost.o' on
various targets which maps some POSIX APIs to semihosting capabilities
and signals the semihosting environment when 'main' returns. These
would be used by specifying --oslib=semihost --crt0=semihost.

This patch also takes advantage of the IN_GPP conditional when
building g++ to elide exception handling contents from the executable
when not linking with the g++ driver.

Signed-off-by: Keith Packard <keithp@keithp.com>
---
 gcc/config.gcc          |    7 +++++++
 gcc/config/picolibc.h   |   44 ++++++++++++++++++++++++++++++++++++++++++++
 gcc/config/picolibc.opt |   33 +++++++++++++++++++++++++++++++++
 3 files changed, 84 insertions(+)
 create mode 100644 gcc/config/picolibc.h
 create mode 100644 gcc/config/picolibc.opt

--- a/gcc/config.gcc
+++ b/gcc/config.gcc
@@ -5931,3 +5931,10 @@
 	tm_defines="$tm_defines DEFAULT_LIBC=$default_libc"
 	;;
 esac
+
+case "$default_libc" in
+    LIBC_PICOLIBC)
+	extra_options="${extra_options} picolibc.opt"
+	tm_file="${tm_file} picolibc.h"
+	;;
+esac
--- /dev/null
+++ b/gcc/config/picolibc.h
@@ -0,0 +1,44 @@
+/* Configuration common to all targets running Picolibc.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+
+   This file is part of GCC.
+
+   GCC is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published
+   by the Free Software Foundation; either version 3, or (at your
+   option) any later version.
+
+   GCC 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 General Public
+   License for more details.
+
+   Under Section 7 of GPL version 3, you are granted additional
+   permissions described in the GCC Runtime Library Exception, version
+   3.1, as published by the Free Software Foundation.
+
+   You should have received a copy of the GNU General Public License and
+   a copy of the GCC Runtime Library Exception along with this program;
+   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifdef IN_GPP
+#define PICOLIBC_LD "picolibcpp.ld"
+#define PICOLIBC_BEGIN " crtbegin%O%s"
+#define PICOLIBC_END   "crtend%O%s"
+#else
+#define PICOLIBC_LD "picolibc.ld"
+#define PICOLIBC_BEGIN ""
+#define PICOLIBC_END   ""
+#endif
+
+#undef  LIB_SPEC
+#define LIB_SPEC "%{!T:-T" PICOLIBC_LD "} --start-group -lc %{-oslib=*:-l%*} %(libgcc) --end-group"
+
+#undef  STARTFILE_SPEC
+#define STARTFILE_SPEC "%{-crt0=*:crt0-%*%O%s; :crt0%O%s}" PICOLIBC_BEGIN
+
+#undef  ENDFILE_SPEC
+#define ENDFILE_SPEC PICOLIBC_END
+
+#define EH_TABLES_CAN_BE_READ_ONLY 1
--- /dev/null
+++ b/gcc/config/picolibc.opt
@@ -0,0 +1,33 @@
+; Processor-independent options for picolibc.
+;
+; Copyright (C) 2022 Free Software Foundation, Inc.
+;
+; This file is part of GCC.
+;
+; GCC is free software; you can redistribute it and/or modify it under
+; the terms of the GNU General Public License as published by the Free
+; Software Foundation; either version 3, or (at your option) any later
+; version.
+;
+; GCC 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 General Public License
+; for more details.
+;
+; You should have received a copy of the GNU General Public License
+; along with GCC; see the file COPYING3.  If not see
+; <http://www.gnu.org/licenses/>.
+
+-oslib
+Driver Separate Alias(-oslib=)
+
+-oslib=
+Driver Joined
+Specify an OS support library to load after libc.
+
+-crt0
+Driver Separate Alias(-crt0=)
+
+-crt0=
+Driver Joined
+Specify an alternate startup file.