[PATCH 3/3] picolibc: Add '--oslib=' option when default C library is picolibc

[Keith Packard <keithp@keithp.com>]

This 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.

For example, picolibc provides 'libsemihost' on various targets which
maps these APIs to semihosting capabilities. This would be used with
this option by specifying --oslib=semihost

This patch enables --oslib= on arm, nds32, riscv and sh.

Signed-off-by: Keith Packard <keithp@keithp.com>
---
 gcc/config.gcc            |  6 ++++++
 gcc/config/arm/elf.h      |  5 +++++
 gcc/config/nds32/elf.h    |  4 ++++
 gcc/config/picolibc.opt   | 26 ++++++++++++++++++++++++++
 gcc/config/riscv/elf.h    |  4 ++++
 gcc/config/sh/embed-elf.h |  5 +++++
 6 files changed, 50 insertions(+)
 create mode 100644 gcc/config/picolibc.opt

diff --git a/gcc/config.gcc b/gcc/config.gcc
index 0aa4bd6c3dd..80740d8f04e 100644
--- a/gcc/config.gcc
+++ b/gcc/config.gcc
@@ -5893,3 +5893,9 @@ case "$default_libc" in
 	tm_defines="$tm_defines DEFAULT_LIBC=$default_libc"
 	;;
 esac
+
+case "$default_libc" in
+    LIBC_PICOLIBC)
+	extra_options="${extra_options} picolibc.opt"
+	;;
+esac
diff --git a/gcc/config/arm/elf.h b/gcc/config/arm/elf.h
index 3d111433ede..d83ee4a1a8c 100644
--- a/gcc/config/arm/elf.h
+++ b/gcc/config/arm/elf.h
@@ -150,3 +150,8 @@
 #undef L_floatundisf
 #endif
 
+#if defined(DEFAULT_LIBC) && defined(LIBC_PICOLIBC) && DEFAULT_LIBC == LIBC_PICOLIBC
+#undef  LIB_SPEC
+#define LIB_SPEC "--start-group %(libgcc)  -lc %{-oslib=*:-l%*} --end-group"
+#endif
+
diff --git a/gcc/config/nds32/elf.h b/gcc/config/nds32/elf.h
index ebdc18cee2a..a956d531ef4 100644
--- a/gcc/config/nds32/elf.h
+++ b/gcc/config/nds32/elf.h
@@ -34,8 +34,12 @@
   " %{shared:-shared}" \
   NDS32_RELAX_SPEC
 
+#if defined(DEFAULT_LIBC) && defined(LIBC_PICOLIBC) && DEFAULT_LIBC == LIBC_PICOLIBC
+#define LIB_SPEC "--start-group %(libgcc)  -lc %{-oslib=*:-l%*} --end-group"
+#else
 #define LIB_SPEC \
   " -lc -lgloss"
+#endif
 
 #define LIBGCC_SPEC \
   " -lgcc"
diff --git a/gcc/config/picolibc.opt b/gcc/config/picolibc.opt
new file mode 100644
index 00000000000..194b3362b03
--- /dev/null
+++ b/gcc/config/picolibc.opt
@@ -0,0 +1,26 @@
+; 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.
diff --git a/gcc/config/riscv/elf.h b/gcc/config/riscv/elf.h
index f0e865d6ef4..ca906afcd52 100644
--- a/gcc/config/riscv/elf.h
+++ b/gcc/config/riscv/elf.h
@@ -27,7 +27,11 @@ along with GCC; see the file COPYING3.  If not see
 /* Link against Newlib libraries, because the ELF backend assumes Newlib.
    Handle the circular dependence between libc and libgloss. */
 #undef  LIB_SPEC
+#if defined(DEFAULT_LIBC) && defined(LIBC_PICOLIBC) && DEFAULT_LIBC == LIBC_PICOLIBC
+#define LIB_SPEC "--start-group %(libgcc)  -lc %{-oslib=*:-l%*} --end-group"
+#else
 #define LIB_SPEC "--start-group -lc %{!specs=nosys.specs:-lgloss} --end-group"
+#endif
 
 #undef  STARTFILE_SPEC
 #define STARTFILE_SPEC "crt0%O%s crtbegin%O%s"
diff --git a/gcc/config/sh/embed-elf.h b/gcc/config/sh/embed-elf.h
index 21e51dd0bb9..e8605849e07 100644
--- a/gcc/config/sh/embed-elf.h
+++ b/gcc/config/sh/embed-elf.h
@@ -34,3 +34,8 @@ along with GCC; see the file COPYING3.  If not see
   %{Os: -lgcc-Os-4-200} \
   -lgcc \
   %{!Os: -lgcc-Os-4-200}"
+
+#if defined(DEFAULT_LIBC) && defined(LIBC_PICOLIBC) && DEFAULT_LIBC == LIBC_PICOLIBC
+#undef  LIB_SPEC
+#define LIB_SPEC "--start-group %(libgcc)  -lc %{-oslib=*:-l%*} --end-group"
+#endif
-- 
2.36.1