Support picolibc targets

Allow --with-default-libc to control picolibc definitions

Add custom spec file fragments for use with picolibc:

 * '--oslib='. 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.

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

 * '--printf='. Allows targets to customize the version of printf linked
   from the C library.

 * '--scanf='. Allows targets to customize the version of scanf linked
   from the C library.

Signed-off-by: Keith Packard <[email protected]>

fixup

Signed-off-by: Keith Packard <[email protected]>

Author: keith-packard

gcc/config.gcc

@@ -693,7 +693,7 @@ case ${target} in
 esac
 
 # Common C libraries.
-tm_defines="$tm_defines LIBC_GLIBC=1 LIBC_UCLIBC=2 LIBC_BIONIC=3 LIBC_MUSL=4 LIBC_NEWLIB=5 LIBC_PICOLIBC=6"
+tm_defines="$tm_defines LIBC_GLIBC=1 LIBC_UCLIBC=2 LIBC_BIONIC=3 LIBC_MUSL=4 LIBC_PICOLIBC=5"
 
 default_libc=""
 
@@ -1169,14 +1169,7 @@ case ${target} in
   esac
   ;;
 *-picolibc-*)
-  # __cxa_atexit is provided.
-  default_use_cxa_atexit=yes
-  use_gcc_stdint=wrap
   default_libc=LIBC_PICOLIBC
-  case "${with_newlib}-${with_headers}" in
-  no-no) use_gcc_stdint=provide ;;
-  *) ;;
-  esac
   ;;
 
 *-*-elf|arc*-*-elf*)
@@ -6145,8 +6138,24 @@ esac
 
 case "$default_libc" in
 "")
-        ;;
+    ;;
 *)
-	tm_defines="$tm_defines DEFAULT_LIBC=$default_libc"
-	;;
+    tm_defines="$tm_defines DEFAULT_LIBC=$default_libc"
+    ;;
+esac
+
+# Targets for picolibc should include picolibc-spec.h to allow
+# use of picolibc-specific compiler flags
+case "$default_libc" in
+LIBC_PICOLIBC)
+    # __cxa_atexit is provided.
+    default_use_cxa_atexit=yes
+    use_gcc_stdint=wrap
+    tm_file="${tm_file} picolibc-spec.h"
+    extra_options="${extra_options} picolibc.opt"
+    case "${with_newlib}-${with_headers}" in
+	no-no) use_gcc_stdint=provide ;;
+	*) ;;
+    esac
+    ;;
 esac

gcc/config/picolibc-spec.h

@@ -0,0 +1,59 @@
+/* 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/>.  */
+
+#define PICOLIBC_LD "picolibc.ld"
+
+/* Default to local-exec TLS model.  */
+#undef OS_CC1_SPEC
+#define OS_CC1_SPEC " %{!ftls-model=*:-ftls-model=local-exec}"
+
+/* Pass along preprocessor definitions when --printf or --scanf are specified */
+#undef CPP_SPEC
+#define CPP_SPEC				\
+  "%{-printf=*: -D_PICOLIBC_PRINTF='%*'}"	\
+  " %{-scanf=*: -D_PICOLIBC_SCANF='%*'}"
+
+/*
+ * Add picolibc.ld if not using -r or -T and we can find it.
+ * Define vfprintf if --printf is set
+ * Define vfscanf if --scanf is set
+ */
+#undef LINK_LIBC_SPEC
+#define LINK_LIBC_SPEC							\
+  "%{!r:%{!T*: %:if-exists-then-else(%:find-file(" PICOLIBC_LD ") %T" PICOLIBC_LD ")}}"	\
+  " %{-printf=*:--defsym=" USER_LABEL_PREFIX "vfprintf=" USER_LABEL_PREFIX "__%*_vfprintf}" \
+  " %{-scanf=*:--defsym=" USER_LABEL_PREFIX "vfscanf=" USER_LABEL_PREFIX "__%*_vfscanf}"
+
+/*
+ * Place the C library, libgcc and any oslib in a link group to resolve
+ * interdependencies
+ */
+#undef  LIB_SPEC
+#define LIB_SPEC "--start-group -lc %{-oslib=*:-l%*} %(libgcc) --end-group"
+
+/* Select alternate crt0 version if --crt0 is specified */
+#undef  STARTFILE_SPEC
+#define STARTFILE_SPEC "%{-crt0=*:crt0-%*%O%s; :crt0%O%s}"
+
+#define EH_TABLES_CAN_BE_READ_ONLY 1

gcc/config/picolibc.opt

@@ -0,0 +1,47 @@
+; 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.
+
+-printf
+Driver Separate Alias(-printf=)
+
+-printf=
+Driver Joined
+Specify the printf version linked from libc.
+
+-scanf
+Driver Separate Alias(-scanf=)
+
+-scanf=
+Driver Joined
+Specify the scanf version linked from libc.

gcc/config/picolibc.opt.urls

@@ -0,0 +1,2 @@
+; Autogenerated by regenerate-opt-urls.py from gcc/config/picolibc.opt and generated HTML
+

gcc/gcc.cc

@@ -1984,7 +1984,7 @@ init_spec (void)
 #endif
 
 #if defined LINK_EH_SPEC || defined LINK_BUILDID_SPEC || \
-    defined LINKER_HASH_STYLE
+    defined LINKER_HASH_STYLE || defined LINK_LIBC_SPEC
 # ifdef LINK_BUILDID_SPEC
   /* Prepend LINK_BUILDID_SPEC to whatever link_spec we had before.  */
   obstack_grow (&obstack, LINK_BUILDID_SPEC, sizeof (LINK_BUILDID_SPEC) - 1);
@@ -2002,6 +2002,10 @@ init_spec (void)
     obstack_grow (&obstack, LINKER_HASH_STYLE, sizeof (LINKER_HASH_STYLE) - 1);
     obstack_1grow (&obstack, ' ');
   }
+# endif
+# ifdef LINK_LIBC_SPEC
+  /* Prepend LINK_LIBC_SPEC to whatever link_spec we had before. */
+  obstack_grow (&obstack, LINK_LIBC_SPEC, sizeof (LINK_LIBC_SPEC) - 1);
 # endif
   obstack_grow0 (&obstack, link_spec, strlen (link_spec));
   link_spec = XOBFINISH (&obstack, const char *);