Add LLVM libc sample

CMakeLists.txt

@@ -378,6 +378,12 @@ if(LLVM_TOOLCHAIN_C_LIBRARY STREQUAL llvmlibc)
         COMPONENT llvm-toolchain-llvmlibc-configs
     )
 
+    install(
+      DIRECTORY
+      ${CMAKE_CURRENT_SOURCE_DIR}/llvmlibc-samples/src
+      DESTINATION samples
+      COMPONENT llvm-toolchain-llvmlibc-configs
+    )
     # We aren't yet able to build C++ libraries to go with llvm-libc
     set(CXX_LIBS OFF)
 

docs/llvmlibc.md

@@ -60,6 +60,11 @@ For example:
 clang --config=llvmlibc.cfg --target=arm-none-eabi -march=armv7m -o hello hello.c -lsemihost -lcrt0 -Wl,--defsym=__stack=0x200000
 ```
 
+## Samples
+
+The overlay package installs a llvmlibc directory in the samples/src
+directory containing sample programs that use LLVM libc.
+
 ## Limitations of LLVM libc in LLVM Embedded Toolchain for Arm
 
 At present, this toolchain does not build any C++ libraries to go with

llvmlibc-samples/src/llvmlibc/baremetal-semihosting/Makefile

@@ -0,0 +1,37 @@
+#
+# Copyright (c) 2020-2024, Arm Limited and affiliates.
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+include ../../../Makefile.conf
+
+build: hello.elf
+
+hello.elf: *.c
+	../$(BIN_PATH)/clang --config=llvmlibc.cfg $(MICROBIT_TARGET) -nostartfiles -lsemihost -g -fno-exceptions -fno-rtti -T microbit-llvmlibc.ld -o hello.elf $^
+
+%.hex: %.elf
+	../$(BIN_PATH)/llvm-objcopy -O ihex $< $@
+
+run: hello.hex
+	qemu-system-arm -M microbit -semihosting -nographic -device loader,file=$<
+
+debug: hello.hex
+	qemu-system-arm -M microbit -semihosting -nographic -device loader,file=$< -s -S
+
+clean:
+	rm -f *.elf *.hex
+
+.PHONY: clean run debug

llvmlibc-samples/src/llvmlibc/baremetal-semihosting/crt0llvmlibc.c

@@ -0,0 +1,41 @@
+// Copyright (c) 2024, Arm Limited and affiliates.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+
+//    http://www.apache.org/licenses/LICENSE-2.0
+
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <stddef.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+
+extern int main(int argc, char** argv);
+
+extern void _platform_init();
+
+extern char __data_source[];
+extern char __data_start[];
+extern char __data_end[];
+extern char __data_size[];
+extern char __bss_start[];
+extern char __bss_end[];
+extern char __bss_size[];
+extern char __tls_base[];
+extern char __tdata_end[];
+extern char __tls_end[];
+
+void _start(void) {
+  memcpy(__data_start, __data_source, (uintptr_t) __data_size);
+  memset(__bss_start, '\0', (uintptr_t) __bss_size);
+  _platform_init();
+  _Exit(main(0, NULL));
+}

llvmlibc-samples/src/llvmlibc/baremetal-semihosting/hello.c

@@ -0,0 +1,38 @@
+// Copyright (c) 2024, Arm Limited and affiliates.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+
+//    http://www.apache.org/licenses/LICENSE-2.0
+
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <math.h>
+
+/* Example that uses heap, string and math library */
+
+int main(void) {
+  const char *hello_s = "hello ";
+  const char *world_s = "world";
+  const size_t hello_s_len = strlen(hello_s);
+  const size_t world_s_len = strlen(world_s);
+  const size_t out_s_len = hello_s_len + world_s_len + 1;
+  char *out_s = (char*) malloc(out_s_len);
+  assert(out_s_len >= hello_s_len + 1);
+  strncpy(out_s, hello_s, hello_s_len + 1);
+  assert(out_s_len >= strlen(out_s) + world_s_len + 1);
+  strncat(out_s, world_s, world_s_len + 1);
+  printf("%s %d\n", out_s, abs(-3));
+  free(out_s);
+  return 0;
+}

llvmlibc-samples/src/llvmlibc/baremetal-semihosting/microbit-llvmlibc.ld

@@ -0,0 +1,241 @@
+/*
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * Copyright © 2019 Keith Packard
+ * Copyright (c) 2024, Arm Limited and affiliates.
+ *
+ * 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. Redistributions in binary form must reproduce the above
+ *    copyright notice, this list of conditions and the following
+ *    disclaimer in the documentation and/or other materials provided
+ *    with the distribution.
+ *
+ * 3. Neither the name of the copyright holder nor the names of its
+ *    contributors may be used to endorse or promote products derived
+ *    from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND 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
+ * COPYRIGHT HOLDER OR 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.
+ */
+
+/* Linker script adapted from picolibc linker script
+ * llvm-libc uses different linker defined symbols for heap placement.
+ */
+
+/* Hard-coded for Cortex-M0 */
+MEMORY
+{
+        boot_flash (rx!w) :
+                ORIGIN = 0x00000000,
+                LENGTH = 0x3000
+        flash (rx!w) :
+                ORIGIN = 0x3000,
+                LENGTH = 0x3d000
+        ram (w!rx) :
+                ORIGIN = 0x20000000,
+                LENGTH = 0x4000
+}
+
+PHDRS
+{
+        text_boot_flash PT_LOAD;
+        text PT_LOAD;
+        ram_init PT_LOAD;
+        ram PT_LOAD;
+        tls PT_TLS;
+}
+
+SECTIONS
+{
+        PROVIDE(__stack = ORIGIN(ram) + LENGTH(ram));
+
+        .boot_flash : {
+                KEEP (*(.vectors))
+        } >boot_flash AT>boot_flash :text_boot_flash
+
+        .text : {
+
+                /* code */
+                *(.text.unlikely .text.unlikely.*)
+                *(.text.startup .text.startup.*)
+                *(.text .text.* .opd .opd.*)
+                PROVIDE (__start___lcxx_override = .);
+                *(__lcxx_override)
+                PROVIDE (__stop___lcxx_override = .);
+                *(.gnu.linkonce.t.*)
+                KEEP (*(.fini .fini.*))
+                __text_end = .;
+
+                PROVIDE (__etext = __text_end);
+                PROVIDE (_etext = __text_end);
+                PROVIDE (etext = __text_end);
+
+                /* Need to pre-align so that the symbols come after padding */
+                . = ALIGN(8);
+
+                /* lists of constructors and destructors */
+                PROVIDE_HIDDEN ( __preinit_array_start = . );
+                KEEP (*(.preinit_array))
+                PROVIDE_HIDDEN ( __preinit_array_end = . );
+
+                PROVIDE_HIDDEN ( __init_array_start = . );
+                KEEP (*(SORT_BY_INIT_PRIORITY(.init_array.*) SORT_BY_INIT_PRIORITY(.ctors.*)))
+                KEEP (*(.init_array .ctors))
+                PROVIDE_HIDDEN ( __init_array_end = . );
+
+                PROVIDE_HIDDEN ( __fini_array_start = . );
+                KEEP (*(SORT_BY_INIT_PRIORITY(.fini_array.*) SORT_BY_INIT_PRIORITY(.dtors.*)))
+                KEEP (*(.fini_array .dtors))
+                PROVIDE_HIDDEN ( __fini_array_end = . );
+
+        } >flash AT>flash :text
+
+       .rodata : {
+
+                /* read-only data */
+                *(.rdata)
+                *(.rodata .rodata.*)
+                *(.gnu.linkonce.r.*)
+
+                *(.srodata.cst16)
+                *(.srodata.cst8)
+                *(.srodata.cst4)
+                *(.srodata.cst2)
+                *(.srodata .srodata.*)
+
+        } >flash AT>flash :text
+
+        .data.rel.ro : {
+
+                /* data that needs relocating */
+                *(.data.rel.ro .data.rel.ro.*)
+
+        } >flash AT>flash :text
+
+
+        /*
+         * Needs to be in its own segment with the PLT entries first
+         * so that the linker will compute the offsets to those
+         * entries correctly.
+         */
+        .got : {
+                *(.got.plt)
+                *(.got)
+        } >flash AT>flash :text
+
+        .except_ordered : {
+                *(.gcc_except_table *.gcc_except_table.*)
+                *(.ARM.extab* .gnu.linkonce.armextab.*)
+        } >flash AT>flash :text
+
+	.except_unordered : {
+                . = ALIGN(8);
+
+                PROVIDE(__exidx_start = .);
+                *(.ARM.exidx*)
+                PROVIDE(__exidx_end = .);
+        } >flash AT>flash :text
+
+
+        .data : /* For ld.bfd:  ALIGN_WITH_INPUT */ {
+                *(.data .data.*)
+                *(.gnu.linkonce.d.*)
+
+                /* Need to pre-align so that the symbols come after padding */
+                . = ALIGN(8);
+
+                PROVIDE( __global_pointer$ = . + 0x800 );
+                PROVIDE( _gp = . + 0x8000);
+                *(.sdata .sdata.* .sdata2.*)
+                *(.gnu.linkonce.s.*)
+        } >ram AT>flash :ram_init
+        PROVIDE(__data_start = ADDR(.data));
+        PROVIDE(__data_source = LOADADDR(.data));
+
+        /* Thread local initialized data. This gets
+         * space allocated as it is expected to be placed
+         * in ram to be used as a template for TLS data blocks
+         * allocated at runtime. We're slightly abusing that
+         * by placing the data in flash where it will be copied
+         * into the allocate ram addresses by the existing
+         * data initialization code in crt0.
+         * BFD includes .tbss alignment when computing .tdata
+         * alignment, but for ld.lld we have to explicitly pad
+         * as it only guarantees usage as a TLS template works
+         * rather than supporting this use case.
+         */
+        .tdata :  ALIGN(__tls_align)  /* For ld.bfd:  ALIGN_WITH_INPUT */ {
+                *(.tdata .tdata.* .gnu.linkonce.td.*)
+                PROVIDE(__data_end = .);
+                PROVIDE(__tdata_end = .);
+        } >ram AT>flash :tls :ram_init
+        PROVIDE( __tls_base = ADDR(.tdata));
+        PROVIDE( __tdata_start = ADDR(.tdata));
+        PROVIDE( __tdata_source = LOADADDR(.tdata) );
+        PROVIDE( __tdata_source_end = LOADADDR(.tdata) + SIZEOF(.tdata) );
+        PROVIDE( __data_source_end = __tdata_source_end );
+        PROVIDE( __tdata_size = SIZEOF(.tdata) );
+
+        PROVIDE( __edata = __data_end );
+        PROVIDE( _edata = __data_end );
+        PROVIDE( edata = __data_end );
+        PROVIDE( __data_size = __data_end - __data_start );
+        PROVIDE( __data_source_size = __data_source_end - __data_source );
+
+        .tbss (NOLOAD) : {
+                *(.tbss .tbss.* .gnu.linkonce.tb.*)
+                *(.tcommon)
+                PROVIDE( __tls_end = . );
+                PROVIDE( __tbss_end = . );
+        } >ram AT>ram :tls :ram
+        PROVIDE( __bss_start = ADDR(.tbss));
+        PROVIDE( __tbss_start = ADDR(.tbss));
+        PROVIDE( __tbss_offset = ADDR(.tbss) - ADDR(.tdata) );
+        PROVIDE( __tbss_size = SIZEOF(.tbss) );
+        PROVIDE( __tls_size = __tls_end - __tls_base );
+        PROVIDE( __tls_align = MAX(ALIGNOF(.tdata), ALIGNOF(.tbss)) );
+        PROVIDE( __tls_size_align = (__tls_size + __tls_align - 1) & ~(__tls_align - 1));
+        PROVIDE( __arm32_tls_tcb_offset = MAX(8, __tls_align) );
+        PROVIDE( __arm64_tls_tcb_offset = MAX(16, __tls_align) );
+
+        .bss (NOLOAD) : {
+                *(.sbss*)
+                *(.gnu.linkonce.sb.*)
+                *(.bss .bss.*)
+                *(.gnu.linkonce.b.*)
+                *(COMMON)
+
+                /* Align the heap */
+                . = ALIGN(8);
+                __bss_end = .;
+        } >ram AT>ram :ram
+        PROVIDE( __non_tls_bss_start = ADDR(.bss) );
+        PROVIDE( __end = __bss_end );
+        _end = __bss_end;
+        PROVIDE( end = __bss_end );
+        PROVIDE( __bss_size = __bss_end - __bss_start );
+
+        /* Make the rest of memory available for heap storage
+	 * LLVM libc denotes heap with [__end, __llvm_libc_heap_limit)
+	 */
+        PROVIDE (__llvm_libc_heap_limit = __stack - (DEFINED(__stack_size) ? __stack_size : 4K));
+}
+
+ASSERT( __data_size == __data_source_size, "ERROR: .data/.tdata flash size does not match RAM size");
+