[libc-commits] [libc] [libc] Basic implementation of crt0 (PR #146863)
William Huynh via libc-commits
libc-commits at lists.llvm.org
Thu Jul 31 03:09:19 PDT 2025
https://github.com/saturn691 updated https://github.com/llvm/llvm-project/pull/146863
>From ad377724798116f5c3b219436555afa64f113393 Mon Sep 17 00:00:00 2001
From: William Huynh <William.Huynh at arm.com>
Date: Thu, 3 Jul 2025 12:35:30 +0100
Subject: [PATCH 1/5] [libc] Draft implementation of crt0
---
libc/startup/baremetal/CMakeLists.txt | 60 ++++++++++++++
libc/startup/baremetal/arm/CMakeLists.txt | 16 ++++
libc/startup/baremetal/arm/start.cpp | 95 +++++++++++++++++++++++
libc/startup/baremetal/fini.cpp | 9 +--
libc/startup/baremetal/fini.h | 16 ++++
libc/startup/baremetal/init.cpp | 9 +--
libc/startup/baremetal/init.h | 18 +++++
7 files changed, 211 insertions(+), 12 deletions(-)
create mode 100644 libc/startup/baremetal/arm/CMakeLists.txt
create mode 100644 libc/startup/baremetal/arm/start.cpp
create mode 100644 libc/startup/baremetal/fini.h
create mode 100644 libc/startup/baremetal/init.h
diff --git a/libc/startup/baremetal/CMakeLists.txt b/libc/startup/baremetal/CMakeLists.txt
index 276fe33876825..4deead2b9e21d 100644
--- a/libc/startup/baremetal/CMakeLists.txt
+++ b/libc/startup/baremetal/CMakeLists.txt
@@ -1,3 +1,33 @@
+function(add_startup_object name)
+ cmake_parse_arguments(
+ "ADD_STARTUP_OBJECT"
+ "ALIAS" # Option argument
+ "SRC" # Single value arguments
+ "DEPENDS;COMPILE_OPTIONS" # Multi value arguments
+ ${ARGN}
+ )
+
+ get_fq_target_name(${name} fq_target_name)
+ if(ADD_STARTUP_OBJECT_ALIAS)
+ get_fq_deps_list(fq_dep_list ${ADD_STARTUP_OBJECT_DEPENDS})
+ add_library(${fq_target_name} ALIAS ${fq_dep_list})
+ return()
+ endif()
+
+ add_object_library(
+ ${name}
+ SRCS ${ADD_STARTUP_OBJECT_SRC}
+ COMPILE_OPTIONS ${ADD_STARTUP_OBJECT_COMPILE_OPTIONS}
+ ${ADD_STARTUP_OBJECT_UNPARSED_ARGUMENTS}
+ DEPENDS ${ADD_STARTUP_OBJECT_DEPENDS}
+ )
+ set_target_properties(
+ ${fq_target_name}
+ PROPERTIES
+ OUTPUT_NAME ${name}.o
+ )
+endfunction()
+
add_entrypoint_object(
init
SRCS
@@ -5,6 +35,8 @@ add_entrypoint_object(
DEPENDS
libc.hdr.stdint_proxy
libc.src.__support.common
+ HDRS
+ init.h
)
add_entrypoint_object(
@@ -14,4 +46,32 @@ add_entrypoint_object(
DEPENDS
libc.hdr.stdint_proxy
libc.src.__support.common
+ HDRS
+ fini.h
)
+
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_ARCHITECTURE})
+ add_subdirectory(${LIBC_TARGET_ARCHITECTURE})
+else()
+ message(WARNING "Cannot build 'crt1.o' for ${LIBC_TARGET_ARCHITECTURE} yet.")
+ return()
+endif()
+
+add_startup_object(
+ crt1
+ ALIAS
+ DEPENDS
+ .${LIBC_TARGET_ARCHITECTURE}.crt1
+)
+
+add_custom_target(libc-startup)
+set(startup_components crt1)
+foreach(target IN LISTS startup_components)
+ set(fq_target_name libc.startup.baremetal.${target})
+ add_dependencies(libc-startup ${fq_target_name})
+ install(FILES $<TARGET_OBJECTS:${fq_target_name}>
+ DESTINATION ${LIBC_INSTALL_LIBRARY_DIR}
+ RENAME $<TARGET_PROPERTY:${fq_target_name},OUTPUT_NAME>
+ COMPONENT libc)
+endforeach()
+
diff --git a/libc/startup/baremetal/arm/CMakeLists.txt b/libc/startup/baremetal/arm/CMakeLists.txt
new file mode 100644
index 0000000000000..3f6c4041341f4
--- /dev/null
+++ b/libc/startup/baremetal/arm/CMakeLists.txt
@@ -0,0 +1,16 @@
+add_startup_object(
+ crt1
+ SRC
+ start.cpp
+ DEPENDS
+ libc.src.stdlib.atexit
+ libc.src.stdlib.exit
+ libc.src.string.memcpy
+ libc.src.string.memset
+ libc.startup.baremetal.init
+ libc.startup.baremetal.fini
+ COMPILE_OPTIONS
+ -ffreestanding # To avoid compiler warnings about calling the main function.
+ -fno-builtin
+)
+get_fq_target_name(crt1 fq_name)
diff --git a/libc/startup/baremetal/arm/start.cpp b/libc/startup/baremetal/arm/start.cpp
new file mode 100644
index 0000000000000..b40e7116c4001
--- /dev/null
+++ b/libc/startup/baremetal/arm/start.cpp
@@ -0,0 +1,95 @@
+//===-- Implementation of crt for arm -------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/macros/config.h"
+#include "src/stdlib/atexit.h"
+#include "src/stdlib/exit.h"
+#include "src/string/memcpy.h"
+#include "src/string/memset.h"
+#include "startup/baremetal/fini.h"
+#include "startup/baremetal/init.h"
+
+#include <stdint.h>
+
+extern "C" {
+int main(int argc, char **argv);
+void _start();
+
+// Semihosting library initialisation if applicable. Required for printf, etc.
+[[gnu::weak]] void _platform_init() {}
+
+// These symbols are provided by the linker. The exact names are not defined by
+// a standard.
+extern uintptr_t __stack;
+extern uintptr_t __data_source[];
+extern uintptr_t __data_start[];
+extern uintptr_t __data_size[];
+extern uintptr_t __bss_start[];
+extern uintptr_t __bss_size[];
+
+// Based on
+// https://developer.arm.com/documentation/107565/0101/Use-case-examples/Generic-Information/What-is-inside-a-program-image-/Vector-table
+void NMI_Handler() {}
+void HardFault_Handler() { LIBC_NAMESPACE::exit(1); }
+void MemManage_Handler() { LIBC_NAMESPACE::exit(1); }
+void BusFault_Handler() { LIBC_NAMESPACE::exit(1); }
+void UsageFault_Handler() { LIBC_NAMESPACE::exit(1); }
+void SVC_Handler() {}
+void DebugMon_Handler() {}
+void PendSV_Handler() {}
+void SysTick_Handler() {}
+
+// Architecturally the bottom 7 bits of VTOR are zero, meaning the vector table
+// has to be 128-byte aligned, however an implementation can require more bits
+// to be zero and Cortex-M23 can require up to 10, so 1024-byte align the vector
+// table.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wglobal-constructors"
+using HandlerType = void (*)(void);
+const HandlerType vector_table[]
+ __attribute__((section(".vectors"), aligned(1024), used)) = {
+ (HandlerType)&__stack, // SP
+ _start, // Reset
+ NMI_Handler, // NMI Handler
+ HardFault_Handler, // Hard Fault Handlerß
+ MemManage_Handler, // MPU Fault Han`dler
+ BusFault_Handler, // Bus Fault Handler
+ UsageFault_Handler, // Usage Fault Handler
+ 0, // Reserved
+ 0, // Reserved
+ 0, // Reserved
+ 0, // Reserved
+ SVC_Handler, // SVC Handler
+ DebugMon_Handler, // Debug Monitor Handler
+ 0, // Reserved
+ PendSV_Handler, // PendSV Handler
+ SysTick_Handler, // SysTick Handler
+ // Unused
+};
+} // extern "C"
+#pragma clang diagnostic pop
+
+namespace LIBC_NAMESPACE_DECL {
+[[noreturn]] void do_start() {
+ // FIXME: set up the QEMU test environment
+
+ // Perform the equivalent of scatterloading
+ memcpy(__data_start, __data_source, (uintptr_t)__data_size);
+ memset(__bss_start, '\0', (uintptr_t)__bss_size);
+ __libc_init_array();
+
+ _platform_init();
+ LIBC_NAMESPACE::atexit(&__libc_fini_array);
+ LIBC_NAMESPACE::exit(main(0, 0));
+}
+} // namespace LIBC_NAMESPACE_DECL
+
+extern "C" void _start() {
+ asm volatile("mov sp, %0" : : "r"(&__stack));
+ asm volatile("bl %0" : : "X"(LIBC_NAMESPACE::do_start));
+}
diff --git a/libc/startup/baremetal/fini.cpp b/libc/startup/baremetal/fini.cpp
index 64af842572ecd..159dae8f1128d 100644
--- a/libc/startup/baremetal/fini.cpp
+++ b/libc/startup/baremetal/fini.cpp
@@ -6,17 +6,16 @@
//
//===----------------------------------------------------------------------===//
+#include "startup/baremetal/fini.h"
+
+#include "startup/baremetal/fini.h"
+
#include "hdr/stdint_proxy.h"
#include "src/__support/macros/config.h"
#include <stddef.h>
namespace LIBC_NAMESPACE_DECL {
-extern "C" {
-extern uintptr_t __fini_array_start[];
-extern uintptr_t __fini_array_end[];
-}
-
using FiniCallback = void(void);
extern "C" void __libc_fini_array(void) {
diff --git a/libc/startup/baremetal/fini.h b/libc/startup/baremetal/fini.h
new file mode 100644
index 0000000000000..c3d53601d92cc
--- /dev/null
+++ b/libc/startup/baremetal/fini.h
@@ -0,0 +1,16 @@
+//===-- Implementation header of __libc_fini_array ------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <stdint.h>
+
+extern "C" {
+extern uintptr_t __fini_array_start[];
+extern uintptr_t __fini_array_end[];
+
+void __libc_fini_array(void);
+} // extern "C"
diff --git a/libc/startup/baremetal/init.cpp b/libc/startup/baremetal/init.cpp
index 995609c1bf412..4d67fa84e557f 100644
--- a/libc/startup/baremetal/init.cpp
+++ b/libc/startup/baremetal/init.cpp
@@ -7,18 +7,13 @@
//===----------------------------------------------------------------------===//
#include "hdr/stdint_proxy.h"
+#include "startup/baremetal/init.h"
+
#include "src/__support/macros/config.h"
#include <stddef.h>
namespace LIBC_NAMESPACE_DECL {
-extern "C" {
-extern uintptr_t __preinit_array_start[];
-extern uintptr_t __preinit_array_end[];
-extern uintptr_t __init_array_start[];
-extern uintptr_t __init_array_end[];
-}
-
using InitCallback = void(void);
extern "C" void __libc_init_array(void) {
diff --git a/libc/startup/baremetal/init.h b/libc/startup/baremetal/init.h
new file mode 100644
index 0000000000000..2b294e33c98e6
--- /dev/null
+++ b/libc/startup/baremetal/init.h
@@ -0,0 +1,18 @@
+//===-- Implementation header of __libc_init_array ------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <stdint.h>
+
+extern "C" {
+extern uintptr_t __preinit_array_start[];
+extern uintptr_t __preinit_array_end[];
+extern uintptr_t __init_array_start[];
+extern uintptr_t __init_array_end[];
+
+void __libc_init_array(void);
+} // extern "C"
>From b8c1bbf959fe139e803fded085ab94d936eeb7d9 Mon Sep 17 00:00:00 2001
From: William Huynh <William.Huynh at arm.com>
Date: Tue, 22 Jul 2025 13:10:33 +0100
Subject: [PATCH 2/5] Apply suggestions from @vhscampos
---
libc/startup/baremetal/CMakeLists.txt | 1 -
libc/startup/baremetal/arm/CMakeLists.txt | 1 +
libc/startup/baremetal/arm/start.cpp | 3 ---
3 files changed, 1 insertion(+), 4 deletions(-)
diff --git a/libc/startup/baremetal/CMakeLists.txt b/libc/startup/baremetal/CMakeLists.txt
index 4deead2b9e21d..12db526eed70a 100644
--- a/libc/startup/baremetal/CMakeLists.txt
+++ b/libc/startup/baremetal/CMakeLists.txt
@@ -74,4 +74,3 @@ foreach(target IN LISTS startup_components)
RENAME $<TARGET_PROPERTY:${fq_target_name},OUTPUT_NAME>
COMPONENT libc)
endforeach()
-
diff --git a/libc/startup/baremetal/arm/CMakeLists.txt b/libc/startup/baremetal/arm/CMakeLists.txt
index 3f6c4041341f4..b1539f3bfb4f2 100644
--- a/libc/startup/baremetal/arm/CMakeLists.txt
+++ b/libc/startup/baremetal/arm/CMakeLists.txt
@@ -12,5 +12,6 @@ add_startup_object(
COMPILE_OPTIONS
-ffreestanding # To avoid compiler warnings about calling the main function.
-fno-builtin
+ -Wno-global-constructors # To allow vector table initialization
)
get_fq_target_name(crt1 fq_name)
diff --git a/libc/startup/baremetal/arm/start.cpp b/libc/startup/baremetal/arm/start.cpp
index b40e7116c4001..67af586434e2a 100644
--- a/libc/startup/baremetal/arm/start.cpp
+++ b/libc/startup/baremetal/arm/start.cpp
@@ -48,8 +48,6 @@ void SysTick_Handler() {}
// has to be 128-byte aligned, however an implementation can require more bits
// to be zero and Cortex-M23 can require up to 10, so 1024-byte align the vector
// table.
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wglobal-constructors"
using HandlerType = void (*)(void);
const HandlerType vector_table[]
__attribute__((section(".vectors"), aligned(1024), used)) = {
@@ -72,7 +70,6 @@ const HandlerType vector_table[]
// Unused
};
} // extern "C"
-#pragma clang diagnostic pop
namespace LIBC_NAMESPACE_DECL {
[[noreturn]] void do_start() {
>From 51704576cada227fb0e2ee7c84729b3023029aeb Mon Sep 17 00:00:00 2001
From: William Huynh <williamhuynh2002 at gmail.com>
Date: Wed, 23 Jul 2025 09:42:27 +0100
Subject: [PATCH 3/5] Update libc/startup/baremetal/arm/start.cpp
Co-authored-by: Michael Jones <michaelrj at google.com>
---
libc/startup/baremetal/arm/start.cpp | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/libc/startup/baremetal/arm/start.cpp b/libc/startup/baremetal/arm/start.cpp
index 67af586434e2a..123efc4750941 100644
--- a/libc/startup/baremetal/arm/start.cpp
+++ b/libc/startup/baremetal/arm/start.cpp
@@ -76,8 +76,8 @@ namespace LIBC_NAMESPACE_DECL {
// FIXME: set up the QEMU test environment
// Perform the equivalent of scatterloading
- memcpy(__data_start, __data_source, (uintptr_t)__data_size);
- memset(__bss_start, '\0', (uintptr_t)__bss_size);
+ LIBC_NAMESPACE::memcpy(__data_start, __data_source, (uintptr_t)__data_size);
+ LIBC_NAMESPACE::memset(__bss_start, '\0', (uintptr_t)__bss_size);
__libc_init_array();
_platform_init();
>From 9cfb320a67664cb8ede8050fb6b8ee3a8e736263 Mon Sep 17 00:00:00 2001
From: William Huynh <William.Huynh at arm.com>
Date: Wed, 23 Jul 2025 11:24:32 +0100
Subject: [PATCH 4/5] Apply suggestions from @vhscampos 2
---
libc/startup/baremetal/CMakeLists.txt | 16 +++++++---------
libc/startup/baremetal/arm/CMakeLists.txt | 1 -
2 files changed, 7 insertions(+), 10 deletions(-)
diff --git a/libc/startup/baremetal/CMakeLists.txt b/libc/startup/baremetal/CMakeLists.txt
index 12db526eed70a..b70a065743418 100644
--- a/libc/startup/baremetal/CMakeLists.txt
+++ b/libc/startup/baremetal/CMakeLists.txt
@@ -65,12 +65,10 @@ add_startup_object(
)
add_custom_target(libc-startup)
-set(startup_components crt1)
-foreach(target IN LISTS startup_components)
- set(fq_target_name libc.startup.baremetal.${target})
- add_dependencies(libc-startup ${fq_target_name})
- install(FILES $<TARGET_OBJECTS:${fq_target_name}>
- DESTINATION ${LIBC_INSTALL_LIBRARY_DIR}
- RENAME $<TARGET_PROPERTY:${fq_target_name},OUTPUT_NAME>
- COMPONENT libc)
-endforeach()
+
+set(fq_target_name libc.startup.baremetal.${LIBC_TARGET_ARCHITECTURE}.crt1)
+add_dependencies(libc-startup ${fq_target_name})
+install(FILES $<TARGET_OBJECTS:${fq_target_name}>
+ DESTINATION ${LIBC_INSTALL_LIBRARY_DIR}
+ RENAME $<TARGET_PROPERTY:${fq_target_name},OUTPUT_NAME>
+ COMPONENT libc)
diff --git a/libc/startup/baremetal/arm/CMakeLists.txt b/libc/startup/baremetal/arm/CMakeLists.txt
index b1539f3bfb4f2..f75bd893c68bc 100644
--- a/libc/startup/baremetal/arm/CMakeLists.txt
+++ b/libc/startup/baremetal/arm/CMakeLists.txt
@@ -14,4 +14,3 @@ add_startup_object(
-fno-builtin
-Wno-global-constructors # To allow vector table initialization
)
-get_fq_target_name(crt1 fq_name)
>From f2138be237e8b1c9054cd667d99e40e75b84d849 Mon Sep 17 00:00:00 2001
From: William Huynh <William.Huynh at arm.com>
Date: Thu, 31 Jul 2025 11:08:04 +0100
Subject: [PATCH 5/5] Add suggestion from @petrhosek and rebase
---
libc/startup/baremetal/CMakeLists.txt | 1 +
libc/startup/baremetal/fini.cpp | 3 ---
libc/startup/baremetal/fini.h | 2 +-
libc/startup/baremetal/init.cpp | 1 -
libc/startup/baremetal/init.h | 2 +-
5 files changed, 3 insertions(+), 6 deletions(-)
diff --git a/libc/startup/baremetal/CMakeLists.txt b/libc/startup/baremetal/CMakeLists.txt
index b70a065743418..e361000f788ea 100644
--- a/libc/startup/baremetal/CMakeLists.txt
+++ b/libc/startup/baremetal/CMakeLists.txt
@@ -1,3 +1,4 @@
+# TODO: Use generic "add_startup_object" https://github.com/llvm/llvm-project/issues/133156
function(add_startup_object name)
cmake_parse_arguments(
"ADD_STARTUP_OBJECT"
diff --git a/libc/startup/baremetal/fini.cpp b/libc/startup/baremetal/fini.cpp
index 159dae8f1128d..66714e2f8f92d 100644
--- a/libc/startup/baremetal/fini.cpp
+++ b/libc/startup/baremetal/fini.cpp
@@ -8,9 +8,6 @@
#include "startup/baremetal/fini.h"
-#include "startup/baremetal/fini.h"
-
-#include "hdr/stdint_proxy.h"
#include "src/__support/macros/config.h"
#include <stddef.h>
diff --git a/libc/startup/baremetal/fini.h b/libc/startup/baremetal/fini.h
index c3d53601d92cc..74e9601983a33 100644
--- a/libc/startup/baremetal/fini.h
+++ b/libc/startup/baremetal/fini.h
@@ -6,7 +6,7 @@
//
//===----------------------------------------------------------------------===//
-#include <stdint.h>
+#include "hdr/stdint_proxy.h"
extern "C" {
extern uintptr_t __fini_array_start[];
diff --git a/libc/startup/baremetal/init.cpp b/libc/startup/baremetal/init.cpp
index 4d67fa84e557f..89065fd364ed9 100644
--- a/libc/startup/baremetal/init.cpp
+++ b/libc/startup/baremetal/init.cpp
@@ -6,7 +6,6 @@
//
//===----------------------------------------------------------------------===//
-#include "hdr/stdint_proxy.h"
#include "startup/baremetal/init.h"
#include "src/__support/macros/config.h"
diff --git a/libc/startup/baremetal/init.h b/libc/startup/baremetal/init.h
index 2b294e33c98e6..6b545db3976da 100644
--- a/libc/startup/baremetal/init.h
+++ b/libc/startup/baremetal/init.h
@@ -6,7 +6,7 @@
//
//===----------------------------------------------------------------------===//
-#include <stdint.h>
+#include "hdr/stdint_proxy.h"
extern "C" {
extern uintptr_t __preinit_array_start[];
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