[libc-commits] [libc] [libc] Basic implementation of crt0 (PR #146863)

[Michael Jones via libc-commits]

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@@ -0,0 +1,92 @@
+//===-- 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.
+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"
+
+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);
----------------
michaelrj-google wrote:

explicitly use the namespace on `memcpy` and `memset`
```suggestion
  LIBC_NAMESPACE::memcpy(__data_start, __data_source, (uintptr_t)__data_size);
  LIBC_NAMESPACE::memset(__bss_start, '\0', (uintptr_t)__bss_size);
```

https://github.com/llvm/llvm-project/pull/146863