[libc-commits] [libc] [libc] major refactor of startup library (PR #76092)
via libc-commits
libc-commits at lists.llvm.org
Thu Dec 21 15:56:50 PST 2023
================
@@ -1,151 +1,20 @@
-//===-- Implementation of crt for x86_64 ----------------------------------===//
+//===-- Implementation of _start for x86_64 -------------------------------===//
//
// 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 "config/linux/app.h"
-#include "src/__support/OSUtil/io.h"
-#include "src/__support/OSUtil/syscall.h"
-#include "src/__support/threads/thread.h"
-#include "src/stdlib/abort.h"
-#include "src/stdlib/atexit.h"
-#include "src/stdlib/exit.h"
-#include "src/string/memory_utils/inline_memcpy.h"
-
-#include <asm/prctl.h>
-#include <linux/auxvec.h>
-#include <linux/elf.h>
-#include <stdint.h>
-#include <sys/mman.h>
-#include <sys/syscall.h>
-#include <unistd.h>
-
-extern "C" int main(int, char **, char **);
-
-namespace LIBC_NAMESPACE {
-
-#ifdef SYS_mmap2
-static constexpr long MMAP_SYSCALL_NUMBER = SYS_mmap2;
-#elif SYS_mmap
-static constexpr long MMAP_SYSCALL_NUMBER = SYS_mmap;
-#else
-#error "mmap and mmap2 syscalls not available."
-#endif
-
-AppProperties app;
-
-static ThreadAttributes main_thread_attrib;
-
-// TODO: The function is x86_64 specific. Move it to config/linux/app.h
-// and generalize it. Also, dynamic loading is not handled currently.
-void init_tls(TLSDescriptor &tls_descriptor) {
- if (app.tls.size == 0) {
- tls_descriptor.size = 0;
- tls_descriptor.tp = 0;
- return;
- }
-
- // We will assume the alignment is always a power of two.
- uintptr_t tls_size = app.tls.size & -app.tls.align;
- if (tls_size != app.tls.size)
- tls_size += app.tls.align;
-
- // Per the x86_64 TLS ABI, the entry pointed to by the thread pointer is the
- // address of the TLS block. So, we add more size to accomodate this address
- // entry.
- // We also need to include space for the stack canary. The canary is at
- // offset 0x28 (40) and is of size uintptr_t.
- uintptr_t tls_size_with_addr = tls_size + sizeof(uintptr_t) + 40;
-
- // We cannot call the mmap function here as the functions set errno on
- // failure. Since errno is implemented via a thread local variable, we cannot
- // use errno before TLS is setup.
- long mmap_retval = LIBC_NAMESPACE::syscall_impl<long>(
- MMAP_SYSCALL_NUMBER, nullptr, tls_size_with_addr, PROT_READ | PROT_WRITE,
- MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
- // We cannot check the return value with MAP_FAILED as that is the return
- // of the mmap function and not the mmap syscall.
- if (mmap_retval < 0 && static_cast<uintptr_t>(mmap_retval) > -app.page_size)
- LIBC_NAMESPACE::syscall_impl<long>(SYS_exit, 1);
- uintptr_t *tls_addr = reinterpret_cast<uintptr_t *>(mmap_retval);
-
- // x86_64 TLS faces down from the thread pointer with the first entry
- // pointing to the address of the first real TLS byte.
- uintptr_t end_ptr = reinterpret_cast<uintptr_t>(tls_addr) + tls_size;
- *reinterpret_cast<uintptr_t *>(end_ptr) = end_ptr;
-
- LIBC_NAMESPACE::inline_memcpy(reinterpret_cast<char *>(tls_addr),
- reinterpret_cast<const char *>(app.tls.address),
- app.tls.init_size);
- uintptr_t *stack_guard_addr = reinterpret_cast<uintptr_t *>(end_ptr + 40);
- // Setting the stack guard to a random value.
- // We cannot call the get_random function here as the function sets errno on
- // failure. Since errno is implemented via a thread local variable, we cannot
- // use errno before TLS is setup.
- ssize_t stack_guard_retval = LIBC_NAMESPACE::syscall_impl<ssize_t>(
- SYS_getrandom, reinterpret_cast<long>(stack_guard_addr), sizeof(uint64_t),
- 0);
- if (stack_guard_retval < 0)
- LIBC_NAMESPACE::syscall_impl(SYS_exit, 1);
-
- tls_descriptor = {tls_size_with_addr, reinterpret_cast<uintptr_t>(tls_addr),
- end_ptr};
- return;
-}
-
-void cleanup_tls(uintptr_t addr, uintptr_t size) {
- if (size == 0)
- return;
- LIBC_NAMESPACE::syscall_impl<long>(SYS_munmap, addr, size);
-}
-
-// Sets the thread pointer to |val|. Returns true on success, false on failure.
-static bool set_thread_ptr(uintptr_t val) {
- return LIBC_NAMESPACE::syscall_impl(SYS_arch_prctl, ARCH_SET_FS, val) != -1;
-}
-
-using InitCallback = void(int, char **, char **);
-using FiniCallback = void(void);
-
-extern "C" {
-// These arrays are present in the .init_array and .fini_array sections.
-// The symbols are inserted by linker when it sees references to them.
-extern uintptr_t __preinit_array_start[];
-extern uintptr_t __preinit_array_end[];
-extern uintptr_t __init_array_start[];
-extern uintptr_t __init_array_end[];
-extern uintptr_t __fini_array_start[];
-extern uintptr_t __fini_array_end[];
-}
-
-static void call_init_array_callbacks(int argc, char **argv, char **env) {
- size_t preinit_array_size = __preinit_array_end - __preinit_array_start;
- for (size_t i = 0; i < preinit_array_size; ++i)
- reinterpret_cast<InitCallback *>(__preinit_array_start[i])(argc, argv, env);
- size_t init_array_size = __init_array_end - __init_array_start;
- for (size_t i = 0; i < init_array_size; ++i)
- reinterpret_cast<InitCallback *>(__init_array_start[i])(argc, argv, env);
-}
-
-static void call_fini_array_callbacks() {
- size_t fini_array_size = __fini_array_end - __fini_array_start;
- for (size_t i = fini_array_size; i > 0; --i)
- reinterpret_cast<FiniCallback *>(__fini_array_start[i - 1])();
-}
-
-} // namespace LIBC_NAMESPACE
-
-using LIBC_NAMESPACE::app;
-using LIBC_NAMESPACE::AuxEntry;
-
-extern "C" void _start() {
- // This TU is compiled with -fno-omit-frame-pointer. Hence, the previous value
- // of the base pointer is pushed on to the stack. So, we step over it (the
+#include "src/__support/macros/attributes.h"
+#include "startup/linux/do_start.h"
+
+extern "C" [[noreturn]] void _start() {
+ using namespace LIBC_NAMESPACE;
+ // This TU is compiled with -fno-omit-frame-pointer. Hence, the previous
+ // value of the base pointer is pushed on to the stack. So, we step over
+ // it (the
----------------
michaelrj-google wrote:
nit: this comment doesn't need to spill onto the next line anymore.
https://github.com/llvm/llvm-project/pull/76092
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