[libc-commits] [libc] [libc] implement sys/getauxval (PR #78493)
Schrodinger ZHU Yifan via libc-commits
libc-commits at lists.llvm.org
Wed Jan 17 11:31:51 PST 2024
https://github.com/SchrodingerZhu created https://github.com/llvm/llvm-project/pull/78493
None
>From 047864138a4a1b227998121d79d80e62d60a362f Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <yifanzhu at rochester.edu>
Date: Tue, 19 Dec 2023 00:39:04 -0500
Subject: [PATCH] [libc] implement sys/getauxval
---
libc/config/linux/aarch64/entrypoints.txt | 3 +
libc/config/linux/app.h | 2 +-
libc/config/linux/arm/entrypoints.txt | 3 +
libc/config/linux/riscv/entrypoints.txt | 3 +
libc/config/linux/x86_64/entrypoints.txt | 3 +
libc/src/sys/CMakeLists.txt | 1 +
libc/src/sys/auxv/CMakeLists.txt | 10 ++
libc/src/sys/auxv/getauxval.h | 20 +++
libc/src/sys/auxv/linux/CMakeLists.txt | 19 +++
libc/src/sys/auxv/linux/getauxval.cpp | 176 ++++++++++++++++++++++
10 files changed, 239 insertions(+), 1 deletion(-)
create mode 100644 libc/src/sys/auxv/CMakeLists.txt
create mode 100644 libc/src/sys/auxv/getauxval.h
create mode 100644 libc/src/sys/auxv/linux/CMakeLists.txt
create mode 100644 libc/src/sys/auxv/linux/getauxval.cpp
diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index ab54633006979b..37197a26e16d69 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -168,6 +168,9 @@ set(TARGET_LIBC_ENTRYPOINTS
# sys/prctl.h entrypoints
libc.src.sys.prctl.prctl
+ # sys/auxv.h entrypoints
+ libc.src.sys.auxv.getauxval
+
# termios.h entrypoints
libc.src.termios.cfgetispeed
libc.src.termios.cfgetospeed
diff --git a/libc/config/linux/app.h b/libc/config/linux/app.h
index 1b3523deb1b23e..766cd49e88f6f7 100644
--- a/libc/config/linux/app.h
+++ b/libc/config/linux/app.h
@@ -93,7 +93,7 @@ struct AppProperties {
AuxEntry *auxv_ptr;
};
-extern AppProperties app;
+[[gnu::weak]] extern AppProperties app;
// The descriptor of a thread's TLS area.
struct TLSDescriptor {
diff --git a/libc/config/linux/arm/entrypoints.txt b/libc/config/linux/arm/entrypoints.txt
index 274d5aa5a0057d..5bcf86a8063e26 100644
--- a/libc/config/linux/arm/entrypoints.txt
+++ b/libc/config/linux/arm/entrypoints.txt
@@ -95,6 +95,9 @@ set(TARGET_LIBC_ENTRYPOINTS
# sys/prctl.h entrypoints
libc.src.sys.prctl.prctl
+
+ # sys/auxv.h entrypoints
+ libc.src.sys.auxv.getauxval
)
set(TARGET_LIBM_ENTRYPOINTS
diff --git a/libc/config/linux/riscv/entrypoints.txt b/libc/config/linux/riscv/entrypoints.txt
index ec2a16f5cf473b..0331ef782cf74a 100644
--- a/libc/config/linux/riscv/entrypoints.txt
+++ b/libc/config/linux/riscv/entrypoints.txt
@@ -174,6 +174,9 @@ set(TARGET_LIBC_ENTRYPOINTS
# sys/prctl.h entrypoints
libc.src.sys.prctl.prctl
+ # sys/auxv.h entrypoints
+ libc.src.sys.auxv.getauxval
+
# termios.h entrypoints
libc.src.termios.cfgetispeed
libc.src.termios.cfgetospeed
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 094bdde2e1589c..d5ab891674a2d8 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -174,6 +174,9 @@ set(TARGET_LIBC_ENTRYPOINTS
# sys/prctl.h entrypoints
libc.src.sys.prctl.prctl
+ # sys/auxv.h entrypoints
+ libc.src.sys.auxv.getauxval
+
# termios.h entrypoints
libc.src.termios.cfgetispeed
libc.src.termios.cfgetospeed
diff --git a/libc/src/sys/CMakeLists.txt b/libc/src/sys/CMakeLists.txt
index 12e2020f013ab1..81098294176ad5 100644
--- a/libc/src/sys/CMakeLists.txt
+++ b/libc/src/sys/CMakeLists.txt
@@ -1,3 +1,4 @@
+add_subdirectory(auxv)
add_subdirectory(mman)
add_subdirectory(random)
add_subdirectory(resource)
diff --git a/libc/src/sys/auxv/CMakeLists.txt b/libc/src/sys/auxv/CMakeLists.txt
new file mode 100644
index 00000000000000..4065761064b129
--- /dev/null
+++ b/libc/src/sys/auxv/CMakeLists.txt
@@ -0,0 +1,10 @@
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+ add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+endif()
+
+add_entrypoint_object(
+ getauxval
+ ALIAS
+ DEPENDS
+ .${LIBC_TARGET_OS}.getauxval
+)
diff --git a/libc/src/sys/auxv/getauxval.h b/libc/src/sys/auxv/getauxval.h
new file mode 100644
index 00000000000000..7c9fb846e91984
--- /dev/null
+++ b/libc/src/sys/auxv/getauxval.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for getauxval function ------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SYS_AUXV_GETAUXVAL_H
+#define LLVM_LIBC_SRC_SYS_AUXV_GETAUXVAL_H
+
+#include <sys/auxv.h>
+
+namespace LIBC_NAMESPACE {
+
+unsigned long getauxval(unsigned long id);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_SYS_AUXV_GETAUXVAL_H
diff --git a/libc/src/sys/auxv/linux/CMakeLists.txt b/libc/src/sys/auxv/linux/CMakeLists.txt
new file mode 100644
index 00000000000000..f57100e422cb93
--- /dev/null
+++ b/libc/src/sys/auxv/linux/CMakeLists.txt
@@ -0,0 +1,19 @@
+add_entrypoint_object(
+ getauxval
+ SRCS
+ getauxval.cpp
+ HDRS
+ ../getauxval.h
+ DEPENDS
+ libc.src.sys.prctl.prctl
+ libc.src.sys.mman.mmap
+ libc.src.sys.mman.munmap
+ libc.src.__support.threads.callonce
+ libc.src.__support.common
+ libc.src.errno.errno
+ libc.src.stdlib.atexit
+ libc.config.linux.app_h
+ libc.src.fcntl.open
+ libc.src.unistd.read
+ libc.src.unistd.close
+)
diff --git a/libc/src/sys/auxv/linux/getauxval.cpp b/libc/src/sys/auxv/linux/getauxval.cpp
new file mode 100644
index 00000000000000..9558aa903fb7e3
--- /dev/null
+++ b/libc/src/sys/auxv/linux/getauxval.cpp
@@ -0,0 +1,176 @@
+//===-- Implementation file for getauxval function --------------*- C++ -*-===//
+//
+// 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/sys/auxv/getauxval.h"
+#include "config/linux/app.h"
+#include "src/__support/CPP/atomic.h"
+#include "src/__support/common.h"
+#include "src/__support/threads/callonce.h"
+#include "src/__support/threads/linux/futex_word.h"
+#include "src/errno/libc_errno.h"
+#include "src/fcntl/open.h"
+#include "src/stdlib/atexit.h"
+#include "src/sys/mman/mmap.h"
+#include "src/sys/mman/munmap.h"
+#include "src/sys/prctl/prctl.h"
+#include "src/unistd/close.h"
+#include "src/unistd/read.h"
+#include <linux/auxvec.h>
+
+namespace LIBC_NAMESPACE {
+
+constexpr static size_t AUXV_SIZE = 64;
+
+// Helper to recover or set errno
+struct AuxvErrnoGuard {
+ int saved;
+ bool failure;
+ AuxvErrnoGuard() : saved(libc_errno), failure(false) {}
+ ~AuxvErrnoGuard() { libc_errno = failure ? ENOENT : saved; }
+ void mark_failure() { failure = true; }
+};
+
+// Helper to manage the memory
+static AuxEntry *auxv = nullptr;
+
+struct AuxvMMapGuard {
+ constexpr static size_t AUXV_MMAP_SIZE = sizeof(AuxEntry) * AUXV_SIZE;
+ void *ptr;
+ AuxvMMapGuard(size_t size)
+ : ptr(mmap(nullptr, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, -1, 0)) {}
+ ~AuxvMMapGuard() {
+ if (ptr != MAP_FAILED) {
+ munmap(ptr, AUXV_MMAP_SIZE);
+ }
+ }
+ void submit_to_global() {
+ // atexit may fail, we do not set it to global in that case.
+ int ret = atexit([]() {
+ munmap(auxv, AUXV_MMAP_SIZE);
+ auxv = nullptr;
+ });
+
+ if (ret != 0)
+ return;
+
+ auxv = reinterpret_cast<AuxEntry *>(ptr);
+ ptr = MAP_FAILED;
+ }
+ bool allocated() { return ptr != MAP_FAILED; }
+};
+
+struct AuxvFdGuard {
+ int fd;
+ AuxvFdGuard() : fd(open("/proc/self/auxv", O_RDONLY | O_CLOEXEC)) {}
+ ~AuxvFdGuard() {
+ if (fd != -1) {
+ close(fd);
+ }
+ }
+ bool valid() { return fd != -1; }
+};
+
+static void initialize_auxv_once(void) {
+ AuxvMMapGuard mmap_guard(AuxvMMapGuard::AUXV_MMAP_SIZE);
+ if (!mmap_guard.allocated())
+ return;
+ auto *ptr = reinterpret_cast<AuxEntry *>(mmap_guard.ptr);
+ // we get one less than the max size to make sure the search always
+ // terminates.
+ size_t available_size = AuxvMMapGuard::AUXV_MMAP_SIZE - sizeof(AuxEntryType);
+#if defined(PR_GET_AUXV)
+ int ret = prctl(PR_GET_AUXV, reinterpret_cast<unsigned long>(ptr),
+ available_size, 0, 0);
+ if (ret >= 0) {
+ mmap_guard.submit_to_global();
+ return;
+ }
+#endif
+ AuxvFdGuard fd_guard;
+ if (!fd_guard.valid())
+ return;
+ auto *buf = reinterpret_cast<char *>(ptr);
+ libc_errno = 0;
+ bool error_detected = false;
+ while (true) {
+ ssize_t bytes_read = read(fd_guard.fd, buf, available_size);
+ if (bytes_read <= 0) {
+ if (libc_errno == EINTR)
+ continue;
+ error_detected = bytes_read < 0;
+ break;
+ }
+ available_size -= bytes_read;
+ }
+ if (!error_detected) {
+ mmap_guard.submit_to_global();
+ }
+}
+
+static AuxEntry read_entry(int fd) {
+ AuxEntry buf;
+ ssize_t size = sizeof(AuxEntry);
+ while (size > 0) {
+ ssize_t ret = read(fd, &buf, size);
+ if (ret < 0) {
+ if (libc_errno == EINTR)
+ continue;
+ buf.id = AT_NULL;
+ buf.value = AT_NULL;
+ break;
+ }
+ size -= ret;
+ }
+ return buf;
+}
+
+LLVM_LIBC_FUNCTION(unsigned long, getauxval, (unsigned long id)) {
+ // Fast path when libc is loaded by its own initialization code. In this case,
+ // app.auxv_ptr is already set to the auxv passed on the initial stack of the
+ // process.
+ AuxvErrnoGuard errno_guard;
+
+ auto search_auxv = [&errno_guard](AuxEntry *auxv, unsigned long id) {
+ for (auto *ptr = auxv; ptr->id != AT_NULL; ptr++) {
+ if (ptr->id == id) {
+ return ptr->value;
+ }
+ }
+ errno_guard.mark_failure();
+ return AuxEntryType{0};
+ };
+
+ if (&app != nullptr) {
+ return search_auxv(app.auxv_ptr, id);
+ }
+
+ static cpp::Atomic<FutexWordType> once_flag;
+ callonce(reinterpret_cast<CallOnceFlag *>(&once_flag), initialize_auxv_once);
+ if (auxv != nullptr) {
+ return search_auxv(auxv, id);
+ }
+
+ // fallback to use read without mmap
+ do {
+ AuxvFdGuard fd_guard;
+ if (!fd_guard.valid())
+ break;
+
+ while (true) {
+ AuxEntry buf = read_entry(fd_guard.fd);
+ if (buf.id == AT_NULL)
+ break;
+ if (buf.id == id)
+ return buf.value;
+ }
+
+ } while (0);
+ errno_guard.mark_failure();
+ return 0;
+}
+} // namespace LIBC_NAMESPACE
More information about the libc-commits
mailing list