[libc-commits] [libc] [libc] implement sys/getauxval (PR #78493)
Schrodinger ZHU Yifan via libc-commits
libc-commits at lists.llvm.org
Mon Jan 22 16:50:13 PST 2024
https://github.com/SchrodingerZhu updated https://github.com/llvm/llvm-project/pull/78493
>From 579c5ae0a3a91ff381828dd2839b94c20fb7e29c 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 01/10] [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 | 18 ++
libc/src/sys/auxv/linux/getauxval.cpp | 190 ++++++++++++++++++++++
10 files changed, 252 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 625fa6bffe63c6..3f66a582f5e3ee 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 c75ac2302d4ac4..301870d337ca00 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..b38d63ee0329c7
--- /dev/null
+++ b/libc/src/sys/auxv/linux/CMakeLists.txt
@@ -0,0 +1,18 @@
+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.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..b1d962698fe025
--- /dev/null
+++ b/libc/src/sys/auxv/linux/getauxval.cpp
@@ -0,0 +1,190 @@
+//===-- 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/common.h"
+#include "src/errno/libc_errno.h"
+#include <linux/auxvec.h>
+
+// for guarded initialization
+#include "src/__support/threads/callonce.h"
+#include "src/__support/threads/linux/futex_word.h"
+
+// for mallocing the global auxv
+#include "src/sys/mman/mmap.h"
+#include "src/sys/mman/munmap.h"
+
+// for reading /proc/self/auxv
+#include "src/fcntl/open.h"
+#include "src/sys/prctl/prctl.h"
+#include "src/unistd/close.h"
+#include "src/unistd/read.h"
+
+// getauxval will work either with or without atexit support.
+// In order to detect if atexit is supported, we define a weak symbol.
+extern "C" [[gnu::weak]] int atexit(void (*)(void));
+
+namespace LIBC_NAMESPACE {
+
+constexpr static size_t MAX_AUXV_ENTRIES = 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) * MAX_AUXV_ENTRIES;
+ 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) {
+ // if we cannot get atexit, we cannot register the cleanup function.
+ if (&atexit == nullptr)
+ return;
+
+ 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. MMAP private pages are zeroed out already.
+ 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 (available_size != 0) {
+ 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) -> AuxEntryType {
+ for (auto *ptr = auxv; ptr->id != AT_NULL; ptr++) {
+ if (ptr->id == id) {
+ return ptr->value;
+ }
+ }
+ errno_guard.mark_failure();
+ return AT_NULL;
+ };
+
+ // App is a weak symbol that is only defined if libc is linked to its own
+ // initialization routine. We need to check if it is null.
+ if (&app != nullptr) {
+ return search_auxv(app.auxv_ptr, id);
+ }
+
+ static 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
+ AuxvFdGuard fd_guard;
+ if (fd_guard.valid()) {
+ while (true) {
+ AuxEntry buf = read_entry(fd_guard.fd);
+ if (buf.id == AT_NULL)
+ break;
+ if (buf.id == id)
+ return buf.value;
+ }
+ }
+
+ // cannot find the entry after all methods, mark failure and return 0
+ errno_guard.mark_failure();
+ return AT_NULL;
+}
+} // namespace LIBC_NAMESPACE
>From 0e2fcff29f980500e3069d60926f65dd914da81c Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <yifanzhu at rochester.edu>
Date: Mon, 22 Jan 2024 14:24:43 -0500
Subject: [PATCH 02/10] fix bugs
---
libc/src/sys/auxv/linux/getauxval.cpp | 28 +++++++++++--------
libc/test/src/sys/CMakeLists.txt | 1 +
libc/test/src/sys/auxv/CMakeLists.txt | 3 ++
libc/test/src/sys/auxv/linux/CMakeLists.txt | 14 ++++++++++
.../src/sys/auxv/linux/getauxval_test.cpp | 27 ++++++++++++++++++
5 files changed, 62 insertions(+), 11 deletions(-)
create mode 100644 libc/test/src/sys/auxv/CMakeLists.txt
create mode 100644 libc/test/src/sys/auxv/linux/CMakeLists.txt
create mode 100644 libc/test/src/sys/auxv/linux/getauxval_test.cpp
diff --git a/libc/src/sys/auxv/linux/getauxval.cpp b/libc/src/sys/auxv/linux/getauxval.cpp
index b1d962698fe025..4b2aabe40c39b5 100644
--- a/libc/src/sys/auxv/linux/getauxval.cpp
+++ b/libc/src/sys/auxv/linux/getauxval.cpp
@@ -26,9 +26,12 @@
#include "src/unistd/close.h"
#include "src/unistd/read.h"
-// getauxval will work either with or without atexit support.
-// In order to detect if atexit is supported, we define a weak symbol.
-extern "C" [[gnu::weak]] int atexit(void (*)(void));
+// getauxval will work either with or without __cxa_atexit support.
+// In order to detect if __cxa_atexit is supported, we define a weak symbol.
+// We prefer __cxa_atexit as it is always defined as a C symbol whileas atexit
+// may not be created via objcopy yet.
+extern "C" [[gnu::weak]] int __cxa_atexit(void (*callback)(void *),
+ void *payload, void *);
namespace LIBC_NAMESPACE {
@@ -49,8 +52,9 @@ static AuxEntry *auxv = nullptr;
struct AuxvMMapGuard {
constexpr static size_t AUXV_MMAP_SIZE = sizeof(AuxEntry) * MAX_AUXV_ENTRIES;
void *ptr;
- AuxvMMapGuard(size_t size)
- : ptr(mmap(nullptr, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, -1, 0)) {}
+ AuxvMMapGuard()
+ : ptr(mmap(nullptr, AUXV_MMAP_SIZE, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0)) {}
~AuxvMMapGuard() {
if (ptr != MAP_FAILED) {
munmap(ptr, AUXV_MMAP_SIZE);
@@ -58,10 +62,12 @@ struct AuxvMMapGuard {
}
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;
- });
+ int ret = __cxa_atexit(
+ [](void *) {
+ munmap(auxv, AUXV_MMAP_SIZE);
+ auxv = nullptr;
+ },
+ nullptr, nullptr);
if (ret != 0)
return;
@@ -85,10 +91,10 @@ struct AuxvFdGuard {
static void initialize_auxv_once(void) {
// if we cannot get atexit, we cannot register the cleanup function.
- if (&atexit == nullptr)
+ if (&__cxa_atexit == nullptr)
return;
- AuxvMMapGuard mmap_guard(AuxvMMapGuard::AUXV_MMAP_SIZE);
+ AuxvMMapGuard mmap_guard;
if (!mmap_guard.allocated())
return;
auto *ptr = reinterpret_cast<AuxEntry *>(mmap_guard.ptr);
diff --git a/libc/test/src/sys/CMakeLists.txt b/libc/test/src/sys/CMakeLists.txt
index a87e77da7d2cdb..c7095456383b30 100644
--- a/libc/test/src/sys/CMakeLists.txt
+++ b/libc/test/src/sys/CMakeLists.txt
@@ -8,3 +8,4 @@ add_subdirectory(stat)
add_subdirectory(utsname)
add_subdirectory(wait)
add_subdirectory(prctl)
+add_subdirectory(auxv)
diff --git a/libc/test/src/sys/auxv/CMakeLists.txt b/libc/test/src/sys/auxv/CMakeLists.txt
new file mode 100644
index 00000000000000..b4bbe81c92ff2e
--- /dev/null
+++ b/libc/test/src/sys/auxv/CMakeLists.txt
@@ -0,0 +1,3 @@
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+ add_subdirectory(${LIBC_TARGET_OS})
+endif()
diff --git a/libc/test/src/sys/auxv/linux/CMakeLists.txt b/libc/test/src/sys/auxv/linux/CMakeLists.txt
new file mode 100644
index 00000000000000..c1e82a1f0a46c3
--- /dev/null
+++ b/libc/test/src/sys/auxv/linux/CMakeLists.txt
@@ -0,0 +1,14 @@
+add_custom_target(libc_sys_auxv_unittests)
+add_libc_unittest(
+ getauxval_test
+ SUITE
+ libc_sys_auxv_unittests
+ SRCS
+ getauxval_test.cpp
+ DEPENDS
+ libc.include.sys_auxv
+ libc.src.errno.errno
+ libc.src.sys.auxv.getauxval
+ libc.test.UnitTest.ErrnoSetterMatcher
+ libc.src.string.strstr
+)
diff --git a/libc/test/src/sys/auxv/linux/getauxval_test.cpp b/libc/test/src/sys/auxv/linux/getauxval_test.cpp
new file mode 100644
index 00000000000000..3b0c4e1b4175f2
--- /dev/null
+++ b/libc/test/src/sys/auxv/linux/getauxval_test.cpp
@@ -0,0 +1,27 @@
+//===-- Unittests for getaxuval -------------------------------------------===//
+//
+// 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/errno/libc_errno.h"
+#include "src/sys/auxv/getauxval.h"
+#include "test/UnitTest/ErrnoSetterMatcher.h"
+#include "test/UnitTest/Test.h"
+#include <src/string/strstr.h>
+#include <sys/auxv.h>
+
+using namespace LIBC_NAMESPACE::testing::ErrnoSetterMatcher;
+
+TEST(LlvmLibcGetauxvalTest, Basic) {
+ EXPECT_THAT(LIBC_NAMESPACE::getauxval(AT_PAGESZ), returns(GT(0ul)));
+ const char *filename;
+ auto getfilename = [&filename]() {
+ auto value = LIBC_NAMESPACE::getauxval(AT_EXECFN);
+ filename = reinterpret_cast<const char *>(value);
+ return value;
+ };
+ EXPECT_THAT(getfilename(), returns(NE(0ul)));
+ ASSERT_TRUE(LIBC_NAMESPACE::strstr(filename, "getauxval_test") != nullptr);
+}
>From 6ec61d7f95e600cd40bb829804c70ade25f4d757 Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <yifanzhu at rochester.edu>
Date: Mon, 22 Jan 2024 14:35:10 -0500
Subject: [PATCH 03/10] more comments
---
libc/src/sys/auxv/linux/getauxval.cpp | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/libc/src/sys/auxv/linux/getauxval.cpp b/libc/src/sys/auxv/linux/getauxval.cpp
index 4b2aabe40c39b5..dedd2c39119153 100644
--- a/libc/src/sys/auxv/linux/getauxval.cpp
+++ b/libc/src/sys/auxv/linux/getauxval.cpp
@@ -29,7 +29,9 @@
// getauxval will work either with or without __cxa_atexit support.
// In order to detect if __cxa_atexit is supported, we define a weak symbol.
// We prefer __cxa_atexit as it is always defined as a C symbol whileas atexit
-// may not be created via objcopy yet.
+// may not be created via objcopy yet. Also, for glibc, atexit is provided via
+// libc_nonshared.a rather than libc.so. So, it is may not be made ready for
+// overlay builds.
extern "C" [[gnu::weak]] int __cxa_atexit(void (*callback)(void *),
void *payload, void *);
>From 82dd9efdda2d1b9219275bd5b2735e0ae56c5a6e Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <yifanzhu at rochester.edu>
Date: Mon, 22 Jan 2024 16:29:51 -0500
Subject: [PATCH 04/10] address CR
---
libc/src/sys/auxv/linux/getauxval.cpp | 64 +++++++++++++++++----------
1 file changed, 40 insertions(+), 24 deletions(-)
diff --git a/libc/src/sys/auxv/linux/getauxval.cpp b/libc/src/sys/auxv/linux/getauxval.cpp
index dedd2c39119153..96c0a2ba814186 100644
--- a/libc/src/sys/auxv/linux/getauxval.cpp
+++ b/libc/src/sys/auxv/linux/getauxval.cpp
@@ -40,20 +40,24 @@ namespace LIBC_NAMESPACE {
constexpr static size_t MAX_AUXV_ENTRIES = 64;
// Helper to recover or set errno
-struct AuxvErrnoGuard {
- int saved;
- bool failure;
+class AuxvErrnoGuard {
+public:
AuxvErrnoGuard() : saved(libc_errno), failure(false) {}
~AuxvErrnoGuard() { libc_errno = failure ? ENOENT : saved; }
void mark_failure() { failure = true; }
+
+private:
+ int saved;
+ bool failure;
};
// Helper to manage the memory
static AuxEntry *auxv = nullptr;
-struct AuxvMMapGuard {
+class AuxvMMapGuard {
+public:
constexpr static size_t AUXV_MMAP_SIZE = sizeof(AuxEntry) * MAX_AUXV_ENTRIES;
- void *ptr;
+
AuxvMMapGuard()
: ptr(mmap(nullptr, AUXV_MMAP_SIZE, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0)) {}
@@ -77,29 +81,37 @@ struct AuxvMMapGuard {
auxv = reinterpret_cast<AuxEntry *>(ptr);
ptr = MAP_FAILED;
}
- bool allocated() { return ptr != MAP_FAILED; }
+ bool allocated() const { return ptr != MAP_FAILED; }
+ void *get() const { return ptr; }
+
+private:
+ void *ptr;
};
-struct AuxvFdGuard {
- int fd;
+class AuxvFdGuard {
+public:
AuxvFdGuard() : fd(open("/proc/self/auxv", O_RDONLY | O_CLOEXEC)) {}
~AuxvFdGuard() {
if (fd != -1) {
close(fd);
}
}
- bool valid() { return fd != -1; }
+ bool valid() const { return fd != -1; }
+ int get() const { return fd; }
+
+private:
+ int fd;
};
static void initialize_auxv_once(void) {
- // if we cannot get atexit, we cannot register the cleanup function.
+ // If we cannot get atexit, we cannot register the cleanup function.
if (&__cxa_atexit == nullptr)
return;
AuxvMMapGuard mmap_guard;
if (!mmap_guard.allocated())
return;
- auto *ptr = reinterpret_cast<AuxEntry *>(mmap_guard.ptr);
+ auto *ptr = reinterpret_cast<AuxEntry *>(mmap_guard.get());
// We get one less than the max size to make sure the search always
// terminates. MMAP private pages are zeroed out already.
@@ -118,16 +130,20 @@ static void initialize_auxv_once(void) {
auto *buf = reinterpret_cast<char *>(ptr);
libc_errno = 0;
bool error_detected = false;
+ // Read until we use up all the available space or we finish reading the file.
while (available_size != 0) {
- ssize_t bytes_read = read(fd_guard.fd, buf, available_size);
+ ssize_t bytes_read = read(fd_guard.get(), buf, available_size);
if (bytes_read <= 0) {
if (libc_errno == EINTR)
continue;
- error_detected = bytes_read < 0;
+ if (bytes_read == -1)
+ error_detected = true;
break;
}
+ buf += bytes_read;
available_size -= bytes_read;
}
+ // If we get out of the loop without an error, the auxv is ready.
if (!error_detected) {
mmap_guard.submit_to_global();
}
@@ -136,15 +152,18 @@ static void initialize_auxv_once(void) {
static AuxEntry read_entry(int fd) {
AuxEntry buf;
ssize_t size = sizeof(AuxEntry);
+ char *ptr = reinterpret_cast<char *>(&buf);
while (size > 0) {
- ssize_t ret = read(fd, &buf, size);
+ ssize_t ret = read(fd, ptr, size);
if (ret < 0) {
if (libc_errno == EINTR)
continue;
+ // Error detected, return AT_NULL
buf.id = AT_NULL;
buf.value = AT_NULL;
break;
}
+ ptr += ret;
size -= ret;
}
return buf;
@@ -158,32 +177,29 @@ LLVM_LIBC_FUNCTION(unsigned long, getauxval, (unsigned long id)) {
auto search_auxv = [&errno_guard](AuxEntry *auxv,
unsigned long id) -> AuxEntryType {
- for (auto *ptr = auxv; ptr->id != AT_NULL; ptr++) {
- if (ptr->id == id) {
+ for (auto *ptr = auxv; ptr->id != AT_NULL; ptr++)
+ if (ptr->id == id)
return ptr->value;
- }
- }
+
errno_guard.mark_failure();
return AT_NULL;
};
// App is a weak symbol that is only defined if libc is linked to its own
// initialization routine. We need to check if it is null.
- if (&app != nullptr) {
+ if (&app != nullptr)
return search_auxv(app.auxv_ptr, id);
- }
static FutexWordType once_flag;
callonce(reinterpret_cast<CallOnceFlag *>(&once_flag), initialize_auxv_once);
- if (auxv != nullptr) {
+ if (auxv != nullptr)
return search_auxv(auxv, id);
- }
- // fallback to use read without mmap
+ // Fallback to use read without mmap
AuxvFdGuard fd_guard;
if (fd_guard.valid()) {
while (true) {
- AuxEntry buf = read_entry(fd_guard.fd);
+ AuxEntry buf = read_entry(fd_guard.get());
if (buf.id == AT_NULL)
break;
if (buf.id == id)
>From 77e33b2a116226840167d80773717873dd15e6e8 Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <yifanzhu at rochester.edu>
Date: Mon, 22 Jan 2024 16:32:20 -0500
Subject: [PATCH 05/10] address CR
---
libc/src/sys/auxv/linux/getauxval.cpp | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/libc/src/sys/auxv/linux/getauxval.cpp b/libc/src/sys/auxv/linux/getauxval.cpp
index 96c0a2ba814186..27fb68f6860d2b 100644
--- a/libc/src/sys/auxv/linux/getauxval.cpp
+++ b/libc/src/sys/auxv/linux/getauxval.cpp
@@ -116,7 +116,11 @@ static void initialize_auxv_once(void) {
// We get one less than the max size to make sure the search always
// terminates. MMAP private pages are zeroed out already.
size_t available_size = AuxvMMapGuard::AUXV_MMAP_SIZE - sizeof(AuxEntryType);
-#if defined(PR_GET_AUXV)
+ // PR_GET_AUXV is only available on Linux kernel 6.1 and above. If this is not
+ // defined, we direcly fall back to reading /proc/self/auxv. In case the libc
+ // is compiled and run on separate kernels, we also check the return value of
+ // prctl.
+#ifdef(PR_GET_AUXV)
int ret = prctl(PR_GET_AUXV, reinterpret_cast<unsigned long>(ptr),
available_size, 0, 0);
if (ret >= 0) {
>From 93f2e7b3251b45f51b87187a9952fb074229cfd6 Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <yifanzhu at rochester.edu>
Date: Mon, 22 Jan 2024 16:35:15 -0500
Subject: [PATCH 06/10] address CR
---
libc/src/sys/auxv/linux/getauxval.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libc/src/sys/auxv/linux/getauxval.cpp b/libc/src/sys/auxv/linux/getauxval.cpp
index 27fb68f6860d2b..73520a422a1b2a 100644
--- a/libc/src/sys/auxv/linux/getauxval.cpp
+++ b/libc/src/sys/auxv/linux/getauxval.cpp
@@ -120,7 +120,7 @@ static void initialize_auxv_once(void) {
// defined, we direcly fall back to reading /proc/self/auxv. In case the libc
// is compiled and run on separate kernels, we also check the return value of
// prctl.
-#ifdef(PR_GET_AUXV)
+#ifdef PR_GET_AUXV
int ret = prctl(PR_GET_AUXV, reinterpret_cast<unsigned long>(ptr),
available_size, 0, 0);
if (ret >= 0) {
>From 117c5ccd88f2480ad224458e2254ec80d87cf3a4 Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <yifanzhu at rochester.edu>
Date: Mon, 22 Jan 2024 16:44:53 -0500
Subject: [PATCH 07/10] address CR
---
libc/src/sys/auxv/linux/getauxval.cpp | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/libc/src/sys/auxv/linux/getauxval.cpp b/libc/src/sys/auxv/linux/getauxval.cpp
index 73520a422a1b2a..1b31e70680c18f 100644
--- a/libc/src/sys/auxv/linux/getauxval.cpp
+++ b/libc/src/sys/auxv/linux/getauxval.cpp
@@ -148,9 +148,8 @@ static void initialize_auxv_once(void) {
available_size -= bytes_read;
}
// If we get out of the loop without an error, the auxv is ready.
- if (!error_detected) {
+ if (!error_detected)
mmap_guard.submit_to_global();
- }
}
static AuxEntry read_entry(int fd) {
>From 01013880ad6f426e2c88de64ed95dbdaeb908788 Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <yifanzhu at rochester.edu>
Date: Mon, 22 Jan 2024 16:49:23 -0500
Subject: [PATCH 08/10] clarify error_detected
---
libc/src/sys/auxv/linux/getauxval.cpp | 2 ++
1 file changed, 2 insertions(+)
diff --git a/libc/src/sys/auxv/linux/getauxval.cpp b/libc/src/sys/auxv/linux/getauxval.cpp
index 1b31e70680c18f..3018fa5c3ed192 100644
--- a/libc/src/sys/auxv/linux/getauxval.cpp
+++ b/libc/src/sys/auxv/linux/getauxval.cpp
@@ -140,6 +140,8 @@ static void initialize_auxv_once(void) {
if (bytes_read <= 0) {
if (libc_errno == EINTR)
continue;
+ // Now, we either have an non-recoverable error or we have reached the end
+ // of the file. Mark `error_detected` accordingly.
if (bytes_read == -1)
error_detected = true;
break;
>From 2a9758ab7e3135f94d380b0b03ff2b57e7b87933 Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <yifanzhu at rochester.edu>
Date: Mon, 22 Jan 2024 17:08:27 -0500
Subject: [PATCH 09/10] clean code style
---
libc/src/sys/auxv/linux/getauxval.cpp | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/libc/src/sys/auxv/linux/getauxval.cpp b/libc/src/sys/auxv/linux/getauxval.cpp
index 3018fa5c3ed192..b0db36732c06e1 100644
--- a/libc/src/sys/auxv/linux/getauxval.cpp
+++ b/libc/src/sys/auxv/linux/getauxval.cpp
@@ -62,9 +62,8 @@ class AuxvMMapGuard {
: ptr(mmap(nullptr, AUXV_MMAP_SIZE, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0)) {}
~AuxvMMapGuard() {
- if (ptr != MAP_FAILED) {
+ 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.
@@ -92,9 +91,8 @@ class AuxvFdGuard {
public:
AuxvFdGuard() : fd(open("/proc/self/auxv", O_RDONLY | O_CLOEXEC)) {}
~AuxvFdGuard() {
- if (fd != -1) {
+ if (fd != -1)
close(fd);
- }
}
bool valid() const { return fd != -1; }
int get() const { return fd; }
>From 83fcd4903903efd2038541877b7335cdfa20760b Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <yifanzhu at rochester.edu>
Date: Mon, 22 Jan 2024 19:49:55 -0500
Subject: [PATCH 10/10] fix UB
---
libc/test/src/sys/auxv/linux/getauxval_test.cpp | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/libc/test/src/sys/auxv/linux/getauxval_test.cpp b/libc/test/src/sys/auxv/linux/getauxval_test.cpp
index 3b0c4e1b4175f2..8811fd8dfbc3a4 100644
--- a/libc/test/src/sys/auxv/linux/getauxval_test.cpp
+++ b/libc/test/src/sys/auxv/linux/getauxval_test.cpp
@@ -15,13 +15,14 @@
using namespace LIBC_NAMESPACE::testing::ErrnoSetterMatcher;
TEST(LlvmLibcGetauxvalTest, Basic) {
- EXPECT_THAT(LIBC_NAMESPACE::getauxval(AT_PAGESZ), returns(GT(0ul)));
+ EXPECT_THAT(LIBC_NAMESPACE::getauxval(AT_PAGESZ),
+ returns(GT(0ul)).with_errno(EQ(0)));
const char *filename;
auto getfilename = [&filename]() {
auto value = LIBC_NAMESPACE::getauxval(AT_EXECFN);
filename = reinterpret_cast<const char *>(value);
return value;
};
- EXPECT_THAT(getfilename(), returns(NE(0ul)));
+ EXPECT_THAT(getfilename(), returns(NE(0ul)).with_errno(EQ(0)));
ASSERT_TRUE(LIBC_NAMESPACE::strstr(filename, "getauxval_test") != nullptr);
}
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