Add C23's memset_explicit().
https://open-std.org/jtc1/sc22/wg14/www/docs/n2897.htm
Test: treehugger
Change-Id: Ia0cfc72bdf3c22eda6a4fc9adaa4c0ca0ff9a7c8
diff --git a/docs/status.md b/docs/status.md
index d509e41..0aca544 100644
--- a/docs/status.md
+++ b/docs/status.md
@@ -53,6 +53,7 @@
New libc functions in U (API level 34):
* `close_range` and `copy_file_range` (Linux-specific GNU extensions).
+ * `memset_explicit` in <string.h> (C23 addition).
New libc behavior in U (API level 34):
* Support for `%b` and `%B` in the printf and wprintf family.
diff --git a/libc/Android.bp b/libc/Android.bp
index b7cb59d..aef6090 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -1110,6 +1110,7 @@
"bionic/mbrtoc16.cpp",
"bionic/mbrtoc32.cpp",
"bionic/mempcpy.cpp",
+ "bionic/memset_explicit.cpp",
"bionic/mkdir.cpp",
"bionic/mkfifo.cpp",
"bionic/mknod.cpp",
diff --git a/libc/bionic/memset_explicit.cpp b/libc/bionic/memset_explicit.cpp
new file mode 100644
index 0000000..2bcc20c
--- /dev/null
+++ b/libc/bionic/memset_explicit.cpp
@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <string.h>
+
+void* memset_explicit(void* __dst, int __ch, size_t __n) {
+ void* result = memset(__dst, __ch, __n);
+ // https://bugs.llvm.org/show_bug.cgi?id=15495
+ __asm__ __volatile__("" : : "r"(__dst) : "memory");
+ return result;
+}
diff --git a/libc/include/string.h b/libc/include/string.h
index 0cc5611..59c4687 100644
--- a/libc/include/string.h
+++ b/libc/include/string.h
@@ -55,7 +55,24 @@
void* mempcpy(void* __dst, const void* __src, size_t __n) __INTRODUCED_IN(23);
#endif
void* memmove(void* __dst, const void* __src, size_t __n);
+
+/**
+ * [memset(3)](http://man7.org/linux/man-pages/man3/memset.3.html) writes the
+ * bottom 8 bits of the given int to the next `n` bytes of `dst`.
+ *
+ * Returns `dst`.
+ */
void* memset(void* __dst, int __ch, size_t __n);
+
+/**
+ * [memset_explicit(3)](http://man7.org/linux/man-pages/man3/memset_explicit.3.html)
+ * writes the bottom 8 bits of the given int to the next `n` bytes of `dst`,
+ * but won't be optimized out by the compiler.
+ *
+ * Returns `dst`.
+ */
+void* memset_explicit(void* __dst, int __ch, size_t __n) __INTRODUCED_IN(34);
+
void* memmem(const void* __haystack, size_t __haystack_size, const void* __needle, size_t __needle_size) __attribute_pure__;
char* strchr(const char* __s, int __ch) __attribute_pure__;
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index 79f331a..0f41878 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -1580,6 +1580,7 @@
global:
close_range;
copy_file_range;
+ memset_explicit;
} LIBC_T;
LIBC_PRIVATE {
diff --git a/tests/string_test.cpp b/tests/string_test.cpp
index 8d3fb68..30c87dc 100644
--- a/tests/string_test.cpp
+++ b/tests/string_test.cpp
@@ -1673,3 +1673,15 @@
ASSERT_EQ(nullptr, memccpy(dst, "hello world", ' ', 4));
ASSERT_STREQ("hell", dst);
}
+
+TEST(STRING_TEST, memset_explicit_smoke) {
+#if defined(__BIONIC__)
+ // We can't reliably test that the compiler won't optimize out calls to
+ // memset_explicit(), but we can at least check that it behaves like memset.
+ char buf[32];
+ memset_explicit(buf, 'x', sizeof(buf));
+ ASSERT_TRUE(memcmp(buf, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx", sizeof(buf)) == 0);
+#else
+ GTEST_SKIP() << "memset_explicit not available";
+#endif
+}