Auto merge of #2156 - niluxv:add_explicit_memset_functions, r=JohnTitor

Add explicit/volatile memset/memzero functions

Adds the following functions to platforms that support them:
* `explicit_bzero` (de facto standard): Glibc, MUSL, FreeBSD, DragonFly BSD, OpenBSD
* `explicit_memset`: NetBSD
* `memset_s` (C11 standard): FreeBSD, DragonFly BSD, Apple OSX

These functions are useful for zeroing secret memory.

Closes #2009

Author: bors

libc-test/semver/apple.txt

@@ -1619,6 +1619,7 @@ mach_timebase_info_data_t
 madvise
 max_align_t
 mcontext_t
+memset_s
 mincore
 mkdirat
 mkstemps

libc-test/semver/dragonfly.txt

@@ -1174,6 +1174,7 @@ endpwent
 endservent
 endutxent
 exit_status
+explicit_bzero
 faccessat
 fchdir
 fchflags
@@ -1243,6 +1244,7 @@ lwpid_t
 madvise
 memmem
 memrchr
+memset_s
 mincore
 mkdirat
 mkfifoat

libc-test/semver/freebsd.txt

@@ -1350,6 +1350,7 @@ endgrent
 endpwent
 endservent
 endutxent
+explicit_bzero
 extattr_delete_fd
 extattr_delete_file
 extattr_delete_link
@@ -1442,6 +1443,7 @@ lwpid_t
 madvise
 memmem
 memrchr
+memset_s
 mincore
 mkdirat
 mkfifoat

libc-test/semver/linux-gnu.txt

@@ -529,6 +529,7 @@ copy_file_range
 dlinfo
 dlmopen
 endutxent
+explicit_bzero
 fgetspent_r
 getgrent_r
 getpt

libc-test/semver/linux-musl.txt

@@ -1 +1,2 @@
 # TODO: musl.
+explicit_bzero

libc-test/semver/netbsd.txt

@@ -1034,6 +1034,7 @@ endpwent
 endservent
 endutent
 endutxent
+explicit_memset
 extattr_delete_fd
 extattr_delete_file
 extattr_delete_link

libc-test/semver/openbsd.txt

@@ -899,6 +899,7 @@ endgrent
 endpwent
 endservent
 execvpe
+explicit_bzero
 export_args
 faccessat
 fchdir

src/unix/bsd/apple/mod.rs

@@ -3877,6 +3877,10 @@ extern "C" {
         dst: *const ::c_char,
         flags: u32,
     ) -> ::c_int;
+
+    // Added in macOS 10.13
+    // ISO/IEC 9899:2011 ("ISO C11") K.3.7.4.1
+    pub fn memset_s(s: *mut ::c_void, smax: ::size_t, c: ::c_int, n: ::size_t) -> ::c_int;
 }
 
 #[link(name = "iconv")]

src/unix/bsd/freebsdlike/mod.rs

@@ -1591,6 +1591,12 @@ extern "C" {
         outbytesleft: *mut ::size_t,
     ) -> ::size_t;
     pub fn iconv_close(cd: iconv_t) -> ::c_int;
+
+    // Added in `FreeBSD` 11.0
+    // Added in `DragonFly BSD` 5.4
+    pub fn explicit_bzero(s: *mut ::c_void, len: ::size_t);
+    // ISO/IEC 9899:2011 ("ISO C11") K.3.7.4.1
+    pub fn memset_s(s: *mut ::c_void, smax: ::size_t, c: ::c_int, n: ::size_t) -> ::c_int;
 }
 
 #[link(name = "rt")]

src/unix/bsd/netbsdlike/netbsd/mod.rs

@@ -2083,6 +2083,9 @@ extern "C" {
         outbytesleft: *mut ::size_t,
     ) -> ::size_t;
     pub fn iconv_close(cd: iconv_t) -> ::c_int;
+
+    // Added in `NetBSD` 7.0
+    pub fn explicit_memset(b: *mut ::c_void, c: ::c_int, len: ::size_t);
 }
 
 #[link(name = "util")]

src/unix/bsd/netbsdlike/openbsd/mod.rs

@@ -1544,6 +1544,9 @@ extern "C" {
     pub fn freelocale(loc: ::locale_t);
     pub fn newlocale(mask: ::c_int, locale: *const ::c_char, base: ::locale_t) -> ::locale_t;
     pub fn duplocale(base: ::locale_t) -> ::locale_t;
+
+    // Added in `OpenBSD` 5.5
+    pub fn explicit_bzero(s: *mut ::c_void, len: ::size_t);
 }
 
 cfg_if! {

src/unix/linux_like/linux/gnu/mod.rs

@@ -1233,6 +1233,9 @@ extern "C" {
         newpath: *const ::c_char,
         flags: ::c_uint,
     ) -> ::c_int;
+
+    // Added in `glibc` 2.25
+    pub fn explicit_bzero(s: *mut ::c_void, len: ::size_t);
 }
 
 extern "C" {

src/unix/linux_like/linux/musl/mod.rs

@@ -697,6 +697,9 @@ extern "C" {
         path: *const ::c_char,
     ) -> ::c_int;
     pub fn getauxval(type_: ::c_ulong) -> ::c_ulong;
+
+    // Added in `musl` 1.1.20
+    pub fn explicit_bzero(s: *mut ::c_void, len: ::size_t);
 }
 
 cfg_if! {