diff --git a/libc/bionic/grp_pwd.cpp b/libc/bionic/grp_pwd.cpp
index 078a0b3..2823662 100644
--- a/libc/bionic/grp_pwd.cpp
+++ b/libc/bionic/grp_pwd.cpp
@@ -467,7 +467,16 @@
 
 char* getlogin() { // NOLINT: implementing bad function.
   passwd *pw = getpwuid(getuid()); // NOLINT: implementing bad function in terms of bad function.
-  return (pw != NULL) ? pw->pw_name : NULL;
+  return pw ? pw->pw_name : nullptr;
+}
+
+int getlogin_r(char* buf, size_t size) {
+  char* login = getlogin();
+  if (login == nullptr) return errno;
+  size_t login_length = strlen(login) + 1;
+  if (login_length > size) return ERANGE;
+  memcpy(buf, login, login_length);
+  return 0;
 }
 
 void setpwent() {
diff --git a/libc/bionic/sysconf.cpp b/libc/bionic/sysconf.cpp
index 4a23fec..7325dbd 100644
--- a/libc/bionic/sysconf.cpp
+++ b/libc/bionic/sysconf.cpp
@@ -135,12 +135,12 @@
     case _SC_TIMERS:            return _POSIX_TIMERS;
     case _SC_GETGR_R_SIZE_MAX:  return 1024;
     case _SC_GETPW_R_SIZE_MAX:  return 1024;
-    case _SC_LOGIN_NAME_MAX:    return 256;   // Seems default on linux.
+    case _SC_LOGIN_NAME_MAX:    return LOGIN_NAME_MAX;
     case _SC_THREAD_DESTRUCTOR_ITERATIONS: return PTHREAD_DESTRUCTOR_ITERATIONS;
     case _SC_THREAD_KEYS_MAX:   return PTHREAD_KEYS_MAX;
     case _SC_THREAD_STACK_MIN:    return PTHREAD_STACK_MIN;
     case _SC_THREAD_THREADS_MAX:  return -1; // No specific limit.
-    case _SC_TTY_NAME_MAX:        return 32; // Seems default on linux.
+    case _SC_TTY_NAME_MAX:        return TTY_NAME_MAX;
     case _SC_THREADS:             return _POSIX_THREADS;
     case _SC_THREAD_ATTR_STACKADDR:   return _POSIX_THREAD_ATTR_STACKADDR;
     case _SC_THREAD_ATTR_STACKSIZE:   return _POSIX_THREAD_ATTR_STACKSIZE;
diff --git a/libc/include/limits.h b/libc/include/limits.h
index 157f7a6..51f4fad 100644
--- a/libc/include/limits.h
+++ b/libc/include/limits.h
@@ -137,6 +137,8 @@
 #include <bits/posix_limits.h>
 
 #define HOST_NAME_MAX _POSIX_HOST_NAME_MAX
+#define LOGIN_NAME_MAX 256
+#define TTY_NAME_MAX 32
 
 #define _POSIX_VERSION 200809L
 #define _POSIX2_VERSION _POSIX_VERSION
diff --git a/libc/include/unistd.h b/libc/include/unistd.h
index e024527..8336976 100644
--- a/libc/include/unistd.h
+++ b/libc/include/unistd.h
@@ -118,6 +118,7 @@
 int getresuid(uid_t* __ruid, uid_t* __euid, uid_t* __suid);
 int getresgid(gid_t* __rgid, gid_t* __egid, gid_t* __sgid);
 char* getlogin(void);
+int getlogin_r(char* __buffer, size_t __buffer_size) __INTRODUCED_IN_FUTURE;
 
 long fpathconf(int __fd, int __name);
 long pathconf(const char* __path, int __name);
diff --git a/libc/libc.arm.map b/libc/libc.arm.map
index a4212dd..45ca9eb 100644
--- a/libc/libc.arm.map
+++ b/libc/libc.arm.map
@@ -1316,6 +1316,11 @@
     wctrans_l; # introduced=26
 } LIBC_N;
 
+LIBC_P {
+  global:
+    getlogin_r; # future
+} LIBC_O;
+
 LIBC_PRIVATE {
   global:
     ___Unwind_Backtrace; # arm
@@ -1532,7 +1537,7 @@
     vfdprintf; # arm x86 mips
     wait3; # arm x86 mips
     wcswcs; # arm x86 mips
-} LIBC_O;
+} LIBC_P;
 
 LIBC_DEPRECATED {
   global:
@@ -1554,4 +1559,4 @@
     malloc_disable;
     malloc_enable;
     malloc_iterate;
-} LIBC_O;
+} LIBC_P;
diff --git a/libc/libc.arm64.map b/libc/libc.arm64.map
index bf0341a..ed1e82c 100644
--- a/libc/libc.arm64.map
+++ b/libc/libc.arm64.map
@@ -1238,6 +1238,11 @@
     wctrans_l; # introduced=26
 } LIBC_N;
 
+LIBC_P {
+  global:
+    getlogin_r; # future
+} LIBC_O;
+
 LIBC_PRIVATE {
   global:
     android_getaddrinfofornet;
@@ -1249,7 +1254,7 @@
     free_malloc_leak_info;
     get_malloc_leak_info;
     gMallocLeakZygoteChild;
-} LIBC_O;
+} LIBC_P;
 
 LIBC_DEPRECATED {
   global:
@@ -1271,4 +1276,4 @@
     malloc_disable;
     malloc_enable;
     malloc_iterate;
-} LIBC_O;
+} LIBC_P;
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index c271a57..8b1d6de 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -1341,6 +1341,11 @@
     wctrans_l; # introduced=26
 } LIBC_N;
 
+LIBC_P {
+  global:
+    getlogin_r; # future
+} LIBC_O;
+
 LIBC_PRIVATE {
   global:
     ___Unwind_Backtrace; # arm
@@ -1558,7 +1563,7 @@
     vfdprintf; # arm x86 mips
     wait3; # arm x86 mips
     wcswcs; # arm x86 mips
-} LIBC_O;
+} LIBC_P;
 
 LIBC_DEPRECATED {
   global:
@@ -1580,4 +1585,4 @@
     malloc_disable;
     malloc_enable;
     malloc_iterate;
-} LIBC_O;
+} LIBC_P;
diff --git a/libc/libc.mips.map b/libc/libc.mips.map
index 214c7f5..256ca9e 100644
--- a/libc/libc.mips.map
+++ b/libc/libc.mips.map
@@ -1300,6 +1300,11 @@
     wctrans_l; # introduced=26
 } LIBC_N;
 
+LIBC_P {
+  global:
+    getlogin_r; # future
+} LIBC_O;
+
 LIBC_PRIVATE {
   global:
     __accept4; # arm x86 mips
@@ -1373,7 +1378,7 @@
     vfdprintf; # arm x86 mips
     wait3; # arm x86 mips
     wcswcs; # arm x86 mips
-} LIBC_O;
+} LIBC_P;
 
 LIBC_DEPRECATED {
   global:
@@ -1395,4 +1400,4 @@
     malloc_disable;
     malloc_enable;
     malloc_iterate;
-} LIBC_O;
+} LIBC_P;
diff --git a/libc/libc.mips64.map b/libc/libc.mips64.map
index bf0341a..ed1e82c 100644
--- a/libc/libc.mips64.map
+++ b/libc/libc.mips64.map
@@ -1238,6 +1238,11 @@
     wctrans_l; # introduced=26
 } LIBC_N;
 
+LIBC_P {
+  global:
+    getlogin_r; # future
+} LIBC_O;
+
 LIBC_PRIVATE {
   global:
     android_getaddrinfofornet;
@@ -1249,7 +1254,7 @@
     free_malloc_leak_info;
     get_malloc_leak_info;
     gMallocLeakZygoteChild;
-} LIBC_O;
+} LIBC_P;
 
 LIBC_DEPRECATED {
   global:
@@ -1271,4 +1276,4 @@
     malloc_disable;
     malloc_enable;
     malloc_iterate;
-} LIBC_O;
+} LIBC_P;
diff --git a/libc/libc.x86.map b/libc/libc.x86.map
index 145b64e..2ebc86c 100644
--- a/libc/libc.x86.map
+++ b/libc/libc.x86.map
@@ -1298,6 +1298,11 @@
     wctrans_l; # introduced=26
 } LIBC_N;
 
+LIBC_P {
+  global:
+    getlogin_r; # future
+} LIBC_O;
+
 LIBC_PRIVATE {
   global:
     __accept4; # arm x86 mips
@@ -1372,7 +1377,7 @@
     vfdprintf; # arm x86 mips
     wait3; # arm x86 mips
     wcswcs; # arm x86 mips
-} LIBC_O;
+} LIBC_P;
 
 LIBC_DEPRECATED {
   global:
@@ -1394,4 +1399,4 @@
     malloc_disable;
     malloc_enable;
     malloc_iterate;
-} LIBC_O;
+} LIBC_P;
diff --git a/libc/libc.x86_64.map b/libc/libc.x86_64.map
index bf0341a..ed1e82c 100644
--- a/libc/libc.x86_64.map
+++ b/libc/libc.x86_64.map
@@ -1238,6 +1238,11 @@
     wctrans_l; # introduced=26
 } LIBC_N;
 
+LIBC_P {
+  global:
+    getlogin_r; # future
+} LIBC_O;
+
 LIBC_PRIVATE {
   global:
     android_getaddrinfofornet;
@@ -1249,7 +1254,7 @@
     free_malloc_leak_info;
     get_malloc_leak_info;
     gMallocLeakZygoteChild;
-} LIBC_O;
+} LIBC_P;
 
 LIBC_DEPRECATED {
   global:
@@ -1271,4 +1276,4 @@
     malloc_disable;
     malloc_enable;
     malloc_iterate;
-} LIBC_O;
+} LIBC_P;