[libc-commits] [libc] [libc] Independent strcat/strncat/stpcpy (PR #142643)

[Michael Jones via libc-commits]

https://github.com/michaelrj-google updated https://github.com/llvm/llvm-project/pull/142643

>From ac9675fdf59a43653035925d4697ea4055d29298 Mon Sep 17 00:00:00 2001
From: Michael Jones <michaelrj at google.com>
Date: Tue, 3 Jun 2025 10:19:52 -0700
Subject: [PATCH 1/2] [libc] Independent strcat/strncat

The previous implementations called other entrypoints. This patch fixes
strcat and strncat to be properly independent.
---
 libc/src/string/CMakeLists.txt |  2 --
 libc/src/string/strcat.cpp     |  9 +++++----
 libc/src/string/strncat.cpp    | 10 +++++-----
 3 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/libc/src/string/CMakeLists.txt b/libc/src/string/CMakeLists.txt
index 2c607bf8ea895..0e9fc33418515 100644
--- a/libc/src/string/CMakeLists.txt
+++ b/libc/src/string/CMakeLists.txt
@@ -110,7 +110,6 @@ add_entrypoint_object(
   HDRS
     strcat.h
   DEPENDS
-    .strcpy
     .string_utils
     libc.include.llvm-libc-types.size_t
 )
@@ -267,7 +266,6 @@ add_entrypoint_object(
   HDRS
     strncat.h
   DEPENDS
-    .strncpy
     .string_utils
     libc.include.llvm-libc-types.size_t
 )
diff --git a/libc/src/string/strcat.cpp b/libc/src/string/strcat.cpp
index 6a6f068bd4759..7dce6d15a65c1 100644
--- a/libc/src/string/strcat.cpp
+++ b/libc/src/string/strcat.cpp
@@ -9,7 +9,6 @@
 #include "src/string/strcat.h"
 #include "src/__support/macros/config.h"
 #include "src/__support/macros/null_check.h"
-#include "src/string/strcpy.h"
 #include "src/string/string_utils.h"
 
 #include "src/__support/common.h"
@@ -21,9 +20,11 @@ LLVM_LIBC_FUNCTION(char *, strcat,
   LIBC_CRASH_ON_NULLPTR(dest);
   LIBC_CRASH_ON_NULLPTR(src);
   size_t dest_length = internal::string_length(dest);
-  size_t src_length = internal::string_length(src);
-  LIBC_NAMESPACE::strcpy(dest + dest_length, src);
-  dest[dest_length + src_length] = '\0';
+  size_t i;
+  for (i = 0; src[i] != '\0'; ++i)
+    dest[dest_length + i] = src[i];
+
+  dest[dest_length + i] = '\0';
   return dest;
 }
 
diff --git a/libc/src/string/strncat.cpp b/libc/src/string/strncat.cpp
index 4926b7d244d12..6d8bb69607486 100644
--- a/libc/src/string/strncat.cpp
+++ b/libc/src/string/strncat.cpp
@@ -10,7 +10,6 @@
 #include "src/__support/macros/config.h"
 #include "src/__support/macros/null_check.h"
 #include "src/string/string_utils.h"
-#include "src/string/strncpy.h"
 
 #include "src/__support/common.h"
 
@@ -23,11 +22,12 @@ LLVM_LIBC_FUNCTION(char *, strncat,
     LIBC_CRASH_ON_NULLPTR(dest);
     LIBC_CRASH_ON_NULLPTR(src);
   }
-  size_t src_length = internal::string_length(src);
-  size_t copy_amount = src_length > count ? count : src_length;
   size_t dest_length = internal::string_length(dest);
-  LIBC_NAMESPACE::strncpy(dest + dest_length, src, copy_amount);
-  dest[dest_length + copy_amount] = '\0';
+  size_t i;
+  for (i = 0; i < count && src[i] != '\0'; ++i)
+    dest[dest_length + i] = src[i];
+
+  dest[dest_length + i] = '\0';
   return dest;
 }
 

>From 565837a814ca40a6b7874d45cd03eda8f995c804 Mon Sep 17 00:00:00 2001
From: Michael Jones <michaelrj at google.com>
Date: Wed, 4 Jun 2025 16:22:07 -0700
Subject: [PATCH 2/2] fix stpcpy as well

---
 libc/src/string/CMakeLists.txt | 1 -
 libc/src/string/stpcpy.cpp     | 6 +++---
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/libc/src/string/CMakeLists.txt b/libc/src/string/CMakeLists.txt
index 0e9fc33418515..0975d8e4177d4 100644
--- a/libc/src/string/CMakeLists.txt
+++ b/libc/src/string/CMakeLists.txt
@@ -89,7 +89,6 @@ add_entrypoint_object(
   HDRS
     stpcpy.h
   DEPENDS
-    .mempcpy
     .string_utils
 )
 
diff --git a/libc/src/string/stpcpy.cpp b/libc/src/string/stpcpy.cpp
index 979edd72c1f1d..fefae81172585 100644
--- a/libc/src/string/stpcpy.cpp
+++ b/libc/src/string/stpcpy.cpp
@@ -8,7 +8,7 @@
 
 #include "src/string/stpcpy.h"
 #include "src/__support/macros/config.h"
-#include "src/string/mempcpy.h"
+#include "src/string/memory_utils/inline_memcpy.h"
 #include "src/string/string_utils.h"
 
 #include "src/__support/common.h"
@@ -18,8 +18,8 @@ namespace LIBC_NAMESPACE_DECL {
 LLVM_LIBC_FUNCTION(char *, stpcpy,
                    (char *__restrict dest, const char *__restrict src)) {
   size_t size = internal::string_length(src) + 1;
-  char *result =
-      reinterpret_cast<char *>(LIBC_NAMESPACE::mempcpy(dest, src, size));
+  inline_memcpy(dest, src, size);
+  char *result = dest + size;
 
   if (result != nullptr)
     return result - 1;