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

[Michael Jones via libc-commits]

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

The previous implementations called other entrypoints. This patch fixes
strcat and strncat to be properly independent.


>From 07a06481b161953932bdf8ea2df9ae15956182cc 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] [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    | 9 +++++----
 3 files changed, 10 insertions(+), 10 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 0eb189ce204f0..4b6717c3c98e5 100644
--- a/libc/src/string/strcat.cpp
+++ b/libc/src/string/strcat.cpp
@@ -8,7 +8,6 @@
 
 #include "src/string/strcat.h"
 #include "src/__support/macros/config.h"
-#include "src/string/strcpy.h"
 #include "src/string/string_utils.h"
 
 #include "src/__support/common.h"
@@ -18,9 +17,11 @@ namespace LIBC_NAMESPACE_DECL {
 LLVM_LIBC_FUNCTION(char *, strcat,
                    (char *__restrict dest, const char *__restrict 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 221881f93c47a..abd8d001f779c 100644
--- a/libc/src/string/strncat.cpp
+++ b/libc/src/string/strncat.cpp
@@ -18,11 +18,12 @@ namespace LIBC_NAMESPACE_DECL {
 LLVM_LIBC_FUNCTION(char *, strncat,
                    (char *__restrict dest, const char *__restrict src,
                     size_t count)) {
-  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;
 }