[libcxx-commits] [libcxx] [ASan][libc++] Correct (explicit) annotation size (PR #79292)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Tacet (AdvenamTacet)

<details>
<summary>Changes</summary>

A quick examination suggests that the current code in the codebase does not lead to incorrect annotations. However, the intention is for the object after the function to be annotated in a way that only its contents are unpoisoned and the rest is poisoned. This commit makes it explicit and avoids potential issues in future.

In addition, I have implemented a few tests for a function that helped me identify the specific argument value.

---
Full diff: https://github.com/llvm/llvm-project/pull/79292.diff


2 Files Affected:

- (modified) libcxx/include/string (+1-1) 
- (modified) libcxx/test/std/strings/basic.string/string.modifiers/string_append/pointer_size.pass.cpp (+6) 


``````````diff
diff --git a/libcxx/include/string b/libcxx/include/string
index e97139206d4fa7c..e69da6e61d11b27 100644
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -2385,7 +2385,7 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 void basic_string<_CharT, _Traits, _Allocator>::__
   __old_sz = __n_copy + __n_add + __sec_cp_sz;
   __set_long_size(__old_sz);
   traits_type::assign(__p[__old_sz], value_type());
-  __annotate_new(__old_cap + __delta_cap);
+  __annotate_new(__old_sz);
 }
 
 // __grow_by is deprecated because it does not set the size. It may not update the size when the size is changed, and it
diff --git a/libcxx/test/std/strings/basic.string/string.modifiers/string_append/pointer_size.pass.cpp b/libcxx/test/std/strings/basic.string/string.modifiers/string_append/pointer_size.pass.cpp
index 93e7500a11967ce..6eac4082fba0216 100644
--- a/libcxx/test/std/strings/basic.string/string.modifiers/string_append/pointer_size.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.modifiers/string_append/pointer_size.pass.cpp
@@ -36,6 +36,7 @@ TEST_CONSTEXPR_CXX20 void test_string() {
   test(S(), "12345678901234567890", 1, S("1"));
   test(S(), "12345678901234567890", 3, S("123"));
   test(S(), "12345678901234567890", 20, S("12345678901234567890"));
+  test(S(), "1234567890123456789012345678901234567890", 40, S("1234567890123456789012345678901234567890"));
 
   test(S("12345"), "", 0, S("12345"));
   test(S("12345"), "12345", 5, S("1234512345"));
@@ -44,6 +45,11 @@ TEST_CONSTEXPR_CXX20 void test_string() {
   test(S("12345678901234567890"), "", 0, S("12345678901234567890"));
   test(S("12345678901234567890"), "12345", 5, S("1234567890123456789012345"));
   test(S("12345678901234567890"), "12345678901234567890", 20, S("1234567890123456789012345678901234567890"));
+
+  // Starting from long string (no SSO)
+  test(S("1234567890123456789012345678901234567890"), "", 0, S("1234567890123456789012345678901234567890"));
+  test(S("1234567890123456789012345678901234567890"), "a", 1, S("1234567890123456789012345678901234567890a"));
+  test(S("1234567890123456789012345678901234567890"), "aaaaaaaaaa", 10, S("1234567890123456789012345678901234567890aaaaaaaaaa"));
 }
 
 TEST_CONSTEXPR_CXX20 bool test() {

``````````

</details>


https://github.com/llvm/llvm-project/pull/79292