[libc-commits] [libc] 3dc1b50 - [libc] Make 'printf' converter output "(null)" instead of "null" (#85845)

[via libc-commits]

Author: Joseph Huber
Date: 2024-03-19T14:44:59-05:00
New Revision: 3dc1b5044e25fc7e574719355091fccddad29ce4

URL: https://github.com/llvm/llvm-project/commit/3dc1b5044e25fc7e574719355091fccddad29ce4
DIFF: https://github.com/llvm/llvm-project/commit/3dc1b5044e25fc7e574719355091fccddad29ce4.diff

LOG: [libc] Make 'printf' converter output "(null)" instead of "null" (#85845)

Summary:
Currently we print `null` for the null pointer in a `%s` expression.
Although it's not defined by the standard, other implementations choose
to use `(null)` to indicate this. We also currently print `(nullptr)` so
I think it's more consistent to use parens in both cases.

Added: 
    

Modified: 
    libc/docs/dev/printf_behavior.rst
    libc/docs/dev/undefined_behavior.rst
    libc/src/stdio/printf_core/string_converter.h
    libc/test/src/stdio/sprintf_test.cpp

Removed: 
    


################################################################################
diff  --git a/libc/docs/dev/printf_behavior.rst b/libc/docs/dev/printf_behavior.rst
index 00d6c83f4b0d36..9548bfda57aa7d 100644
--- a/libc/docs/dev/printf_behavior.rst
+++ b/libc/docs/dev/printf_behavior.rst
@@ -1,3 +1,5 @@
+.. _printf_behavior:
+
 ====================================
 Printf Behavior Under All Conditions
 ====================================

diff  --git a/libc/docs/dev/undefined_behavior.rst b/libc/docs/dev/undefined_behavior.rst
index 3a06b7007febd4..50e8bdde89ddd6 100644
--- a/libc/docs/dev/undefined_behavior.rst
+++ b/libc/docs/dev/undefined_behavior.rst
@@ -74,3 +74,10 @@ The POSIX.1 standard does not delineate the behavior consequent to invoking hsea
 Path without Leading Slashs in shm_open
 ----------------------------------------
 POSIX.1 leaves that when the name of a shared memory object does not begin with a slash, the behavior is implementation defined. In such cases, the shm_open in LLVM libc is implemented to behave as if the name began with a slash.
+
+Handling of NULL arguments to the 's' format specifier
+------------------------------------------------------
+The C standard does not specify behavior for ``printf("%s", NULL)``. We will
+print the string literal ``(null)`` unless using the 
+``LIBC_COPT_PRINTF_NO_NULLPTR_CHECKS`` option described in :ref:`printf 
+behavior<printf_behavior>`.

diff  --git a/libc/src/stdio/printf_core/string_converter.h b/libc/src/stdio/printf_core/string_converter.h
index 04dc5a06da2226..9e05591079faa4 100644
--- a/libc/src/stdio/printf_core/string_converter.h
+++ b/libc/src/stdio/printf_core/string_converter.h
@@ -25,7 +25,7 @@ LIBC_INLINE int convert_string(Writer *writer, const FormatSection &to_conv) {
 
 #ifndef LIBC_COPT_PRINTF_NO_NULLPTR_CHECKS
   if (str_ptr == nullptr) {
-    str_ptr = "null";
+    str_ptr = "(null)";
   }
 #endif // LIBC_COPT_PRINTF_NO_NULLPTR_CHECKS
 

diff  --git a/libc/test/src/stdio/sprintf_test.cpp b/libc/test/src/stdio/sprintf_test.cpp
index ab8bdb23b1187c..8dde95d02a96dc 100644
--- a/libc/test/src/stdio/sprintf_test.cpp
+++ b/libc/test/src/stdio/sprintf_test.cpp
@@ -121,8 +121,8 @@ TEST(LlvmLibcSPrintfTest, StringConv) {
 
 #ifndef LIBC_COPT_PRINTF_NO_NULLPTR_CHECKS
   written = LIBC_NAMESPACE::sprintf(buff, "%s", nullptr);
-  EXPECT_EQ(written, 4);
-  ASSERT_STREQ(buff, "null");
+  EXPECT_EQ(written, 6);
+  ASSERT_STREQ(buff, "(null)");
 #endif // LIBC_COPT_PRINTF_NO_NULLPTR_CHECKS
 }