[libc-commits] [libc] [libc] Add __iso99_fscanf alias. (PR #213125)

[via libc-commits]

https://github.com/lntue updated https://github.com/llvm/llvm-project/pull/213125

>From 1370b6876395ff3876fd4391280e593a5c2d77ff Mon Sep 17 00:00:00 2001
From: Tue Ly <lntue.h at gmail.com>
Date: Thu, 30 Jul 2026 19:59:22 +0000
Subject: [PATCH 1/2] [libc] Add __iso99_fscanf alias.

---
 libc/src/__support/common.h         | 17 +++++++++++++++++
 libc/src/stdio/baremetal/fscanf.cpp |  5 +++++
 2 files changed, 22 insertions(+)

diff --git a/libc/src/__support/common.h b/libc/src/__support/common.h
index d90fe7b8ae98d..e946ee4e0fb20 100644
--- a/libc/src/__support/common.h
+++ b/libc/src/__support/common.h
@@ -56,17 +56,34 @@
       __##name##_impl__ asm(c_alias);                                          \
   decltype(LIBC_NAMESPACE::name) name [[gnu::alias(c_alias)]];                 \
   type __##name##_impl__ arglist
+
+#define LLVM_LIBC_ADD_FUNCTION_C_ALIAS(name, c_alias)                          \
+  extern "C" decltype(LIBC_NAMESPACE::name) c_alias [[gnu::alias(#name)]];     \
+  static_assert(true, "Require semicolon.")
+
 #else // __APPLE__
 #define LLVM_LIBC_FUNCTION_IMPL_4(type, name, arglist, c_alias)                \
   LLVM_LIBC_ATTR(name)                                                         \
   LLVM_LIBC_FUNCTION_ATTR decltype(LIBC_NAMESPACE::name) name asm(             \
       "_" c_alias);                                                            \
   type name arglist
+
+// clang-format off
+#define LLVM_LIBC_ADD_FUNCTION_C_ALIAS(name, c_alias)                          \
+  asm(".text\n"                                                                \
+      ".global " "_" #c_alias "\n"                                             \
+      ".type " "_" #c_alias ", @function\n"                                    \
+      "_" #c_alias " = " "_" #name "\n");                                      \
+  static_assert(true, "Require semicolon.")
+// clang-format on
 #endif // __APPLE__
 
 #else  // LIBC_COPT_PUBLIC_PACKAGING
 #define LLVM_LIBC_FUNCTION_IMPL_4(type, name, arglist, c_alias)                \
   type name arglist
+
+#define LLVM_LIBC_ADD_FUNCTION_C_ALIAS(name, c_alias)
+
 #endif // LIBC_COPT_PUBLIC_PACKAGING
 
 #define LLVM_LIBC_FUNCTION_IMPL_3(type, name, arglist)                         \
diff --git a/libc/src/stdio/baremetal/fscanf.cpp b/libc/src/stdio/baremetal/fscanf.cpp
index eb8b2326ad6b7..d20dd51cce657 100644
--- a/libc/src/stdio/baremetal/fscanf.cpp
+++ b/libc/src/stdio/baremetal/fscanf.cpp
@@ -36,3 +36,8 @@ LLVM_LIBC_FUNCTION(int, fscanf,
 }
 
 } // namespace LIBC_NAMESPACE_DECL
+
+#if ...
+// comments...
+LLVM_LIBC_ADD_FUNCTION_C_ALIAS(fscanf, __isoc99_fscanf);
+#endif

>From 7f08fc197cdad2dd50721f9309f524c17d93c9ce Mon Sep 17 00:00:00 2001
From: Tue Ly <lntue.h at gmail.com>
Date: Fri, 31 Jul 2026 14:58:58 +0000
Subject: [PATCH 2/2] Specify guard.

---
 libc/src/stdio/baremetal/fscanf.cpp | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/libc/src/stdio/baremetal/fscanf.cpp b/libc/src/stdio/baremetal/fscanf.cpp
index d20dd51cce657..36ecd27ea0e98 100644
--- a/libc/src/stdio/baremetal/fscanf.cpp
+++ b/libc/src/stdio/baremetal/fscanf.cpp
@@ -37,7 +37,6 @@ LLVM_LIBC_FUNCTION(int, fscanf,
 
 } // namespace LIBC_NAMESPACE_DECL
 
-#if ...
-// comments...
+#ifdef LIBC_STDIO_ADD_ISO99_FSCANF
 LLVM_LIBC_ADD_FUNCTION_C_ALIAS(fscanf, __isoc99_fscanf);
-#endif
+#endif // LIBC_STDIO_ADD_ISO99_FSCANF