[libc] Add vsscanf function

[izaakschroeder]

Still needs proper implementation, but stubs are here.

See:

• https://linux.die.net/man/3/vsscanf
• https://android.googlesource.com/platform/bionic/+/froyo-release/libc/stdio/vsscanf.c

[llvmbot]

@llvm/pr-subscribers-libc

Author: Izaak Schroeder (izaakschroeder)

Changes

Still needs proper implementation, but stubs are here.

---

Full diff: https://github.com/llvm/llvm-project/pull/97529.diff

4 Files Affected:

• (modified) libc/spec/stdc.td (+7)
• (modified) libc/src/stdio/CMakeLists.txt (+10)
• (added) libc/src/stdio/vsscanf.cpp (+28)
• (added) libc/src/stdio/vsscanf.h (+21)

diff --git a/libc/spec/stdc.td b/libc/spec/stdc.td
index 9ff40bf76700c..0d35a1e3e6203 100644
--- a/libc/spec/stdc.td
+++ b/libc/spec/stdc.td
@@ -968,6 +968,13 @@ def StdC : StandardSpec<"stdc"> {
               RetValSpec<IntType>,
               [ArgSpec<IntType>, ArgSpec<FILEPtr>]
           >,
+          FunctionSpec<
+              "vsscanf",
+              RetValSpec<IntType>,
+              [ArgSpec<ConstCharPtr>,
+               ArgSpec<ConstCharPtr>,
+               ArgSpec<VaListType>]
+          >,
       ],
       [
           ObjectSpec<
diff --git a/libc/src/stdio/CMakeLists.txt b/libc/src/stdio/CMakeLists.txt
index a659d9e847a9e..3f1d97cad6afd 100644
--- a/libc/src/stdio/CMakeLists.txt
+++ b/libc/src/stdio/CMakeLists.txt
@@ -203,6 +203,16 @@ add_entrypoint_object(
     libc.src.stdio.printf_core.vfprintf_internal
 )
 
+add_entrypoint_object(
+  vsscanf
+  SRCS
+    vsscanf.cpp
+  HDRS
+    vsscanf.h
+  DEPENDS
+    libc.src.__support.arg_list
+)
+
 add_stdio_entrypoint_object(
   fileno
   SRCS
diff --git a/libc/src/stdio/vsscanf.cpp b/libc/src/stdio/vsscanf.cpp
new file mode 100644
index 0000000000000..b5c9173387ea0
--- /dev/null
+++ b/libc/src/stdio/vsscanf.cpp
@@ -0,0 +1,28 @@
+//===-- Implementation of vsscanf -------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdio/vsscanf.h"
+
+#include "src/__support/arg_list.h"
+
+#include <stdarg.h>
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(int, vsscanf,
+                   (const char *, const char *,
+                    va_list vlist)) {
+  internal::ArgList args(vlist); // This holder class allows for easier copying
+                                 // and pointer semantics, as well as handling
+                                 // destruction automatically.
+
+  
+  return -1;
+}
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdio/vsscanf.h b/libc/src/stdio/vsscanf.h
new file mode 100644
index 0000000000000..5f32f7ed351b1
--- /dev/null
+++ b/libc/src/stdio/vsscanf.h
@@ -0,0 +1,21 @@
+//===-- Implementation header of vsscanf ------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDIO_VSSCANF_H
+#define LLVM_LIBC_SRC_STDIO_VSSCANF_H
+
+#include <stdarg.h>
+
+namespace LIBC_NAMESPACE {
+
+int vsscanf(const char * s, const char * format,
+             va_list vlist);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDIO_VSSCANF_H

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[jhuber6]

The implementation is trivial here, can you go ahead and do it? All you need to do is copy the code from sscanf sans the va_list creation.

[izaakschroeder]

@jhuber6 did my best! 😅

[jhuber6]

Thanks, now we just need a test. I think you should add this to every config/*/entrypoints.txt that already contains sscanf. The test should then add vsscanf as a dependency in the CMakeLists.txt. Add a single test that calls vsscanf using an existing va_list.

[michaelrj-google]

you should also add vsscanf to entrypoints.txt for the relevant platforms

[jhuber6]

Looks fine as is, but I'd change the invocations like

auto fn = [](const char *str, const char *fmt, ...) -> int { ... };
fn("Not an Integer", %d, &result);

[jhuber6]

Can you make the above suggestions and add this to the entrypoints.txt for every target that already contains sscanf?

[jhuber6]

merged in #101402, thanks for the initial patch.