[clang] [Clang][Hexagon] Define _GNU_SOURCE when using picolibc in C++ mode (PR #201599)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: quic-k

<details>
<summary>Changes</summary>

picolibc guards GNU-extension locale functions (e.g. strtold_l) behind __GNU_VISIBLE, which is only enabled when _GNU_SOURCE is defined. Without it, building libcxx against picolibc fails because these functions are undeclared.

Add _GNU_SOURCE automatically in HexagonToolChain::addClangTargetOptions when --cstdlib=picolibc is used and the driver is in C++ mode (CCCIsCXX)

---
Full diff: https://github.com/llvm/llvm-project/pull/201599.diff


2 Files Affected:

- (modified) clang/lib/Driver/ToolChains/Hexagon.cpp (+7) 
- (modified) clang/test/Driver/hexagon-toolchain-picolibc.c (+12) 


``````````diff
diff --git a/clang/lib/Driver/ToolChains/Hexagon.cpp b/clang/lib/Driver/ToolChains/Hexagon.cpp
index ce3fd5110953a..b28da09d83a75 100644
--- a/clang/lib/Driver/ToolChains/Hexagon.cpp
+++ b/clang/lib/Driver/ToolChains/Hexagon.cpp
@@ -815,6 +815,13 @@ void HexagonToolChain::addClangTargetOptions(const ArgList &DriverArgs,
     CC1Args.push_back("-mllvm");
     CC1Args.push_back("-hexagon-autohvx");
   }
+
+  // picolibc guards GNU-extension functions (e.g. strtold_l) with __GNU_VISIBLE
+  // which requires _GNU_SOURCE. Define it automatically for C++ compilations
+  // so that building libcxx against picolibc works without -D_GNU_SOURCE.
+  if (GetCStdlibType(DriverArgs) == ToolChain::CST_Picolibc &&
+      getDriver().CCCIsCXX())
+    CC1Args.push_back("-D_GNU_SOURCE");
 }
 
 void HexagonToolChain::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
diff --git a/clang/test/Driver/hexagon-toolchain-picolibc.c b/clang/test/Driver/hexagon-toolchain-picolibc.c
index 8282a4da81636..4087d66e08f17 100644
--- a/clang/test/Driver/hexagon-toolchain-picolibc.c
+++ b/clang/test/Driver/hexagon-toolchain-picolibc.c
@@ -236,3 +236,15 @@
 // RUN:   -mcpu=hexagonv68 -G0 -### %s 2>&1 | FileCheck -check-prefix=CHECK-H2-LIBPATHS-G0 %s
 // CHECK-H2-LIBPATHS-G0: "-L{{.*}}{{/|\\\\}}Inputs{{/|\\\\}}hexagon_tree{{/|\\\\}}Tools{{/|\\\\}}bin{{/|\\\\}}..{{/|\\\\}}target{{/|\\\\}}picolibc{{/|\\\\}}hexagon-unknown-h2-elf{{/|\\\\}}lib{{/|\\\\}}v68{{/|\\\\}}G0"
 // CHECK-H2-LIBPATHS-G0: "-L{{.*}}{{/|\\\\}}Inputs{{/|\\\\}}hexagon_tree{{/|\\\\}}Tools{{/|\\\\}}bin{{/|\\\\}}..{{/|\\\\}}target{{/|\\\\}}picolibc{{/|\\\\}}hexagon-unknown-h2-elf{{/|\\\\}}lib{{/|\\\\}}v68"
+
+// -----------------------------------------------------------------------------
+// picolibc: _GNU_SOURCE is defined automatically for C++ (needed for strtold_l etc.)
+// -----------------------------------------------------------------------------
+// RUN: %clangxx --target=hexagon-h2-elf --cstdlib=picolibc -### %s 2>&1 | FileCheck %s --check-prefix=CHECK-GNU-SOURCE
+// CHECK-GNU-SOURCE: "-D_GNU_SOURCE"
+//
+// RUN: %clang --target=hexagon-h2-elf --cstdlib=picolibc -### %s 2>&1 | FileCheck %s --check-prefix=CHECK-C-NO-GNU-SOURCE
+// CHECK-C-NO-GNU-SOURCE-NOT: "-D_GNU_SOURCE"
+//
+// RUN: %clang --target=hexagon-h2-elf -### %s 2>&1 | FileCheck %s --check-prefix=CHECK-NO-PICOLIBC
+// CHECK-NO-PICOLIBC-NOT: "-D_GNU_SOURCE"

``````````

</details>


https://github.com/llvm/llvm-project/pull/201599