release/20.x: [CSKY] Default to unsigned char

[llvmbot]

Backport d204724

Requested by: @arichardson

[llvmbot]

@zixuan-wu What do you think about merging this PR to the release branch?

[llvmbot]

@llvm/pr-subscribers-clang-driver

@llvm/pr-subscribers-clang

Author: None (llvmbot)

Changes

Backport d204724

Requested by: @arichardson

---

Full diff: https://github.com/llvm/llvm-project/pull/126436.diff

2 Files Affected:

• (modified) clang/lib/Driver/ToolChains/Clang.cpp (+1)
• (modified) clang/test/Driver/csky-toolchain.c (+1)

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 589de953be5be1b..49c6d2b271b3812 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -1358,6 +1358,7 @@ static bool isSignedCharDefault(const llvm::Triple &Triple) {
       return true;
     return false;
 
+  case llvm::Triple::csky:
   case llvm::Triple::hexagon:
   case llvm::Triple::msp430:
   case llvm::Triple::ppcle:
diff --git a/clang/test/Driver/csky-toolchain.c b/clang/test/Driver/csky-toolchain.c
index 66485464652ac87..638ce64ec98cde3 100644
--- a/clang/test/Driver/csky-toolchain.c
+++ b/clang/test/Driver/csky-toolchain.c
@@ -3,6 +3,7 @@
 
 // RUN: %clang -### %s --target=csky 2>&1 | FileCheck -check-prefix=CC1 %s
 // CC1: "-cc1" "-triple" "csky"
+// CC1: "-fno-signed-char"
 
 // In the below tests, --rtlib=platform is used so that the driver ignores
 // the configure-time CLANG_DEFAULT_RTLIB option when choosing the runtime lib

[arichardson]

I feel it would make sense to backport this to the release so that Rust built against LLVM20 has a consistent c_char signedness (rust-lang/rust#132975)

[tstellar]

ping @zixuan-wu

[tstellar]

@AaronBallman In case we don't here from @zixuan-wu in time, as the Lead Mantainer for clang what do you think about backporting this?

[AaronBallman]

LGTM though this definitely needs a release note so that anyone relying on the old behavior has some amount of notice (and a suggestion as to how to get the old behavior back).

[tstellar]

@arichardson Would you be able to create a follow-up PR with the a release note entry?

[arichardson]

@arichardson Would you be able to create a follow-up PR with the a release note entry?

Sure, will do this.

[github-actions]

@arichardson (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR.

[arichardson]

@arichardson (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR.

Prior to Clang 20, the CSKY target used an incorrect ABI with char being signed instead of unsigned. Code that relies on the incorrect definition can restore the old behavior by passing -fsigned-char.