[libc] Remove hardcoded sizeof in __barrier_type.h

[mikhailramalho]

This PR modifies the static_asserts checking the expected sizes in __barrier_type.h, so that we can guarantee that our internal implementation fits the public header.

[llvmbot]

@llvm/pr-subscribers-libc

Author: Mikhail R. Gadelha (mikhailramalho)

Changes

This PR removes the hardcoded values for the sizeof(LIBC_NAMESPACE::CndVar) and sizeof(LIBC_NAMESPACE::Mutex) and replaces them with the actual calls to sizeof. Fixes compilation error in 32-bit systems.

---

Full diff: https://github.com/llvm/llvm-project/pull/153718.diff

1 Files Affected:

• (modified) libc/include/llvm-libc-types/__barrier_type.h (+6-3)

diff --git a/libc/include/llvm-libc-types/__barrier_type.h b/libc/include/llvm-libc-types/__barrier_type.h
index 59712619e917d..23593372af56e 100644
--- a/libc/include/llvm-libc-types/__barrier_type.h
+++ b/libc/include/llvm-libc-types/__barrier_type.h
@@ -9,13 +9,16 @@
 #ifndef LLVM_LIBC_TYPES__BARRIER_TYPE_H
 #define LLVM_LIBC_TYPES__BARRIER_TYPE_H
 
+#include "src/__support/threads/CndVar.h"
+#include "src/__support/threads/mutex.h"
+
 typedef struct __attribute__((aligned(8 /* alignof (Barrier) */))) {
   unsigned expected;
   unsigned waiting;
   bool blocking;
-  char entering[24 /* sizeof (CndVar) */];
-  char exiting[24 /* sizeof (CndVar) */];
-  char mutex[24 /* sizeof (Mutex) */];
+  char entering[sizeof(LIBC_NAMESPACE::CndVar)];
+  char exiting[sizeof(LIBC_NAMESPACE::CndVar)];
+  char mutex[sizeof(LIBC_NAMESPACE::Mutex)];
 } __barrier_type;
 
 #endif // LLVM_LIBC_TYPES__BARRIER_TYPE_H

[frobtech]

Sorry, this is a non-starter. The public header files in include/ cannot refer to anything outside include/. The whole point of these is to define the public ABI. The approach you'll need to take instead is to have the implementation code static_assert that the sizes and alignments maintained in the public header are always sufficient. If those assertions ever fail, it will have to be an explicit ABI-breaking manual change to update the public ABI.

[SchrodingerZhu]

Yeah, more importantly, the headers are intended for C language. C++ namespace cannot work here.

[SchrodingerZhu]

I am leaning to use __mutex_type

[mikhailramalho]

Got it, I'll try to find another solution.

[mikhailramalho]

Folks, I've changed the static_assert to check if the sizes are smaller than the ones defined in the public headers. WDYT?

I'll update the PR title before we land it, if this is accepted. The PR summary was updated.

[mikhailramalho]

ping