[clang] Fix catching pointers by reference on mingw targets #162546
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For this specific case, when catching a pointer data type, by reference, Clang generates a special code pattern, which directly accesses the exception data by skipping past the `_Unwind_Exception` manually (rather than using the return value of `__cxa_begin_catch`). On most platforms, `_Unwind_Exception` is 32 bytes, but in some configurations it's different. (ARM EHABI is one preexisting case.) In the case of SEH, it's also different - it is 48 bytes in 32 bit mode and 64 bytes in 64 bit mode. Handle this case in `TargetCodeGenInfo::getSizeOfUnwindException`, fixing the code generation for catching pointers by reference. This fixes mstorsjo/llvm-mingw#522.
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@llvm/pr-subscribers-clang @llvm/pr-subscribers-clang-codegen Author: Martin Storsjö (mstorsjo) ChangesFor this specific case, when catching a pointer data type, by reference, Clang generates a special code pattern, which directly accesses the exception data by skipping past the On most platforms, Handle this case in This fixes mstorsjo/llvm-mingw#522. Full diff: https://github.com/llvm/llvm-project/pull/162546.diff 2 Files Affected:
diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index 1e58c3f217812..342a3af0ac1ee 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -82,6 +82,8 @@ TargetCodeGenInfo::~TargetCodeGenInfo() = default;
// If someone can figure out a general rule for this, that would be great.
// It's probably just doomed to be platform-dependent, though.
unsigned TargetCodeGenInfo::getSizeOfUnwindException() const {
+ if (getABIInfo().getCodeGenOpts().hasSEHExceptions())
+ return getABIInfo().getDataLayout().getPointerSizeInBits() > 32 ? 64 : 48;
// Verified for:
// x86-64 FreeBSD, Linux, Darwin
// x86-32 FreeBSD, Linux, Darwin
diff --git a/clang/test/CodeGenCXX/sizeof-unwind-exception.cpp b/clang/test/CodeGenCXX/sizeof-unwind-exception.cpp
index 4fb977a5367e7..e40b2d7ae43ea 100644
--- a/clang/test/CodeGenCXX/sizeof-unwind-exception.cpp
+++ b/clang/test/CodeGenCXX/sizeof-unwind-exception.cpp
@@ -3,6 +3,8 @@
// RUN: %clang_cc1 -triple x86_64-apple-darwin10 -emit-llvm -fcxx-exceptions -fexceptions %s -O2 -o - | FileCheck %s --check-prefix=ARM-DARWIN
// RUN: %clang_cc1 -triple arm-unknown-gnueabi -emit-llvm -fcxx-exceptions -fexceptions %s -O2 -o - | FileCheck %s --check-prefix=ARM-EABI
// RUN: %clang_cc1 -triple mipsel-unknown-unknown -emit-llvm -fcxx-exceptions -fexceptions %s -O2 -o - | FileCheck %s --check-prefix=MIPS
+// RUN: %clang_cc1 -triple x86_64-windows-gnu -emit-llvm -fcxx-exceptions -fexceptions -exception-model=seh %s -O2 -o - | FileCheck %s --check-prefix=MINGW-X86-64
+// RUN: %clang_cc1 -triple thumbv7-windows-gnu -emit-llvm -fcxx-exceptions -fexceptions -exception-model=seh %s -O2 -o - | FileCheck %s --check-prefix=MINGW-ARMV7
void foo();
void test() {
@@ -25,9 +27,15 @@ void test() {
// ARM-EABI-NEXT: [[T1:%.*]] = getelementptr i8, ptr [[EXN]], i32 88
// MIPS: [[T0:%.*]] = tail call ptr @__cxa_begin_catch(ptr [[EXN:%.*]]) [[NUW:#[0-9]+]]
// MIPS-NEXT: [[T1:%.*]] = getelementptr i8, ptr [[EXN]], i32 24
+// MINGW-X86-64: [[T0:%.*]] = tail call ptr @__cxa_begin_catch(ptr [[EXN:%.*]]) [[NUW:#[0-9]+]]
+// MINGW-X86-64-NEXT:[[T1:%.*]] = getelementptr i8, ptr [[EXN]], i64 64
+// MINGW-ARMV7: [[T0:%.*]] = tail call arm_aapcs_vfpcc ptr @__cxa_begin_catch(ptr [[EXN:%.*]]) [[NUW:#[0-9]+]]
+// MINGW-ARMV7-NEXT: [[T1:%.*]] = getelementptr i8, ptr [[EXN]], i32 48
// X86-64: attributes [[NUW]] = { nounwind }
// X86-32: attributes [[NUW]] = { nounwind }
// ARM-DARWIN: attributes [[NUW]] = { nounwind }
// ARM-EABI: attributes [[NUW]] = { nounwind }
// MIPS: attributes [[NUW]] = { nounwind }
+// MINGW-X86-64: attributes [[NUW]] = { nounwind }
+// MINGW-ARMV7: attributes [[NUW]] = { nounwind }
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The header also checks that |
Possibly, yes. I think those ifdefs stem from the corresponding cases in GCC's |
Not sure if there's much extra explanation needed here; |
cjacek
approved these changes
Oct 13, 2025
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If others don't mind, I'll go ahead and merge this one soon. |
efriedma-quic
approved these changes
Oct 15, 2025
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/cherry-pick 10be254 |
|
/pull-request #163714 |
|
LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/65/builds/24069 Here is the relevant piece of the build log for the reference |
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) For this specific case, when catching a pointer data type, by reference, Clang generates a special code pattern, which directly accesses the exception data by skipping past the `_Unwind_Exception` manually (rather than using the return value of `__cxa_begin_catch`). On most platforms, `_Unwind_Exception` is 32 bytes, but in some configurations it's different. (ARM EHABI is one preexisting case.) In the case of SEH, it's also different - it is 48 bytes in 32 bit mode and 64 bytes in 64 bit mode. (See the SEH ifdef in `_Unwind_Exception` in `clang/lib/Headers/unwind.h`.) Handle this case in `TargetCodeGenInfo::getSizeOfUnwindException`, fixing the code generation for catching pointers by reference. This fixes mstorsjo/llvm-mingw#522. (cherry picked from commit 10be254)
c-rhodes
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Oct 17, 2025
) For this specific case, when catching a pointer data type, by reference, Clang generates a special code pattern, which directly accesses the exception data by skipping past the `_Unwind_Exception` manually (rather than using the return value of `__cxa_begin_catch`). On most platforms, `_Unwind_Exception` is 32 bytes, but in some configurations it's different. (ARM EHABI is one preexisting case.) In the case of SEH, it's also different - it is 48 bytes in 32 bit mode and 64 bytes in 64 bit mode. (See the SEH ifdef in `_Unwind_Exception` in `clang/lib/Headers/unwind.h`.) Handle this case in `TargetCodeGenInfo::getSizeOfUnwindException`, fixing the code generation for catching pointers by reference. This fixes mstorsjo/llvm-mingw#522. (cherry picked from commit 10be254)
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For this specific case, when catching a pointer data type, by reference, Clang generates a special code pattern, which directly accesses the exception data by skipping past the
_Unwind_Exceptionmanually (rather than using the return value of__cxa_begin_catch).On most platforms,
_Unwind_Exceptionis 32 bytes, but in some configurations it's different. (ARM EHABI is one preexisting case.) In the case of SEH, it's also different - it is 48 bytes in 32 bit mode and 64 bytes in 64 bit mode. (See the SEH ifdef in_Unwind_Exceptioninclang/lib/Headers/unwind.h.)Handle this case in
TargetCodeGenInfo::getSizeOfUnwindException, fixing the code generation for catching pointers by reference.This fixes mstorsjo/llvm-mingw#522.