Benoit Belley
2014-Dec-10 17:15 UTC
[LLVMdev] [PATCH] MCJIT/ELF should support MSVC C++ mangled symbols
Hi everyone,
We have found a problem while using the MCJIT engine on Windows. Our jitted code
is invoking some external C++ functions. These external functions have names
that are mangled using the MSVC C++ naming convention. These were not handled
properly by the ELObjectWriter.
The attached patch addresses this issue. The patch is against the LLVM
release_35 branch (Revision 223459). The patch also includes a regression test.
We have successfully ran all LLVM & Clang regression tests after applying
the patch on both Debug+Assert and Release builds.
Regards,
Benoit
------
The ELF format is used on Windows by the MCJIT engine.
Thus, on Windows, the ELFObjectWriter can encounter symbols mangled
using the MS Visual Studio C++ name mangling. Symbols mangled using the
MSVC C++ name mangling can legally have "@@@" as a substring. The
EFLObjectWriter should not interpret the "@@@" substring as specifying
GNU-style symbol versioning. The ELFObjectWriter therefore check for
the MSVC C++ name mangling prefix which is either "?", "@?",
"__imp_?"
or "__imp_?@".
---
lib/MC/ELFObjectWriter.cpp | 38 +++++++++++++++++++++++------
test/MC/ELF/symver-msvc.s | 60 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 91 insertions(+), 7 deletions(-)
create mode 100644 test/MC/ELF/symver-msvc.s
diff --git a/lib/MC/ELFObjectWriter.cpp b/lib/MC/ELFObjectWriter.cpp
index 5779b27..9fddca5 100644
--- a/lib/MC/ELFObjectWriter.cpp
+++ b/lib/MC/ELFObjectWriter.cpp
@@ -1051,14 +1051,38 @@ ELFObjectWriter::computeSymbolTable(MCAssembler
&Asm, const MCAsmLayout &Layout,
// The @@@ in symbol version is replaced with @ in undefined symbols and
// @@ in defined ones.
+ //
+ // We have to be careful though:
+ //
+ // The ELF format is used on Windows by the MCJIT engine. Thus, on
+ // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
+ // Visual Studio C++ name mangling. Symbols mangled using the MSVC C++
+ // name mangling can legally have "@@@" as a sub-string. The
+ // EFLObjectWriter should not interpret the "@@@" sub-string as
specifying
+ // GNU-style symbol versioning. The ELFObjectWriter therefore check for
+ // the MSVC C++ name mangling prefix which is either "?",
"@?", "__imp_?"
+ // or "__imp_@?".
+ //
+ // It would have been interesting to be able to perform this ms mangling
+ // prefix check only when the target triple is of the form *-pc-windows-elf
+ // but it seems that this information is not easily accessible from the
+ // ELFObjectWriter.
StringRef Name = Symbol.getName();
- SmallString<32> Buf;
- size_t Pos = Name.find("@@@");
- if (Pos != StringRef::npos) {
- Buf += Name.substr(0, Pos);
- unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
- Buf += Name.substr(Pos + Skip);
- Name = Buf;
+ if ( !Name.startswith("?")
+ && !Name.startswith("@?")
+ && !Name.startswith("__imp_?")
+ && !Name.startswith("__imp_@?")) {
+ // This symbol isn't following the MSVC C++ name mangling convention.
We
+ // can thus safely interpret the @@@ in symbol names as specifying
+ // symbol versioning.
+ SmallString<32> Buf;
+ size_t Pos = Name.find("@@@");
+ if (Pos != StringRef::npos) {
+ Buf += Name.substr(0, Pos);
+ unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
+ Buf += Name.substr(Pos + Skip);
+ Name = Buf;
+ }
}
MSD.Name = StrTabBuilder.add(Name);
diff --git a/test/MC/ELF/symver-msvc.s b/test/MC/ELF/symver-msvc.s
new file mode 100644
index 0000000..4a40791
--- /dev/null
+++ b/test/MC/ELF/symver-msvc.s
@@ -0,0 +1,60 @@
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-windows-elf %s -o - |
llvm-readobj -r -t | FileCheck %s
+
+// Verify that MSVC C++ mangled symbol are not affected by the
+// ELF symbol versioning. The ELF format is used on Windows by the
+// MCJIT execution engine.
+
+
+ .long "??_R0?AVexception at std@@@8"
+ .long "@??_R0?AVinvalid_argument at std@@@8"
+ .long "__imp_??_R0?AVlogic_error at std@@@8"
+ .long "__imp_@??_R0PAVexception at std@@@8"
+
+
+// CHECK: Relocations [
+// CHECK-NEXT: Section (2) .rela.text {
+// CHECK-NEXT: 0x0 R_X86_64_32 ??_R0?AVexception at std@@@8 0x0
+// CHECK-NEXT: 0x4 R_X86_64_32 @??_R0?AVinvalid_argument at std@@@8 0x0
+// CHECK-NEXT: 0x8 R_X86_64_32 __imp_??_R0?AVlogic_error at std@@@8 0x0
+// CHECK-NEXT: 0xC R_X86_64_32 __imp_@??_R0PAVexception at std@@@8 0x0
+// CHECK-NEXT: }
+// CHECK-NEXT: ]
+
+// CHECK: Symbols [
+// CHECK: Symbol {
+// CHECK: Name: ??_R0?AVexception at std@@@8 (102)
+// CHECK-NEXT: Value: 0x0
+// CHECK-NEXT: Size: 0
+// CHECK-NEXT: Binding: Global (0x1)
+// CHECK-NEXT: Type: None (0x0)
+// CHECK-NEXT: Other: 0
+// CHECK-NEXT: Section: Undefined (0x0)
+// CHECK-NEXT: }
+// CHECK-NEXT: Symbol {
+// CHECK-NEXT: Name: @??_R0?AVinvalid_argument at std@@@8 (1)
+// CHECK-NEXT: Value: 0x0
+// CHECK-NEXT: Size: 0
+// CHECK-NEXT: Binding: Global (0x1)
+// CHECK-NEXT: Type: None (0x0)
+// CHECK-NEXT: Other: 0
+// CHECK-NEXT: Section: Undefined (0x0)
+// CHECK-NEXT: }
+// CHECK-NEXT: Symbol {
+// CHECK-NEXT: Name: __imp_??_R0?AVlogic_error at std@@@8 (35)
+// CHECK-NEXT: Value: 0x0
+// CHECK-NEXT: Size: 0
+// CHECK-NEXT: Binding: Global (0x1)
+// CHECK-NEXT: Type: None (0x0)
+// CHECK-NEXT: Other: 0
+// CHECK-NEXT: Section: Undefined (0x0)
+// CHECK-NEXT: }
+// CHECK-NEXT: Symbol {
+// CHECK-NEXT: Name: __imp_@??_R0PAVexception at std@@@8 (69)
+// CHECK-NEXT: Value: 0x0
+// CHECK-NEXT: Size: 0
+// CHECK-NEXT: Binding: Global (0x1)
+// CHECK-NEXT: Type: None (0x0)
+// CHECK-NEXT: Other: 0
+// CHECK-NEXT: Section: Undefined (0x0)
+// CHECK-NEXT: }
+// CHECK-NEXT: ]
--
1.8.4.2
Benoit Belley
Sr Principal Developer
M&E-Product Development Group
MAIN +1 514 393 1616
DIRECT +1 438 448 6304
FAX +1 514 393 0110
Twitter<http://twitter.com/autodesk>
Facebook<https://www.facebook.com/Autodesk>
Autodesk, Inc.
10 Duke Street
Montreal, Quebec, Canada H3C 2L7
www.autodesk.com<http://www.autodesk.com/>
[Description: Email_Signature_Logobar]
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20141210/5901b7c9/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 350F40DB-4457-4455-A632-0DF05738AF15[6].png
Type: image/png
Size: 4316 bytes
Desc: 350F40DB-4457-4455-A632-0DF05738AF15[6].png
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20141210/5901b7c9/attachment.png>