[llvm-branch-commits] [lld] Backport [LLD][COFF] Disallow importing DllMain from import libraries (#146610) (PR #146699)
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Wed Jul 2 07:14:26 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-platform-windows
Author: Alexandre Ganea (aganea)
<details>
<summary>Changes</summary>
This is a workaround for
https://github.com/llvm/llvm-project/issues/82050 by skipping the `DllMain` symbol if seen in aimport library. If this situation occurs, after this commit a warning will also be displayed. The warning can be silenced with `/ignore:exporteddllmain`
---
Full diff: https://github.com/llvm/llvm-project/pull/146699.diff
4 Files Affected:
- (modified) lld/COFF/Config.h (+1)
- (modified) lld/COFF/Driver.cpp (+2)
- (modified) lld/COFF/InputFiles.cpp (+39-1)
- (added) lld/test/COFF/exported-dllmain.test (+57)
``````````diff
diff --git a/lld/COFF/Config.h b/lld/COFF/Config.h
index 0c7c4e91402f1..424e9578395b3 100644
--- a/lld/COFF/Config.h
+++ b/lld/COFF/Config.h
@@ -313,6 +313,7 @@ struct Configuration {
bool warnDebugInfoUnusable = true;
bool warnLongSectionNames = true;
bool warnStdcallFixup = true;
+ bool warnExportedDllMain = true;
bool incremental = true;
bool integrityCheck = false;
bool killAt = false;
diff --git a/lld/COFF/Driver.cpp b/lld/COFF/Driver.cpp
index a669b7e9296f6..8b2fc9f23178f 100644
--- a/lld/COFF/Driver.cpp
+++ b/lld/COFF/Driver.cpp
@@ -1625,6 +1625,8 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
config->warnLocallyDefinedImported = false;
else if (s == "longsections")
config->warnLongSectionNames = false;
+ else if (s == "exporteddllmain")
+ config->warnExportedDllMain = false;
// Other warning numbers are ignored.
}
}
diff --git a/lld/COFF/InputFiles.cpp b/lld/COFF/InputFiles.cpp
index 7b105fb4c17a2..b470b2a8d9080 100644
--- a/lld/COFF/InputFiles.cpp
+++ b/lld/COFF/InputFiles.cpp
@@ -117,6 +117,35 @@ static coff_symbol_generic *cloneSymbol(COFFSymbolRef sym) {
}
}
+// Skip importing DllMain thunks from import libraries.
+static bool fixupDllMain(COFFLinkerContext &ctx, llvm::object::Archive *file,
+ const Archive::Symbol &sym, bool &skipDllMain) {
+ if (skipDllMain)
+ return true;
+ const Archive::Child &c =
+ CHECK(sym.getMember(), file->getFileName() +
+ ": could not get the member for symbol " +
+ toCOFFString(ctx, sym));
+ MemoryBufferRef mb =
+ CHECK(c.getMemoryBufferRef(),
+ file->getFileName() +
+ ": could not get the buffer for a child buffer of the archive");
+ if (identify_magic(mb.getBuffer()) == file_magic::coff_import_library) {
+ if (ctx.config.warnExportedDllMain) {
+ // We won't place DllMain symbols in the symbol table if they are
+ // coming from a import library. This message can be ignored with the flag
+ // '/ignore:exporteddllmain'
+ Warn(ctx)
+ << file->getFileName()
+ << ": skipping exported DllMain symbol [exporteddllmain]\nNOTE: this "
+ "might be a mistake when the DLL/library was produced.";
+ }
+ skipDllMain = true;
+ return true;
+ }
+ return false;
+}
+
ArchiveFile::ArchiveFile(COFFLinkerContext &ctx, MemoryBufferRef m)
: InputFile(ctx.symtab, ArchiveKind, m) {}
@@ -140,8 +169,17 @@ void ArchiveFile::parse() {
}
// Read the symbol table to construct Lazy objects.
- for (const Archive::Symbol &sym : file->symbols())
+ bool skipDllMain = false;
+ for (const Archive::Symbol &sym : file->symbols()) {
+ // If the DllMain symbol was exported by mistake, skip importing it
+ // otherwise we might end up with a import thunk in the final binary which
+ // is wrong.
+ if (sym.getName() == "__imp_DllMain" || sym.getName() == "DllMain") {
+ if (fixupDllMain(ctx, file.get(), sym, skipDllMain))
+ continue;
+ }
ctx.symtab.addLazyArchive(this, sym);
+ }
}
// Returns a buffer pointing to a member file containing a given symbol.
diff --git a/lld/test/COFF/exported-dllmain.test b/lld/test/COFF/exported-dllmain.test
new file mode 100644
index 0000000000000..fcf6ed1005379
--- /dev/null
+++ b/lld/test/COFF/exported-dllmain.test
@@ -0,0 +1,57 @@
+REQUIRES: x86
+RUN: split-file %s %t.dir && cd %t.dir
+
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows a.s -o a.obj
+
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows b1.s -o b1.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows b2.s -o b2.obj
+
+### This is the line where our problem occurs. Here, we export the DllMain symbol which shouldn't happen normally.
+RUN: lld-link b1.obj b2.obj -out:b.dll -dll -implib:b.lib -entry:DllMain -export:bar -export:DllMain
+
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows c.s -o c.obj
+RUN: lld-link -lib c.obj -out:c.lib
+
+### Later, if b.lib is provided before other libs/objs that export DllMain statically, we previously were using the dllimported DllMain from b.lib, which is wrong.
+RUN: lld-link a.obj b.lib c.lib -dll -out:out.dll -entry:DllMain 2>&1 | FileCheck -check-prefix=WARN %s
+RUN: lld-link a.obj b.lib c.lib -dll -out:out.dll -entry:DllMain -ignore:exporteddllmain 2>&1 | FileCheck -check-prefix=IGNORED --allow-empty %s
+RUN: llvm-objdump --private-headers -d out.dll | FileCheck -check-prefix=DISASM %s
+
+WARN: lld-link: warning: b.lib: skipping exported DllMain symbol [exporteddllmain]
+IGNORED-NOT: lld-link: warning: b.lib: skipping exported DllMain symbol [exporteddllmain]
+
+DISASM: The Import Tables:
+DISASM: DLL Name: b.dll
+DISASM-NOT: DllMain
+DISASM: bar
+DISASM: Disassembly of section .text:
+DISASM-EMPTY:
+DISASM: b8 01 00 00 00 movl $0x1, %eax
+DISASM-NEXT: c3 retq
+
+#--- a.s
+ .text
+ .globl foo
+foo:
+ call *__imp_bar(%rip)
+ ret
+
+#--- b1.s
+ .text
+ .globl bar
+bar:
+ ret
+
+#--- b2.s
+ .text
+ .globl DllMain
+DllMain:
+ xor %eax, %eax
+ ret
+
+#--- c.s
+ .text
+ .globl DllMain
+DllMain:
+ movl $1, %eax
+ ret
``````````
</details>
https://github.com/llvm/llvm-project/pull/146699
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