[lld] [LLD][COFF] Avoid resolving symbols with -alternatename if the target is undefined (PR #149496)
Jacek Caban via llvm-commits
llvm-commits at lists.llvm.org
Mon Jul 28 08:56:37 PDT 2025
https://github.com/cjacek updated https://github.com/llvm/llvm-project/pull/149496
>From 31c4c144b96645ff5e6f41d09459cea006106a18 Mon Sep 17 00:00:00 2001
From: Jacek Caban <jacek at codeweavers.com>
Date: Fri, 18 Jul 2025 12:27:26 +0200
Subject: [PATCH] [LLD][COFF] Avoid resolving symbols with -alternatename if
the target is undefined
This change fixes an issue with the use of -alternatename in the MSVC CRT, where both mangled
and demangled symbol names are specified. Without this patch, the demangled name could be resolved
to an anti-dependency alias of the target. Since chaining anti-dependency aliases is not allowed,
this results in an undefined symbol.
The root cause isn't specific to ARM64EC, it can affect other targets as well, even when
anti-dependency aliases aren't involved. The accompanying test case demonstrates a scenario where
the symbol could be resolved from an archive. However, because the archive member is pulled in
after the first pass of alternate name resolution, and archive members don't override weak aliases,
eager resolution would incorrectly skip it.
---
lld/COFF/SymbolTable.cpp | 14 ++++++++-
lld/test/COFF/alternatename-alias.s | 15 ++++++++++
lld/test/COFF/alternatename-antidep.s | 16 ++++++++++
lld/test/COFF/alternatename-lib.s | 43 +++++++++++++++++++++++++++
lld/test/COFF/arm64ec-altnames.s | 39 ++++++++++++++++++++++++
5 files changed, 126 insertions(+), 1 deletion(-)
create mode 100644 lld/test/COFF/alternatename-alias.s
create mode 100644 lld/test/COFF/alternatename-antidep.s
create mode 100644 lld/test/COFF/alternatename-lib.s
diff --git a/lld/COFF/SymbolTable.cpp b/lld/COFF/SymbolTable.cpp
index 1cf750393e6b3..189e75dfc3ff5 100644
--- a/lld/COFF/SymbolTable.cpp
+++ b/lld/COFF/SymbolTable.cpp
@@ -1364,7 +1364,19 @@ void SymbolTable::resolveAlternateNames() {
!isArm64ECMangledFunctionName(u->getName()))
continue;
}
- u->setWeakAlias(addUndefined(to));
+
+ // Check if the destination symbol is defined. If not, skip it.
+ // It may still be resolved later if more input files are added.
+ // Also skip anti-dependency targets, as they can't be chained anyway.
+ Symbol *toSym = find(to);
+ if (!toSym)
+ continue;
+ auto toUndef = dyn_cast<Undefined>(toSym);
+ if (toUndef && (!toUndef->weakAlias || toUndef->isAntiDep))
+ continue;
+ if (toSym->isLazy())
+ forceLazy(toSym);
+ u->setWeakAlias(toSym);
}
}
}
diff --git a/lld/test/COFF/alternatename-alias.s b/lld/test/COFF/alternatename-alias.s
new file mode 100644
index 0000000000000..bd0a861380e94
--- /dev/null
+++ b/lld/test/COFF/alternatename-alias.s
@@ -0,0 +1,15 @@
+// REQUIRES: x86
+
+// Check that a weak alias can be used as an alternate name target.
+// RUN: llvm-mc -filetype=obj -triple=x86_64-windows %s -o %t.obj
+// RUN: lld-link -dll -noentry %t.obj -alternatename:sym=altsym
+
+ .data
+ .rva sym
+
+ .weak altsym
+ .set altsym,a
+
+ .globl a
+a:
+ .word 1
diff --git a/lld/test/COFF/alternatename-antidep.s b/lld/test/COFF/alternatename-antidep.s
new file mode 100644
index 0000000000000..1188a9b75d481
--- /dev/null
+++ b/lld/test/COFF/alternatename-antidep.s
@@ -0,0 +1,16 @@
+// REQUIRES: x86
+
+// Check that an anti-dependency alias can't be used as an alternate name target.
+// RUN: llvm-mc -filetype=obj -triple=x86_64-windows %s -o %t.obj
+// RUN: not lld-link -dll -noentry %t.obj -alternatename:sym=altsym 2>&1 | FileCheck %s
+// CHECK: error: undefined symbol: sym
+
+ .data
+ .rva sym
+
+ .weak_anti_dep altsym
+ .set altsym,a
+
+ .globl a
+a:
+ .word 1
diff --git a/lld/test/COFF/alternatename-lib.s b/lld/test/COFF/alternatename-lib.s
new file mode 100644
index 0000000000000..206fe6bc23978
--- /dev/null
+++ b/lld/test/COFF/alternatename-lib.s
@@ -0,0 +1,43 @@
+// REQUIRES: x86
+// RUN: split-file %s %t.dir && cd %t.dir
+
+// RUN: llvm-mc -filetype=obj -triple=x86_64-windows refab.s -o refab.obj
+// RUN: llvm-mc -filetype=obj -triple=x86_64-windows aa.s -o aa.obj
+// RUN: llvm-mc -filetype=obj -triple=x86_64-windows b.s -o b.obj
+// RUN: llvm-mc -filetype=obj -triple=x86_64-windows antidep.s -o antidep.obj
+// RUN: llvm-lib -out:aa.lib aa.obj
+// RUN: llvm-lib -out:b.lib b.obj
+
+// Check that -alternatename with an undefined target does not prevent the symbol from being resolved to a library,
+// once another alternate name is resolved and pulls in the source symbol.
+// RUN: lld-link -out:out.dll -dll -noentry -machine:amd64 refab.obj aa.lib -alternatename:a=aa -alternatename:b=undef
+
+// Check that -alternatename with an anti-dependency target does not prevent the symbol from being resolved to a library,
+// after another alternate name is resolved and pulls in the source symbol.
+// RUN: lld-link -out:out2.dll -dll -noentry -machine:amd64 antidep.obj refab.obj aa.lib -alternatename:a=aa -alternatename:b=u
+
+#--- refab.s
+ .data
+ .rva a
+ .rva b
+
+#--- aa.s
+ .globl aa
+aa:
+ .word 1
+
+ .section .drectve, "yn"
+ .ascii "/defaultlib:b.lib"
+
+#--- b.s
+ .globl b
+b:
+ .word 2
+
+#--- antidep.s
+ .weak_anti_dep u
+ .set u,d
+
+ .globl d
+d:
+ .word 3
diff --git a/lld/test/COFF/arm64ec-altnames.s b/lld/test/COFF/arm64ec-altnames.s
index b2abb24efe4c3..cca778ab8dc64 100644
--- a/lld/test/COFF/arm64ec-altnames.s
+++ b/lld/test/COFF/arm64ec-altnames.s
@@ -2,6 +2,7 @@ REQUIRES: aarch64
RUN: split-file %s %t.dir && cd %t.dir
RUN: llvm-mc -filetype=obj -triple=arm64ec-windows ext.s -o ext.obj
+RUN: llvm-mc -filetype=obj -triple=arm64ec-windows ext-mangled.s -o ext-mangled.obj
RUN: llvm-mc -filetype=obj -triple=arm64ec-windows impl.s -o impl.obj
RUN: llvm-mc -filetype=obj -triple=arm64ec-windows impl-cpp.s -o impl-cpp.obj
RUN: llvm-mc -filetype=obj -triple=arm64ec-windows %S/Inputs/loadconfig-arm64ec.s -o loadconfig.obj
@@ -49,6 +50,20 @@ RUN: lld-link -machine:arm64ec -dll -noentry -out:out4.dll impl-cpp.obj loadconf
RUN: llvm-objdump -d out4.dll | FileCheck --check-prefix=DISASM %s
RUN: llvm-readobj --hex-dump=.test out4.dll | FileCheck --check-prefix=TESTSEC %s
+# Check that when both mangled and demangled alternate names are used,
+# only the one whose target is defined is used (the mangled one in this case).
+
+RUN: lld-link -machine:arm64ec -dll -noentry -out:out5.dll ext-mangled.obj loadconfig.obj "-alternatename:#func=#altsym" -alternatename:func=altsym
+RUN: llvm-objdump -d out5.dll | FileCheck --check-prefix=DISASM %s
+RUN: llvm-readobj --hex-dump=.test out5.dll | FileCheck --check-prefix=TESTSEC %s
+
+# Check that when both mangled and demangled alternate names are used,
+# only the one whose target is defined is used (the demangled one in this case).
+
+RUN: lld-link -machine:arm64ec -dll -noentry -out:out6.dll ext.obj loadconfig.obj "-alternatename:#func=#altsym" -alternatename:func=altsym
+RUN: llvm-objdump -d out6.dll | FileCheck --check-prefix=DISASM2 %s
+RUN: llvm-readobj --hex-dump=.test out6.dll | FileCheck --check-prefix=TESTSEC2 %s
+
#--- ext.s
.weak_anti_dep func
.set func, "#func"
@@ -70,6 +85,30 @@ altsym:
mov w0, #1
ret
+#--- ext-mangled.s
+ .weak_anti_dep func
+.set func, "#func"
+ .weak_anti_dep "#func"
+.set "#func", thunksym
+
+ .section .test, "r"
+ .rva func
+ .rva "#func"
+
+ .section .thnk,"xr",discard,thunksym
+thunksym:
+ mov w0, #2
+ ret
+
+ .section .text,"xr",discard,"#altsym"
+ .globl "#altsym"
+"#altsym":
+ mov w0, #1
+ ret
+
+ .weak_anti_dep altsym
+ .set altsym,"#altsym"
+
#--- impl.s
.weak_anti_dep func
.set func, "#func"
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