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[LLD][COFF] Allow overriding EC alias symbols with alternate names (#113456)
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3 files changed

+128
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3 files changed

+128
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‎lld/COFF/Driver.cpp

Lines changed: 13 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -2518,9 +2518,19 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
25182518
Symbol *sym = ctx.symtab.find(from);
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if (!sym)
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continue;
2521-
if (auto *u = dyn_cast<Undefined>(sym))
2522-
if (!u->weakAlias)
2523-
u->setWeakAlias(ctx.symtab.addUndefined(to));
2521+
if (auto *u = dyn_cast<Undefined>(sym)) {
2522+
if (u->weakAlias) {
2523+
// On ARM64EC, anti-dependency aliases are treated as undefined
2524+
// symbols unless a demangled symbol aliases a defined one, which is
2525+
// part of the implementation.
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if (!isArm64EC(ctx.config.machine) || !u->isAntiDep)
2527+
continue;
2528+
if (!isa<Undefined>(u->weakAlias) &&
2529+
!isArm64ECMangledFunctionName(u->getName()))
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continue;
2531+
}
2532+
u->setWeakAlias(ctx.symtab.addUndefined(to));
2533+
}
25242534
}
25252535

25262536
// If any inputs are bitcode files, the LTO code generator may create

‎lld/test/COFF/arm64ec-altnames.s

Lines changed: 109 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,109 @@
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REQUIRES: aarch64
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RUN: split-file %s %t.dir && cd %t.dir
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RUN: llvm-mc -filetype=obj -triple=arm64ec-windows ext.s -o ext.obj
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RUN: llvm-mc -filetype=obj -triple=arm64ec-windows impl.s -o impl.obj
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RUN: llvm-mc -filetype=obj -triple=arm64ec-windows impl-cpp.s -o impl-cpp.obj
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RUN: llvm-mc -filetype=obj -triple=arm64ec-windows %S/Inputs/loadconfig-arm64ec.s -o loadconfig.obj
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# Ensure -alternatename can change a mangled function symbol aliasing a defined symbol (typically a guest exit thunk).
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RUN: lld-link -machine:arm64ec -dll -noentry -out:out1.dll ext.obj loadconfig.obj "-alternatename:#func=altsym"
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RUN: llvm-objdump -d out1.dll | FileCheck --check-prefix=DISASM %s
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DISASM: 0000000180001000 <.text>:
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DISASM-NEXT: 180001000: 52800020 mov w0, #0x1 // =1
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DISASM-NEXT: 180001004: d65f03c0 ret
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DISASM-NOT: .thnk
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RUN: llvm-readobj --hex-dump=.test out1.dll | FileCheck --check-prefix=TESTSEC %s
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TESTSEC: 0x180004000 00100000 00100000
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# Ensure -alternatename can change a demangled function symbol aliasing an anti-dependency symbol.
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RUN: lld-link -machine:arm64ec -dll -noentry -out:out2.dll ext.obj loadconfig.obj -alternatename:func=altsym
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RUN: llvm-objdump -d out2.dll | FileCheck --check-prefix=DISASM2 %s
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DISASM2: Disassembly of section .text:
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DISASM2-EMPTY:
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DISASM2-NEXT: 0000000180001000 <.text>:
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DISASM2-NEXT: 180001000: 52800020 mov w0, #0x1 // =1
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DISASM2-NEXT: 180001004: d65f03c0 ret
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DISASM2-EMPTY:
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DISASM2-NEXT: Disassembly of section .thnk:
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DISASM2-EMPTY:
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DISASM2-NEXT: 0000000180005000 <.thnk>:
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DISASM2-NEXT: 180005000: 52800040 mov w0, #0x2 // =2
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DISASM2-NEXT: 180005004: d65f03c0 ret
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RUN: llvm-readobj --hex-dump=.test out2.dll | FileCheck --check-prefix=TESTSEC2 %s
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TESTSEC2: 0x180004000 00100000 00500000
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# Ensure -alternatename cannot modify a demangled function symbol aliasing a defined symbol.
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RUN: lld-link -machine:arm64ec -dll -noentry -out:out3.dll impl.obj loadconfig.obj -alternatename:func=altsym
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RUN: llvm-objdump -d out3.dll | FileCheck --check-prefix=DISASM %s
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RUN: llvm-readobj --hex-dump=.test out3.dll | FileCheck --check-prefix=TESTSEC %s
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RUN: lld-link -machine:arm64ec -dll -noentry -out:out4.dll impl-cpp.obj loadconfig.obj -alternatename:func=altsym
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RUN: llvm-objdump -d out4.dll | FileCheck --check-prefix=DISASM %s
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RUN: llvm-readobj --hex-dump=.test out4.dll | FileCheck --check-prefix=TESTSEC %s
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#--- ext.s
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.weak_anti_dep func
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.set func, "#func"
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.weak_anti_dep "#func"
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.set "#func", thunksym
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.section .test, "r"
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.rva func
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.rva "#func"
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.section .thnk,"xr",discard,thunksym
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thunksym:
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mov w0, #2
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ret
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.section .text,"xr",discard,altsym
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.globl altsym
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altsym:
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mov w0, #1
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ret
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#--- impl.s
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.weak_anti_dep func
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.set func, "#func"
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.section .test, "r"
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.rva func
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.rva "#func"
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.section .text,"xr",discard,"#func"
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"#func":
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mov w0, #1
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ret
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.section .text,"xr",discard,altsym
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.globl altsym
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altsym:
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mov w0, #2
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ret
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#--- impl-cpp.s
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.weak_anti_dep func
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.set func, "?func@@$$hYAXXZ"
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.section .test, "r"
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.rva func
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.rva "?func@@$$hYAXXZ"
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.section .text,"xr",discard,"?func@@$$hYAXXZ"
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"?func@@$$hYAXXZ":
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mov w0, #1
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ret
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105+
.section .text,"xr",discard,altsym
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.globl altsym
107+
altsym:
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mov w0, #2
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ret

‎llvm/include/llvm/IR/Mangler.h

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -61,6 +61,12 @@ std::optional<std::string> getArm64ECMangledFunctionName(StringRef Name);
6161
/// mangled.
6262
std::optional<std::string> getArm64ECDemangledFunctionName(StringRef Name);
6363

64+
/// Check if an ARM64EC function name is mangled.
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bool inline isArm64ECMangledFunctionName(StringRef Name) {
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return Name[0] == '#' ||
67+
(Name[0] == '?' && Name.find("$$h") != StringRef::npos);
68+
}
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6470
} // End llvm namespace
6571

6672
#endif

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