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[LLD][COFF] add __{data,bss}_{start,end}__ symbols for Cygwin support #136180

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Merged
merged 1 commit into from
May 2, 2025
Merged

[LLD][COFF] add __{data,bss}_{start,end}__ symbols for Cygwin support #136180

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5 changes: 5 additions & 0 deletions lld/COFF/Driver.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2028,6 +2028,7 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
parseMerge(".ctors=.rdata");
parseMerge(".dtors=.rdata");
parseMerge(".CRT=.rdata");
parseMerge(".data_cygwin_nocopy=.data");
}

// Handle /section
Expand Down Expand Up @@ -2484,6 +2485,10 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
if (config->mingw) {
symtab.addAbsolute(symtab.mangle("__CTOR_LIST__"), 0);
symtab.addAbsolute(symtab.mangle("__DTOR_LIST__"), 0);
symtab.addAbsolute("__data_start__", 0);
symtab.addAbsolute("__data_end__", 0);
symtab.addAbsolute("__bss_start__", 0);
symtab.addAbsolute("__bss_end__", 0);
}
if (config->debug || config->buildIDHash != BuildIDHash::None)
if (symtab.findUnderscore("__buildid"))
Expand Down
33 changes: 31 additions & 2 deletions lld/COFF/Writer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -240,6 +240,7 @@ class Writer {
void createRuntimePseudoRelocs();
void createECChunks();
void insertCtorDtorSymbols();
void insertBssDataStartEndSymbols();
void markSymbolsWithRelocations(ObjFile *file, SymbolRVASet &usedSymbols);
void createGuardCFTables();
void markSymbolsForRVATable(ObjFile *file,
Expand Down Expand Up @@ -315,6 +316,7 @@ class Writer {

OutputSection *textSec;
OutputSection *hexpthkSec;
OutputSection *bssSec;
OutputSection *rdataSec;
OutputSection *buildidSec;
OutputSection *dataSec;
Expand Down Expand Up @@ -1077,7 +1079,7 @@ void Writer::createSections() {
textSec = createSection(".text", code | r | x);
if (isArm64EC(ctx.config.machine))
hexpthkSec = createSection(".hexpthk", code | r | x);
createSection(".bss", bss | r | w);
bssSec = createSection(".bss", bss | r | w);
rdataSec = createSection(".rdata", data | r);
buildidSec = createSection(".buildid", data | r);
dataSec = createSection(".data", data | r | w);
Expand Down Expand Up @@ -1260,8 +1262,10 @@ void Writer::createMiscChunks() {
if (config->autoImport)
createRuntimePseudoRelocs();

if (config->mingw)
if (config->mingw) {
insertCtorDtorSymbols();
insertBssDataStartEndSymbols();
}
}

// Create .idata section for the DLL-imported symbol table.
Expand Down Expand Up @@ -2381,6 +2385,31 @@ void Writer::insertCtorDtorSymbols() {
}
}

// MinGW (really, Cygwin) specific.
// The Cygwin startup code uses __data_start__ __data_end__ __bss_start__
// and __bss_end__ to know what to copy during fork emulation.
void Writer::insertBssDataStartEndSymbols() {
if (!dataSec->chunks.empty()) {
Symbol *dataStartSym = ctx.symtab.find("__data_start__");
Symbol *dataEndSym = ctx.symtab.find("__data_end__");
Chunk *endChunk = dataSec->chunks.back();
replaceSymbol<DefinedSynthetic>(dataStartSym, dataStartSym->getName(),
dataSec->chunks.front());
replaceSymbol<DefinedSynthetic>(dataEndSym, dataEndSym->getName(), endChunk,
endChunk->getSize());
}

if (!bssSec->chunks.empty()) {
Symbol *bssStartSym = ctx.symtab.find("__bss_start__");
Symbol *bssEndSym = ctx.symtab.find("__bss_end__");
Chunk *endChunk = bssSec->chunks.back();
replaceSymbol<DefinedSynthetic>(bssStartSym, bssStartSym->getName(),
bssSec->chunks.front());
replaceSymbol<DefinedSynthetic>(bssEndSym, bssEndSym->getName(), endChunk,
endChunk->getSize());
}
}

// Handles /section options to allow users to overwrite
// section attributes.
void Writer::setSectionPermissions() {
Expand Down
99 changes: 99 additions & 0 deletions lld/test/COFF/cygwin-symbols.s
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@@ -0,0 +1,99 @@
# REQUIRES: x86
# RUN: split-file %s %t.dir && cd %t.dir

# RUN: llvm-mc -triple=x86_64-windows-cygnus -filetype=obj -o data-no-bss.obj data-no-bss.s
# RUN: lld-link -lldmingw -entry:main data-no-bss.obj -out:data-no-bss.exe
# RUN: llvm-objdump -s data-no-bss.exe | FileCheck --check-prefix=DATANOBSS %s

# RUN: llvm-mc -triple=x86_64-windows-cygnus -filetype=obj -o bss-no-data.obj bss-no-data.s
# RUN: lld-link -lldmingw -entry:main bss-no-data.obj -out:bss-no-data.exe
# RUN: llvm-objdump -s bss-no-data.exe | FileCheck --check-prefix=BSSNODATA %s

# RUN: llvm-mc -triple=x86_64-windows-cygnus -filetype=obj -o data-and-bss.obj data-and-bss.s
# RUN: lld-link -lldmingw -entry:main data-and-bss.obj -out:data-and-bss.exe
# RUN: llvm-objdump -s data-and-bss.exe | FileCheck --check-prefix=DATAANDBSS %s

#--- data-no-bss.s
.globl main
main:
nop

.data
.quad 1
.byte 2

.section .data_cygwin_nocopy, "w"
.align 4
.quad 3
.byte 4

.section .test, "w"
.quad __data_start__
.quad __data_end__
.quad __bss_start__
.quad __bss_end__

#--- bss-no-data.s
.globl main
main:
nop

.bss
.zero 8192

.section .test, "w"
.quad __data_start__
.quad __data_end__
.quad __bss_start__
.quad __bss_end__

#--- data-and-bss.s
.globl main
main:
nop

.data
.quad 1
.byte 2

.section .data_cygwin_nocopy, "w"
.align 4
.quad 3
.byte 4

.bss
.zero 8192

.section .test, "w"
.quad __data_start__
.quad __data_end__
.quad __bss_start__
.quad __bss_end__

# DATANOBSS: Contents of section .data:
# DATANOBSS-NEXT: 140003000 01000000 00000000 02000000 03000000
# DATANOBSS-NEXT: 140003010 00000000 04
# __data_start__ pointing at 0x140003000 and
# __data_end__ pointing at 0x140003009.
# DATANOBSS-NEXT: Contents of section .test:
# DATANOBSS-NEXT: 140004000 00300040 01000000 09300040 01000000
# DATANOBSS-NEXT: 140004010 18300040 01000000 18300040 01000000

# __bss_start__ pointing at 0x140003000 and
# __bss_end__ pointing at 0x140005000.
# BSSNODATA-NOT: Contents of section .data:
# BSSNODATA: Contents of section .test:
# BSSNODATA-NEXT: 140005000 00300040 01000000 00300040 01000000
# BSSNODATA-NEXT: 140005010 00300040 01000000 00500040 01000000

# DATAANDBSS: Contents of section .data:
# DATAANDBSS-NEXT: 140003000 01000000 00000000 02000000 03000000
# DATAANDBSS-NEXT: 140003010 00000000 04000000 00000000 00000000
# __data_start__ pointing at 0x140003000 and
# __data_end__ pointing at 0x140003009.
# __bss_start__ pointing at 0x140003018 and
# __bss_end__ pointing at 0x140005018.
# DATAANDBSS: 1400031f0 00000000 00000000 00000000 00000000
# DATAANDBSS-NEXT: Contents of section .test:
# DATAANDBSS-NEXT: 140006000 00300040 01000000 09300040 01000000
# DATAANDBSS-NEXT: 140006010 18300040 01000000 18500040 01000000