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[lld] [MTE] Drop MTE globals for fully static executables, not ban #68217

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Merged
merged 4 commits into from
Oct 10, 2023
Merged

[lld] [MTE] Drop MTE globals for fully static executables, not ban #68217

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79ab3d9
[lld] [MTE] Drop MTE globals for fully static executables, not ban
hctim Oct 4, 2023
caacf44
Move metadata section discarding inside of the input file parsing.
hctim Oct 6, 2023
1595b1e
clang-format
hctim Oct 6, 2023
adbdbd4
Remove -Bstatic from test.
hctim Oct 10, 2023
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3 changes: 1 addition & 2 deletions lld/ELF/Driver.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3029,8 +3029,7 @@ void LinkerDriver::link(opt::InputArgList &args) {
// partition.
copySectionsIntoPartitions();

if (config->emachine == EM_AARCH64 &&
config->androidMemtagMode != ELF::NT_MEMTAG_LEVEL_NONE) {
if (canHaveMemtagGlobals()) {
llvm::TimeTraceScope timeScope("Process memory tagged symbols");
createTaggedSymbols(ctx.objectFiles);
}
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10 changes: 10 additions & 0 deletions lld/ELF/InputFiles.cpp
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Expand Up @@ -624,6 +624,16 @@ template <class ELFT> void ObjFile<ELFT>::parse(bool ignoreComdats) {
}
}

// Producing a static binary with MTE globals is not currently supported,
// remove all SHT_AARCH64_MEMTAG_GLOBALS_STATIC sections as they're unused
// medatada, and we don't want them to end up in the output file for static
// executables.
if (sec.sh_type == SHT_AARCH64_MEMTAG_GLOBALS_STATIC &&
!canHaveMemtagGlobals()) {
this->sections[i] = &InputSection::discarded;
continue;
}

if (sec.sh_type != SHT_GROUP)
continue;
StringRef signature = getShtGroupSignature(objSections, sec);
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18 changes: 13 additions & 5 deletions lld/ELF/Writer.cpp
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Expand Up @@ -251,6 +251,18 @@ void elf::addReservedSymbols() {
ElfSym::edata2 = add("_edata", -1);
}

// Fully static executables don't support MTE globals at this point in time, as
// we currently rely on:
// - A dynamic loader to process relocations, and
// - Dynamic entries.
// This restriction could be removed in future by re-using some of the ideas
// that ifuncs use in fully static executables.
bool elf::canHaveMemtagGlobals() {
return config->emachine == EM_AARCH64 &&
config->androidMemtagMode != ELF::NT_MEMTAG_LEVEL_NONE &&
(config->relocatable || config->shared || needsInterpSection());
}

static OutputSection *findSection(StringRef name, unsigned partition = 1) {
for (SectionCommand *cmd : script->sectionCommands)
if (auto *osd = dyn_cast<OutputDesc>(cmd))
Expand Down Expand Up @@ -345,11 +357,7 @@ template <class ELFT> void elf::createSyntheticSections() {
std::make_unique<SymbolTableSection<ELFT>>(*part.dynStrTab);
part.dynamic = std::make_unique<DynamicSection<ELFT>>();

if (config->emachine == EM_AARCH64 &&
config->androidMemtagMode != ELF::NT_MEMTAG_LEVEL_NONE) {
if (!config->relocatable && !config->shared && !needsInterpSection())
error("--android-memtag-mode is incompatible with fully-static "
"executables (-static)");
if (canHaveMemtagGlobals()) {
part.memtagAndroidNote = std::make_unique<MemtagAndroidNote>();
add(*part.memtagAndroidNote);
part.memtagDescriptors = std::make_unique<MemtagDescriptors>();
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2 changes: 2 additions & 0 deletions lld/ELF/Writer.h
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Expand Up @@ -56,6 +56,8 @@ uint8_t getMipsFpAbiFlag(uint8_t oldFlag, uint8_t newFlag,
bool isMipsN32Abi(const InputFile *f);
bool isMicroMips();
bool isMipsR6();

bool canHaveMemtagGlobals();
} // namespace lld::elf

#endif
35 changes: 35 additions & 0 deletions lld/test/ELF/Inputs/aarch64-memtag-globals.s
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Expand Up @@ -380,3 +380,38 @@ global_extern_const_definition_but_nonconst_import:
global_extern_untagged_definition_but_tagged_import:
.word 0
.size global_extern_untagged_definition_but_tagged_import, 4

#--- input_3.s
## Generated with:
##
## - clang <input_file.c> -fsanitize=memtag-globals -O2 -S -o - \
## --target=aarch64-linux-android31 -fno-asynchronous-unwind-tables
##
## <input_file.c> contents:
##
## int global_extern_outside_this_dso;
##
## int main() {
## return 0;
## }

.text
.file "main.c"
.globl main // -- Begin function main
.p2align 2
.type main,@function
main: // @main
// %bb.0: // %entry
mov w0, wzr
ret
.Lfunc_end0:
.size main, .Lfunc_end0-main
// -- End function
.memtag global_extern_outside_this_dso // @global_extern_outside_this_dso
.type global_extern_outside_this_dso,@object
.bss
.globl global_extern_outside_this_dso
.p2align 4, 0x0
global_extern_outside_this_dso:
.zero 16
.size global_extern_outside_this_dso, 16
31 changes: 27 additions & 4 deletions lld/test/ELF/aarch64-memtag-globals.s
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Expand Up @@ -73,10 +73,33 @@ Symbols:
# RUN: %t1.o %t2.o -o %t1.so 2>&1 | FileCheck %s --check-prefix=CHECK-DYNRELOC
# CHECK-DYNRELOC: --apply-dynamic-relocs cannot be used with MTE globals

## And ensure that fully-static executables are banned.
# RUN: not ld.lld --static --android-memtag-mode=sync \
# RUN: %t1.o %t2.o -o %t1.so 2>&1 | FileCheck %s --check-prefix=CHECK-NOSTATIC
# CHECK-NOSTATIC: --android-memtag-mode is incompatible with fully-static executables (-static)
## Ensure that fully statically linked executables just simply drop the MTE
## globals stuff: special relocations, data in the place to be relocated,
## dynamic entries, etc.
# RUN: llvm-mc --filetype=obj -triple=aarch64-none-linux-android \
# RUN: %t/input_3.s -o %t3.o
# RUN: ld.lld -static --android-memtag-mode=sync %t1.o %t2.o %t3.o -o %t.static.so
# RUN: llvm-readelf -s --section-headers --relocs --memtag %t.static.so | \
# RUN: FileCheck %s --check-prefix=CHECK-STATIC
# CHECK-STATIC-NOT: .memtag.globals.static
# CHECK-STATIC-NOT: DT_AARCH64_MEMTAG_

# CHECK-STATIC: There are no relocations in this file
# CHECK-STATIC: Memtag Dynamic Entries:
# CHECK-STATIC-NEXT: < none found >

# RUN: llvm-objdump -tDz %t.static.so | FileCheck %s --check-prefix=CHECK-STATIC-SPECIAL-RELOCS
# CHECK-STATIC-SPECIAL-RELOCS: [[#%x,HIDDEN_GLOBAL_ADDR:]] {{.*}} .bss {{0*}}10 hidden_global
# CHECK-STATIC-SPECIAL-RELOCS: <pointer_to_hidden_global_end>:
# CHECK-STATIC-SPECIAL-RELOCS-NEXT: .word 0x{{0*}}[[#HIDDEN_GLOBAL_ADDR + 12]]
# CHECK-STATIC-SPECIAL-RELOCS-NEXT: .word 0x00000000
# CHECK-STATIC-SPECIAL-RELOCS-NEXT: .word 0x00000000
# CHECK-STATIC-SPECIAL-RELOCS-NEXT: .word 0x00000000
# CHECK-STATIC-SPECIAL-RELOCS: <pointer_past_hidden_global_end>:
# CHECK-STATIC-SPECIAL-RELOCS-NEXT: .word 0x{{0*}}[[#HIDDEN_GLOBAL_ADDR + 16]]
# CHECK-STATIC-SPECIAL-RELOCS-NEXT: .word 0x00000000
# CHECK-STATIC-SPECIAL-RELOCS-NEXT: .word 0x00000000
# CHECK-STATIC-SPECIAL-RELOCS-NEXT: .word 0x00000000

# CHECK: Symbol table '.dynsym' contains
# CHECK-DAG: [[#%x,GLOBAL:]] 32 OBJECT GLOBAL DEFAULT [[#]] global{{$}}
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