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[lld] [MTE] Add DT_AARCH64_MEMTAG_* dynamic entries, and small cleanup
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Adds the new AArch64-ABI dynamic entry generation to LLD. This will
allow Android to move from the Android-specific ELF note onto the
dynamic entries.

Change the behaviour of an unspecified --android-memtag-mode. Now, when
unspecified, this will print a warning that you're doing a no-op, rather
than implicitly turning on sync mode. This is important for MTE globals
later, where a binary containing static tagged global descriptors
shouldn't have MTE turned on without specific intent being passed to the
linker.

For now, continue to emit the Android ELF note by default. In future, we
can probably make it only emit the note when provided a flag.

Do a quick NFC-cleanup of the ELF note while we're here. It doesn't
change anything about the ELF note itself, but makes it more clear to
the reader of the code what alignment requirements are being (previously
implicitly) met.

Reviewed By: fmayer, MaskRay

Differential Revision: https://reviews.llvm.org/D143769
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@hctim
hctim committed Mar 1, 2023
1 parent 4e7d40e commit c574e93
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Showing 3 changed files with 63 additions and 44 deletions.
19 changes: 14 additions & 5 deletions lld/ELF/Driver.cpp
View file
Expand Up @@ -736,15 +736,24 @@ static StringRef getDynamicLinker(opt::InputArgList &args) {

static int getMemtagMode(opt::InputArgList &args) {
StringRef memtagModeArg = args.getLastArgValue(OPT_android_memtag_mode);
if (memtagModeArg.empty()) {
if (config->androidMemtagStack)
warn("--android-memtag-mode is unspecified, leaving "
"--android-memtag-stack a no-op");
else if (config->androidMemtagHeap)
warn("--android-memtag-mode is unspecified, leaving "
"--android-memtag-heap a no-op");
return ELF::NT_MEMTAG_LEVEL_NONE;
}

if (!config->androidMemtagHeap && !config->androidMemtagStack) {
if (!memtagModeArg.empty())
error("when using --android-memtag-mode, at least one of "
"--android-memtag-heap or "
"--android-memtag-stack is required");
error("when using --android-memtag-mode, at least one of "
"--android-memtag-heap or "
"--android-memtag-stack is required");
return ELF::NT_MEMTAG_LEVEL_NONE;
}

if (memtagModeArg == "sync" || memtagModeArg.empty())
if (memtagModeArg == "sync")
return ELF::NT_MEMTAG_LEVEL_SYNC;
if (memtagModeArg == "async")
return ELF::NT_MEMTAG_LEVEL_ASYNC;
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18 changes: 12 additions & 6 deletions lld/ELF/SyntheticSections.cpp
View file
Expand Up @@ -1441,6 +1441,12 @@ DynamicSection<ELFT>::computeContents() {
addInt(DT_AARCH64_BTI_PLT, 0);
if (config->zPacPlt)
addInt(DT_AARCH64_PAC_PLT, 0);

if (config->androidMemtagMode != ELF::NT_MEMTAG_LEVEL_NONE) {
addInt(DT_AARCH64_MEMTAG_MODE, config->androidMemtagMode == NT_MEMTAG_LEVEL_ASYNC);
addInt(DT_AARCH64_MEMTAG_HEAP, config->androidMemtagHeap);
addInt(DT_AARCH64_MEMTAG_STACK, config->androidMemtagStack);
}
}

addInSec(DT_SYMTAB, *part.dynSymTab);
Expand Down Expand Up @@ -3835,16 +3841,16 @@ void InStruct::reset() {

constexpr char kMemtagAndroidNoteName[] = "Android";
void MemtagAndroidNote::writeTo(uint8_t *buf) {
static_assert(sizeof(kMemtagAndroidNoteName) == 8,
"ABI check for Android 11 & 12.");
assert((config->androidMemtagStack || config->androidMemtagHeap) &&
"Should only be synthesizing a note if heap || stack is enabled.");
static_assert(
sizeof(kMemtagAndroidNoteName) == 8,
"Android 11 & 12 have an ABI that the note name is 8 bytes long. Keep it "
"that way for backwards compatibility.");

write32(buf, sizeof(kMemtagAndroidNoteName));
write32(buf + 4, sizeof(uint32_t));
write32(buf + 8, ELF::NT_ANDROID_TYPE_MEMTAG);
memcpy(buf + 12, kMemtagAndroidNoteName, sizeof(kMemtagAndroidNoteName));
buf += 12 + sizeof(kMemtagAndroidNoteName);
buf += 12 + alignTo(sizeof(kMemtagAndroidNoteName), 4);

uint32_t value = 0;
value |= config->androidMemtagMode;
Expand All @@ -3859,7 +3865,7 @@ void MemtagAndroidNote::writeTo(uint8_t *buf) {

size_t MemtagAndroidNote::getSize() const {
return sizeof(llvm::ELF::Elf64_Nhdr) +
/*namesz=*/sizeof(kMemtagAndroidNoteName) +
/*namesz=*/alignTo(sizeof(kMemtagAndroidNoteName), 4) +
/*descsz=*/sizeof(uint32_t);
}

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70 changes: 37 additions & 33 deletions lld/test/ELF/aarch64-memtag-android-abi.s
View file
Expand Up @@ -6,56 +6,60 @@
## can be run on these versions of Android.

# RUN: llvm-mc --filetype=obj -triple=aarch64-none-linux-android %s -o %t.o
# RUN: ld.lld --android-memtag-mode=async --android-memtag-heap %t.o -o %t
# RUN: llvm-readelf -n %t | FileCheck %s --check-prefixes=NOTE,HEAP,NOSTACK,ASYNC
# RUN: ld.lld -shared --android-memtag-mode=async --android-memtag-heap %t.o -o %t
# RUN: llvm-readelf --memtag %t | FileCheck %s --check-prefixes=CHECK,HEAP,NOSTACK,ASYNC

# RUN: ld.lld --android-memtag-mode=sync --android-memtag-heap %t.o -o %t
# RUN: llvm-readelf -n %t | FileCheck %s --check-prefixes=NOTE,HEAP,NOSTACK,SYNC
# RUN: ld.lld -shared --android-memtag-mode=sync --android-memtag-heap %t.o -o %t
# RUN: llvm-readelf --memtag %t | FileCheck %s --check-prefixes=CHECK,HEAP,NOSTACK,SYNC

# RUN: ld.lld --android-memtag-mode=async --android-memtag-stack %t.o -o %t
# RUN: llvm-readelf -n %t | FileCheck %s --check-prefixes=NOTE,NOHEAP,STACK,ASYNC
# RUN: ld.lld -shared --android-memtag-mode=async --android-memtag-stack %t.o -o %t
# RUN: llvm-readelf --memtag %t | FileCheck %s --check-prefixes=CHECK,NOHEAP,STACK,ASYNC

# RUN: ld.lld --android-memtag-mode=sync --android-memtag-stack %t.o -o %t
# RUN: llvm-readelf -n %t | FileCheck %s --check-prefixes=NOTE,NOHEAP,STACK,SYNC
# RUN: ld.lld -shared --android-memtag-mode=sync --android-memtag-stack %t.o -o %t
# RUN: llvm-readelf --memtag %t | FileCheck %s --check-prefixes=CHECK,NOHEAP,STACK,SYNC

# RUN: ld.lld --android-memtag-mode=async --android-memtag-heap \
# RUN: ld.lld -shared --android-memtag-mode=async --android-memtag-heap \
# RUN: --android-memtag-stack %t.o -o %t
# RUN: llvm-readelf -n %t | FileCheck %s --check-prefixes=NOTE,HEAP,STACK,ASYNC
# RUN: llvm-readelf --memtag %t | FileCheck %s --check-prefixes=CHECK,HEAP,STACK,ASYNC

# RUN: ld.lld --android-memtag-mode=sync --android-memtag-heap \
# RUN: ld.lld -shared --android-memtag-mode=sync --android-memtag-heap \
# RUN: --android-memtag-stack %t.o -o %t
# RUN: llvm-readelf -n %t | FileCheck %s --check-prefixes=NOTE,HEAP,STACK,SYNC
# RUN: llvm-readelf --memtag %t | FileCheck %s --check-prefixes=CHECK,HEAP,STACK,SYNC

# RUN: ld.lld --android-memtag-heap %t.o -o %t
# RUN: llvm-readelf -n %t | FileCheck %s --check-prefixes=NOTE,HEAP,NOSTACK,SYNC
# RUN: ld.lld -shared --android-memtag-heap %t.o -o %t 2>&1 | \
# RUN: FileCheck %s --check-prefixes=MISSING-MODE
# RUN: ld.lld -shared --android-memtag-stack %t.o -o %t 2>&1 | \
# RUN: FileCheck %s --check-prefixes=MISSING-MODE
# RUN: ld.lld -shared --android-memtag-heap --android-memtag-stack %t.o -o %t 2>&1 | \
# RUN: FileCheck %s --check-prefixes=MISSING-MODE
# MISSING-MODE: warning: --android-memtag-mode is unspecified, leaving
# MISSING-MODE: --android-memtag-{{(heap|stack)}} a no-op

# RUN: ld.lld --android-memtag-stack %t.o -o %t
# RUN: llvm-readelf -n %t | FileCheck %s --check-prefixes=NOTE,NOHEAP,STACK,SYNC
# CHECK: Memtag Dynamic Entries
# SYNC: AARCH64_MEMTAG_MODE: Synchronous (0)
# ASYNC: AARCH64_MEMTAG_MODE: Asynchronous (1)
# HEAP: AARCH64_MEMTAG_HEAP: Enabled (1)
# NOHEAP: AARCH64_MEMTAG_HEAP: Disabled (0)
# STACK: AARCH64_MEMTAG_STACK: Enabled (1)
# NOSTACK: AARCH64_MEMTAG_STACK: Disabled (0)

# RUN: ld.lld --android-memtag-heap --android-memtag-stack %t.o -o %t
# RUN: llvm-readelf -n %t | FileCheck %s --check-prefixes=NOTE,HEAP,STACK,SYNC

# NOTE: .note.android.memtag
# NOTE-NEXT: Owner
# NOTE-NEXT: Android 0x00000004 NT_ANDROID_TYPE_MEMTAG (Android memory tagging
# NOTE-SAME: information)
# ASYNC-NEXT: Tagging Mode: ASYNC
# SYNC-NEXT: Tagging Mode: SYNC
# HEAP-NEXT: Heap: Enabled
# CHECK: Memtag Android Note
# ASYNC-NEXT: Tagging Mode: ASYNC
# SYNC-NEXT: Tagging Mode: SYNC
# HEAP-NEXT: Heap: Enabled
# NOHEAP-NEXT: Heap: Disabled
## As of Android 12, stack MTE is unimplemented. However, we pre-emptively emit
## a bit that signifies to the dynamic loader to map the primary and thread
## stacks as PROT_MTE, in preparation for the bionic support.
# STACK-NEXT: Stack: Enabled
# NOSTACK-NEXT: Stack: Disabled

# RUN: not ld.lld --android-memtag-mode=asymm --android-memtag-heap 2>&1 | \
# RUN: not ld.lld -shared --android-memtag-mode=asymm --android-memtag-heap 2>&1 | \
# RUN: FileCheck %s --check-prefix=BAD-MODE
# BAD-MODE: unknown --android-memtag-mode value: "asymm", should be one of {async, sync, none}
# BAD-MODE: error: unknown --android-memtag-mode value: "asymm", should be one of
# BAD-MODE: {async, sync, none}

# RUN: not ld.lld --android-memtag-mode=async 2>&1 | \
# RUN: not ld.lld -shared --android-memtag-mode=async 2>&1 | \
# RUN: FileCheck %s --check-prefix=MISSING-STACK-OR-HEAP
# MISSING-STACK-OR-HEAP: when using --android-memtag-mode, at least one of --android-memtag-heap or --android-memtag-stack is required
# MISSING-STACK-OR-HEAP: error: when using --android-memtag-mode, at least one of
# MISSING-STACK-OR-HEAP: --android-memtag-heap or --android-memtag-stack is required

.globl _start
_start:
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