[LLD] Set alignment as part of Characteristics in TLS table.
Fixes https://bugs.llvm.org/show_bug.cgi?id=46473
LLD wasn't previously specifying any specific alignment in the TLS table's Characteristics field so the loader would just assume the default value (16 bytes). This works most of the time except if you have thread locals that want specific higher alignments (e.g. 32 as in the bug) *even* if they specify an alignment on the thread local. This change updates LLD to take the max alignment from tls section.
Reviewed By: rnk
Differential Revision: https://reviews.llvm.org/D88637
diff --git a/lld/COFF/Writer.cpp b/lld/COFF/Writer.cpp
index 0188f09..c7d4de7 100644
--- a/lld/COFF/Writer.cpp
+++ b/lld/COFF/Writer.cpp
@@ -234,6 +234,7 @@
void addSyntheticIdata();
void fixPartialSectionChars(StringRef name, uint32_t chars);
bool fixGnuImportChunks();
+ void fixTlsAlignment();
PartialSection *createPartialSection(StringRef name, uint32_t outChars);
PartialSection *findPartialSection(StringRef name, uint32_t outChars);
@@ -260,6 +261,7 @@
DelayLoadContents delayIdata;
EdataContents edata;
bool setNoSEHCharacteristic = false;
+ uint32_t tlsAlignment = 0;
DebugDirectoryChunk *debugDirectory = nullptr;
std::vector<std::pair<COFF::DebugType, Chunk *>> debugRecords;
@@ -628,6 +630,11 @@
writeSections();
sortExceptionTable();
+ // Fix up the alignment in the TLS Directory's characteristic field,
+ // if a specific alignment value is needed
+ if (tlsAlignment)
+ fixTlsAlignment();
+
t1.stop();
if (!config->pdbPath.empty() && config->debug) {
@@ -848,6 +855,10 @@
StringRef name = c->getSectionName();
if (shouldStripSectionSuffix(sc, name))
name = name.split('$').first;
+
+ if (name.startswith(".tls"))
+ tlsAlignment = std::max(tlsAlignment, c->getAlignment());
+
PartialSection *pSec = createPartialSection(name,
c->getOutputCharacteristics());
pSec->chunks.push_back(c);
@@ -1993,3 +2004,33 @@
return it->second;
return nullptr;
}
+
+void Writer::fixTlsAlignment() {
+ Defined *tlsSym =
+ dyn_cast_or_null<Defined>(symtab->findUnderscore("_tls_used"));
+ if (!tlsSym)
+ return;
+
+ OutputSection *sec = tlsSym->getChunk()->getOutputSection();
+ assert(sec && tlsSym->getRVA() >= sec->getRVA() &&
+ "no output section for _tls_used");
+
+ uint8_t *secBuf = buffer->getBufferStart() + sec->getFileOff();
+ uint64_t tlsOffset = tlsSym->getRVA() - sec->getRVA();
+ uint64_t directorySize = config->is64()
+ ? sizeof(object::coff_tls_directory64)
+ : sizeof(object::coff_tls_directory32);
+
+ if (tlsOffset + directorySize > sec->getRawSize())
+ fatal("_tls_used sym is malformed");
+
+ if (config->is64()) {
+ object::coff_tls_directory64 *tlsDir =
+ reinterpret_cast<object::coff_tls_directory64 *>(&secBuf[tlsOffset]);
+ tlsDir->setAlignment(tlsAlignment);
+ } else {
+ object::coff_tls_directory32 *tlsDir =
+ reinterpret_cast<object::coff_tls_directory32 *>(&secBuf[tlsOffset]);
+ tlsDir->setAlignment(tlsAlignment);
+ }
+}
diff --git a/lld/test/COFF/tls-alignment-32.ll b/lld/test/COFF/tls-alignment-32.ll
index fe8a3e0..0f12498 100644
--- a/lld/test/COFF/tls-alignment-32.ll
+++ b/lld/test/COFF/tls-alignment-32.ll
@@ -11,7 +11,8 @@
; RUN: llvm-readobj --coff-tls-directory %t.exe | FileCheck %s
; CHECK: TLSDirectory {
-; CHECK: Characteristics [ (0x0)
+; CHECK: Characteristics [ (0x600000)
+; CHECK-NEXT: IMAGE_SCN_ALIGN_32BYTES (0x600000)
target triple = "i686-pc-windows-msvc"
diff --git a/lld/test/COFF/tls-alignment-64.ll b/lld/test/COFF/tls-alignment-64.ll
index 495678d..4c5c691 100644
--- a/lld/test/COFF/tls-alignment-64.ll
+++ b/lld/test/COFF/tls-alignment-64.ll
@@ -11,7 +11,8 @@
; RUN: llvm-readobj --coff-tls-directory %t.exe | FileCheck %s
; CHECK: TLSDirectory {
-; CHECK: Characteristics [ (0x0)
+; CHECK: Characteristics [ (0x700000)
+; CHECK-NEXT: IMAGE_SCN_ALIGN_64BYTES (0x700000)
target triple = "x86_64-pc-windows-msvc"
diff --git a/llvm/include/llvm/Object/COFF.h b/llvm/include/llvm/Object/COFF.h
index 505aab8..e7cf1b5 100644
--- a/llvm/include/llvm/Object/COFF.h
+++ b/llvm/include/llvm/Object/COFF.h
@@ -576,11 +576,22 @@
uint32_t getAlignment() const {
// Bit [20:24] contains section alignment.
- uint32_t Shift = (Characteristics & 0x00F00000) >> 20;
+ uint32_t Shift = (Characteristics & COFF::IMAGE_SCN_ALIGN_MASK) >> 20;
if (Shift > 0)
return 1U << (Shift - 1);
return 0;
}
+
+ void setAlignment(uint32_t Align) {
+ uint32_t AlignBits = 0;
+ if (Align) {
+ assert(llvm::isPowerOf2_32(Align) && "alignment is not a power of 2");
+ assert(llvm::Log2_32(Align) <= 13 && "alignment requested is too large");
+ AlignBits = (llvm::Log2_32(Align) + 1) << 20;
+ }
+ Characteristics =
+ (Characteristics & ~COFF::IMAGE_SCN_ALIGN_MASK) | AlignBits;
+ }
};
using coff_tls_directory32 = coff_tls_directory<support::little32_t>;
