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[lld][COFF] Fill only gaps in code sections. #72138

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Merged
merged 1 commit into from
Nov 14, 2023
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[lld][COFF] Fill only gaps in code sections. #72138

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16 changes: 13 additions & 3 deletions lld/COFF/Writer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2019,10 +2019,20 @@ void Writer::writeSections() {
uint8_t *secBuf = buf + sec->getFileOff();
// Fill gaps between functions in .text with INT3 instructions
// instead of leaving as NUL bytes (which can be interpreted as
// ADD instructions).
// ADD instructions). Only fill the gaps between chunks. Most
// chunks overwrite it anyway, but uninitialized data chunks
// merged into a code section don't.
if ((sec->header.Characteristics & IMAGE_SCN_CNT_CODE) &&
(ctx.config.machine == AMD64 || ctx.config.machine == I386))
memset(secBuf, 0xCC, sec->getRawSize());
(ctx.config.machine == AMD64 || ctx.config.machine == I386)) {
uint32_t prevEnd = 0;
for (Chunk *c : sec->chunks) {
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I think it'd be nice to leave a comment here, saying what this does. E.g. something like this? "Only fill the gaps between chunks. Most chunks overwrite it anyway, but uninitialized data chunks merged into a code section don't."

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Done, thanks!

uint32_t off = c->getRVA() - sec->getRVA();
memset(secBuf + prevEnd, 0xCC, off - prevEnd);
prevEnd = off + c->getSize();
}
memset(secBuf + prevEnd, 0xCC, sec->getRawSize() - prevEnd);
}

parallelForEach(sec->chunks, [&](Chunk *c) {
c->writeTo(secBuf + c->getRVA() - sec->getRVA());
});
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146 changes: 146 additions & 0 deletions lld/test/COFF/code-merge.s
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@@ -0,0 +1,146 @@
# REQUIRES: x86

# Test merging code sections with data sections.

# RUN: llvm-mc -triple x86_64-windows-msvc %s -filetype=obj -o %t.obj
# RUN: lld-link -machine:amd64 -dll -noentry -out:%t.dll %t.obj -merge:.testx=.testd -merge:.testx2=.testbss -merge:.testd2=.testx3 -merge:.testbss2=.testx4

# RUN: llvm-readobj --sections %t.dll | FileCheck %s
# CHECK: Sections [
# CHECK-NEXT: Section {
# CHECK-NEXT: Number: 1
# CHECK-NEXT: Name: .testbss (2E 74 65 73 74 62 73 73)
# CHECK-NEXT: VirtualSize: 0x18
# CHECK-NEXT: VirtualAddress: 0x1000
# CHECK-NEXT: RawDataSize: 512
# CHECK-NEXT: PointerToRawData: 0x400
# CHECK-NEXT: PointerToRelocations: 0x0
# CHECK-NEXT: PointerToLineNumbers: 0x0
# CHECK-NEXT: RelocationCount: 0
# CHECK-NEXT: LineNumberCount: 0
# CHECK-NEXT: Characteristics [ (0xC0000080)
# CHECK-NEXT: IMAGE_SCN_CNT_UNINITIALIZED_DATA (0x80)
# CHECK-NEXT: IMAGE_SCN_MEM_READ (0x40000000)
# CHECK-NEXT: IMAGE_SCN_MEM_WRITE (0x80000000)
# CHECK-NEXT: ]
# CHECK-NEXT: }
# CHECK-NEXT: Section {
# CHECK-NEXT: Number: 2
# CHECK-NEXT: Name: .testd (2E 74 65 73 74 64 00 00)
# CHECK-NEXT: VirtualSize: 0x18
# CHECK-NEXT: VirtualAddress: 0x2000
# CHECK-NEXT: RawDataSize: 512
# CHECK-NEXT: PointerToRawData: 0x600
# CHECK-NEXT: PointerToRelocations: 0x0
# CHECK-NEXT: PointerToLineNumbers: 0x0
# CHECK-NEXT: RelocationCount: 0
# CHECK-NEXT: LineNumberCount: 0
# CHECK-NEXT: Characteristics [ (0x40000040)
# CHECK-NEXT: IMAGE_SCN_CNT_INITIALIZED_DATA (0x40)
# CHECK-NEXT: IMAGE_SCN_MEM_READ (0x40000000)
# CHECK-NEXT: ]
# CHECK-NEXT: }
# CHECK-NEXT: Section {
# CHECK-NEXT: Number: 3
# CHECK-NEXT: Name: .testx3 (2E 74 65 73 74 78 33 00)
# CHECK-NEXT: VirtualSize: 0x12
# CHECK-NEXT: VirtualAddress: 0x3000
# CHECK-NEXT: RawDataSize: 512
# CHECK-NEXT: PointerToRawData: 0x800
# CHECK-NEXT: PointerToRelocations: 0x0
# CHECK-NEXT: PointerToLineNumbers: 0x0
# CHECK-NEXT: RelocationCount: 0
# CHECK-NEXT: LineNumberCount: 0
# CHECK-NEXT: Characteristics [ (0x60000020)
# CHECK-NEXT: IMAGE_SCN_CNT_CODE (0x20)
# CHECK-NEXT: IMAGE_SCN_MEM_EXECUTE (0x20000000)
# CHECK-NEXT: IMAGE_SCN_MEM_READ (0x40000000)
# CHECK-NEXT: ]
# CHECK-NEXT: }
# CHECK-NEXT: Section {
# CHECK-NEXT: Number: 4
# CHECK-NEXT: Name: .testx4 (2E 74 65 73 74 78 34 00)
# CHECK-NEXT: VirtualSize: 0x14
# CHECK-NEXT: VirtualAddress: 0x4000
# CHECK-NEXT: RawDataSize: 512
# CHECK-NEXT: PointerToRawData: 0xA00
# CHECK-NEXT: PointerToRelocations: 0x0
# CHECK-NEXT: PointerToLineNumbers: 0x0
# CHECK-NEXT: RelocationCount: 0
# CHECK-NEXT: LineNumberCount: 0
# CHECK-NEXT: Characteristics [ (0x60000020)
# CHECK-NEXT: IMAGE_SCN_CNT_CODE (0x20)
# CHECK-NEXT: IMAGE_SCN_MEM_EXECUTE (0x20000000)
# CHECK-NEXT: IMAGE_SCN_MEM_READ (0x40000000)
# CHECK-NEXT: ]
# CHECK-NEXT: }
# CHECK-NEXT: ]

# RUN: llvm-objdump -d %t.dll | FileCheck -check-prefix=DISASM %s
# DISASM: Disassembly of section .testx3:
# DISASM-EMPTY:
# DISASM-NEXT: 0000000180003000 <.testx3>:
# DISASM-NEXT: 180003000: 48 c7 c0 03 00 00 00 movq $0x3, %rax
# DISASM-NEXT: 180003007: c3 retq
# DISASM-NEXT: 180003008: cc int3
# DISASM-NEXT: 180003009: cc int3
# DISASM-NEXT: 18000300a: cc int3
# DISASM-NEXT: 18000300b: cc int3
# DISASM-NEXT: 18000300c: cc int3
# DISASM-NEXT: 18000300d: cc int3
# DISASM-NEXT: 18000300e: cc int3
# DISASM-NEXT: 18000300f: cc int3
# DISASM-NEXT: 180003010: 02 00 addb (%rax), %al
# DISASM-EMPTY:
# DISASM-NEXT: Disassembly of section .testx4:
# DISASM-EMPTY:
# DISASM-NEXT: 0000000180004000 <.testx4>:
# DISASM-NEXT: 180004000: 48 c7 c0 04 00 00 00 movq $0x4, %rax
# DISASM-NEXT: 180004007: c3 retq
# DISASM-NEXT: 180004008: cc int3
# DISASM-NEXT: 180004009: cc int3
# DISASM-NEXT: 18000400a: cc int3
# DISASM-NEXT: 18000400b: cc int3
# DISASM-NEXT: 18000400c: cc int3
# DISASM-NEXT: 18000400d: cc int3
# DISASM-NEXT: 18000400e: cc int3
# DISASM-NEXT: 18000400f: cc int3
# DISASM-NEXT: 180004010: 00 00 addb %al, (%rax)
# DISASM-NEXT: 180004012: 00 00 addb %al, (%rax)


.section .testx, "xr"
.p2align 4
movq $1, %rax
retq

.section .testx2, "xr"
.p2align 4
movq $2, %rax
retq

.section .testd, "dr"
.p2align 4
.word 1

.section .testbss, "b"
.p2align 4
.skip 4

.section .testx3, "xr"
.p2align 4
movq $3, %rax
retq

.section .testx4, "xr"
.p2align 4
movq $4, %rax
retq

.section .testd2, "dr"
.p2align 4
.word 2

.section .testbss2, "b"
.p2align 4
.skip 4