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[LLD] Avoid empty .eh_frame sections
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Authored by kettenis on Apr 23 2017, 6:50 AM.

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Reviewers

ruiu
• rafael

Summary

Since D30335: [LLD] Add terminator to .eh_frame sections got reverted, here is a new attempt to address the issue that prompted me to look into the unterminated .eh_frame section issue. This is that strip on OpenBSD does not correctly handle an empty .eh_frame section and produces broken binaries in that case. Currently lld creates such an empty .eh_frame section, despite the fact that the OpenBSD crtend.o explicitly inserts a terminator. The Linux LSB "standard":

https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html#EHFRAME

explicitly says that

The .eh_frame section shall contain 1 or more Call Frame Information (CFI) records.

This diff includes a test that specifically tests the issue I'm seeing on OpenBSD.

Diff Detail

Event Timeline

kettenis created this revision.Apr 23 2017, 6:50 AM

LGTM. I think this is fine, but I'll give Rafael a chance to take a look. Please wait for a few days before submitting.

lld/ELF/SyntheticSections.cpp
548–551	this->Size = (Off == 0) ? 4 : Off;

This revision is now accepted and ready to land.Apr 24 2017, 10:15 AM

Committed r301931

Revision Contents

Path

Size

lld/

ELF/

SyntheticSections.cpp

7 lines

test/

ELF/

Inputs/

eh-frame-end.s

2 lines

eh-frame-begin-end.s

17 lines

Diff 96305

lld/ELF/SyntheticSections.cpp

Show First 20 Lines • Show All 535 Lines • ▼ Show 20 Lines	for (CieRecord *Cie : Cies) {
Cie->Piece->OutputOff = Off;		Cie->Piece->OutputOff = Off;
Off += alignTo(Cie->Piece->size(), Config->Wordsize);		Off += alignTo(Cie->Piece->size(), Config->Wordsize);

for (EhSectionPiece *Fde : Cie->FdePieces) {		for (EhSectionPiece *Fde : Cie->FdePieces) {
Fde->OutputOff = Off;		Fde->OutputOff = Off;
Off += alignTo(Fde->size(), Config->Wordsize);		Off += alignTo(Fde->size(), Config->Wordsize);
}		}
}		}

		// The LSB standard does not allow a .eh_frame section with zero
		// Call Frame Information records. Therefore add a CIE record length
		// 0 as a terminator if this .eh_frame section is empty.
		if (Off == 0)
		Off = 4;

this->Size = Off;		this->Size = Off;
		ruiuUnsubmitted Not Done Reply Inline Actions this->Size = (Off == 0) ? 4 : Off; ruiu: this->Size = (Off == 0) ? 4 : Off;
}		}

template <class ELFT> static uint64_t readFdeAddr(uint8_t *Buf, int Size) {		template <class ELFT> static uint64_t readFdeAddr(uint8_t *Buf, int Size) {
const endianness E = ELFT::TargetEndianness;		const endianness E = ELFT::TargetEndianness;
switch (Size) {		switch (Size) {
case DW_EH_PE_udata2:		case DW_EH_PE_udata2:
return read16<E>(Buf);		return read16<E>(Buf);
case DW_EH_PE_udata4:		case DW_EH_PE_udata4:
▲ Show 20 Lines • Show All 1,795 Lines • Show Last 20 Lines

lld/test/ELF/Inputs/eh-frame-end.s

				.section ".eh_frame", "a", @progbits
				.long 0

lld/test/ELF/eh-frame-begin-end.s

				// REQUIRES: x86
				// RUN: llvm-mc -filetype=obj -triple=amd64-unknown-openbsd %s -o %t.o
				// RUN: llvm-mc -filetype=obj -triple=amd64-unknown-openbsd %p/Inputs/eh-frame-end.s -o %t2.o
				// RUN: ld.lld %t.o %t2.o -o %t
				// RUN: llvm-readobj -sections %t \| FileCheck %s

				// CHECK: Name: .eh_frame
				// CHECK-NEXT: Type: SHT_PROGBITS
				// CHECK-NEXT: Flags [
				// CHECK-NEXT: SHF_ALLOC
				// CHECK-NEXT: ]
				// CHECK-NEXT: Address: 0x200120
				// CHECK-NEXT: Offset: 0x120
				// CHECK-NEXT: Size: 4

				.section ".eh_frame", "a", @progbits
				__EH_FRAME_BEGIN__: