[lld] r260465 - Don't include NOBITS TLS in PT_LOAD.
Rafael Espindola via llvm-commits
llvm-commits at lists.llvm.org
Wed Feb 10 15:29:39 PST 2016
Author: rafael
Date: Wed Feb 10 17:29:38 2016
New Revision: 260465
URL: http://llvm.org/viewvc/llvm-project?rev=260465&view=rev
Log:
Don't include NOBITS TLS in PT_LOAD.
They don't count for the memory or file size, so this is mostly just a
simplification.
The only noticeable difference should be fewer empty program headers.
Added:
lld/trunk/test/ELF/avoid-empty-program-headers.s
Modified:
lld/trunk/ELF/Writer.cpp
Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=260465&r1=260464&r2=260465&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Wed Feb 10 17:29:38 2016
@@ -1184,8 +1184,16 @@ void Writer<ELFT>::addStartStopSymbols(O
Symtab.addSynthetic(Stop, *Sec, Sec->getSize());
}
-template <class ELFT> static bool needsPhdr(OutputSectionBase<ELFT> *Sec) {
- return Sec->getFlags() & SHF_ALLOC;
+template <class ELFT> static bool needsPtLoad(OutputSectionBase<ELFT> *Sec) {
+ if (!(Sec->getFlags() & SHF_ALLOC))
+ return false;
+
+ // Don't allocate VA space for TLS NOBITS sections. The PT_TLS PHDR is
+ // responsible for allocating space for them, not the PT_LOAD that
+ // contains the TLS initialization image.
+ if (Sec->getFlags() & SHF_TLS && Sec->getType() == SHT_NOBITS)
+ return false;
+ return true;
}
static uint32_t toPhdrFlags(uint64_t Flags) {
@@ -1241,9 +1249,18 @@ template <class ELFT> void Writer<ELFT>:
Phdr TlsHdr(PT_TLS, PF_R);
Phdr RelRo(PT_GNU_RELRO, PF_R);
for (OutputSectionBase<ELFT> *Sec : OutputSections) {
- if (!needsPhdr<ELFT>(Sec))
+ if (!(Sec->getFlags() & SHF_ALLOC))
break;
+ // If we meet TLS section then we create TLS header
+ // and put all TLS sections inside for futher use when
+ // assign addresses.
+ if (Sec->getFlags() & SHF_TLS)
+ AddSec(TlsHdr, Sec);
+
+ if (!needsPtLoad<ELFT>(Sec))
+ continue;
+
// If flags changed then we want new load segment.
uintX_t NewFlags = toPhdrFlags(Sec->getFlags());
if (Flags != NewFlags) {
@@ -1252,14 +1269,6 @@ template <class ELFT> void Writer<ELFT>:
Load = AddHdr(LoadType, NewFlags);
Flags = NewFlags;
}
- // If we meet TLS section then we create TLS header
- // and put all TLS sections inside for futher use when
- // assign addresses.
- if (Sec->getFlags() & SHF_TLS) {
- AddSec(TlsHdr, Sec);
- if (Sec->getType() == SHT_NOBITS)
- continue;
- }
AddSec(*Load, Sec);
@@ -1307,18 +1316,15 @@ template <class ELFT> void Writer<ELFT>:
SmallPtrSet<OutputSectionBase<ELFT> *, 4> PageAlign;
for (const Phdr &P : Phdrs) {
if (P.H.p_type == PT_GNU_RELRO) {
- // Find the first section after PT_GNU_RELRO. If it is in a PT_LOAD
- // and is not tls, we have to align it to a page. We don't have to
- // align tls since TLS NOBITS takes no space.
+ // Find the first section after PT_GNU_RELRO. If it is in a PT_LOAD we
+ // have to align it to a page.
auto I = std::find(OutputSections.begin(), OutputSections.end(), P.Last);
++I;
- if (I != OutputSections.end() && needsPhdr(*I) &&
- !((*I)->getFlags() & SHF_TLS))
+ if (I != OutputSections.end() && needsPtLoad(*I))
PageAlign.insert(*I);
}
- // FIXME: why create empty PT_LOAD?
- if (P.H.p_type == PT_LOAD && P.First)
+ if (P.H.p_type == PT_LOAD)
PageAlign.insert(P.First);
}
@@ -1337,21 +1343,15 @@ template <class ELFT> void Writer<ELFT>:
FileOff += Sec->getSize();
// We only assign VAs to allocated sections.
- if (needsPhdr<ELFT>(Sec)) {
- // Don't allocate VA space for TLS NOBITS sections. The PT_TLS PHDR is
- // responsible for allocating space for them, not the PT_LOAD that
- // contains the TLS initialization image.
- bool IsTls = Sec->getFlags() & SHF_TLS;
- if (IsTls && Sec->getType() == SHT_NOBITS) {
- uintX_t TVA = VA + ThreadBssOffset;
- TVA = alignTo(TVA, Align);
- Sec->setVA(TVA);
- ThreadBssOffset = TVA - VA + Sec->getSize();
- } else {
- VA = alignTo(VA, Align);
- Sec->setVA(VA);
- VA += Sec->getSize();
- }
+ if (needsPtLoad<ELFT>(Sec)) {
+ VA = alignTo(VA, Align);
+ Sec->setVA(VA);
+ VA += Sec->getSize();
+ } else if (Sec->getFlags() & SHF_TLS && Sec->getType() == SHT_NOBITS) {
+ uintX_t TVA = VA + ThreadBssOffset;
+ TVA = alignTo(TVA, Align);
+ Sec->setVA(TVA);
+ ThreadBssOffset = TVA - VA + Sec->getSize();
}
}
Added: lld/trunk/test/ELF/avoid-empty-program-headers.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/avoid-empty-program-headers.s?rev=260465&view=auto
==============================================================================
--- lld/trunk/test/ELF/avoid-empty-program-headers.s (added)
+++ lld/trunk/test/ELF/avoid-empty-program-headers.s Wed Feb 10 17:29:38 2016
@@ -0,0 +1,78 @@
+// REQUIRES: x86
+// RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+// RUN: ld.lld %t -o %tout
+// RUN: llvm-readobj -program-headers %tout | FileCheck %s
+
+.global _start
+_start:
+ retq
+
+.section .tbss,"awT", at nobits
+ .zero 4
+// FIXME: Test that we don't create unecessary empty PT_LOAD and PT_GNU_RELRO
+// for the .tbss section.
+
+// CHECK: ProgramHeaders [
+// CHECK-NEXT: ProgramHeader {
+// CHECK-NEXT: Type: PT_PHDR (0x6)
+// CHECK-NEXT: Offset: 0x40
+// CHECK-NEXT: VirtualAddress: 0x10040
+// CHECK-NEXT: PhysicalAddress: 0x10040
+// CHECK-NEXT: FileSize: 280
+// CHECK-NEXT: MemSize: 280
+// CHECK-NEXT: Flags [ (0x4)
+// CHECK-NEXT: PF_R (0x4)
+// CHECK-NEXT: ]
+// CHECK-NEXT: Alignment: 8
+// CHECK-NEXT: }
+// CHECK-NEXT: ProgramHeader {
+// CHECK-NEXT: Type: PT_LOAD (0x1)
+// CHECK-NEXT: Offset: 0x0
+// CHECK-NEXT: VirtualAddress: 0x10000
+// CHECK-NEXT: PhysicalAddress: 0x10000
+// CHECK-NEXT: FileSize: 344
+// CHECK-NEXT: MemSize: 344
+// CHECK-NEXT: Flags [ (0x4)
+// CHECK-NEXT: PF_R (0x4)
+// CHECK-NEXT: ]
+// CHECK-NEXT: Alignment: 4096
+// CHECK-NEXT: }
+// CHECK-NEXT: ProgramHeader {
+// CHECK-NEXT: Type: PT_LOAD (0x1)
+// CHECK-NEXT: Offset: 0x1000
+// CHECK-NEXT: VirtualAddress: 0x11000
+// CHECK-NEXT: PhysicalAddress: 0x11000
+// CHECK-NEXT: FileSize: 1
+// CHECK-NEXT: MemSize: 1
+// CHECK-NEXT: Flags [ (0x5)
+// CHECK-NEXT: PF_R (0x4)
+// CHECK-NEXT: PF_X (0x1)
+// CHECK-NEXT: ]
+// CHECK-NEXT: Alignment: 4096
+// CHECK-NEXT: }
+// CHECK-NEXT: ProgramHeader {
+// CHECK-NEXT: Type: PT_TLS (0x7)
+// CHECK-NEXT: Offset: 0x1001
+// CHECK-NEXT: VirtualAddress: 0x11001
+// CHECK-NEXT: PhysicalAddress: 0x11001
+// CHECK-NEXT: FileSize: 0
+// CHECK-NEXT: MemSize: 4
+// CHECK-NEXT: Flags [ (0x4)
+// CHECK-NEXT: PF_R (0x4)
+// CHECK-NEXT: ]
+// CHECK-NEXT: Alignment: 1
+// CHECK-NEXT: }
+// CHECK-NEXT: ProgramHeader {
+// CHECK-NEXT: Type: PT_GNU_STACK (0x6474E551)
+// CHECK-NEXT: Offset: 0x0
+// CHECK-NEXT: VirtualAddress: 0x0
+// CHECK-NEXT: PhysicalAddress: 0x0
+// CHECK-NEXT: FileSize: 0
+// CHECK-NEXT: MemSize: 0
+// CHECK-NEXT: Flags [ (0x6)
+// CHECK-NEXT: PF_R (0x4)
+// CHECK-NEXT: PF_W (0x2)
+// CHECK-NEXT: ]
+// CHECK-NEXT: Alignment: 0
+// CHECK-NEXT: }
+// CHECK-NEXT: ]
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