[PATCH] D12718: [elf2] Assign output sections to PHDRs.
Rafael Espíndola via llvm-commits
llvm-commits at lists.llvm.org
Wed Sep 9 08:46:10 PDT 2015
rebased patch attached.
On 9 September 2015 at 10:28, Rafael Espíndola
<rafael.espindola at gmail.com> wrote:
> + static const uint64_t BaseAddress = 0x400000;
>
> Any reason to change this in this patch? It can be done in another
> patch if there is any advantage to it, no?
>
> + FileOff = RoundUpToAlignment(FileOff, ELFT::Is64Bits ? 8 : 4);
>
> That is not needed. The file header size is already a multiple of 8 or
> 4. You can assert it if you want.
>
> + for (OutputSectionBase<ELFT::Is64Bits> *Sec : OutputSections)
> + if (outputSectionHasPHDR<ELFT>(Sec)) {
> + FileOff += sizeof(Elf_Phdr_Impl<ELFT>);
>
> Use Elf_Phdr instead of Elf_Phdr_Impl
>
> + ++NumPhdrs;
> + }
>
> Include {} around the for. Alternatively, write it as
>
>
> for (OutputSectionBase<ELFT::Is64Bits> *Sec : OutputSections)
> if (outputSectionHasPHDR<ELFT>(Sec))
> ++NumPhdrs;
>
> FileOff += NumPhdrs * sizeof(Elf_Phdr);
>
> Even better, we can merge the loop with the following one since all
> the program headers should fit in the first page (which is plenty of
> space, specially once we create one per flag combination instead of
> one per output section):
>
> https://github.com/freebsd/freebsd/blob/a8fae65d69bf46d8a4aa6351092235ee691df503/sys/kern/imgact_elf.c#L674
>
>
> + FileSize = RoundUpToAlignment(FileOff, 8);
>
> This can just be
>
> FileSize = FileOff;
>
> no? Why do we have to pad the end of the file?
>
> An attached patch with most of these comments is attached.
>
>
> On 8 September 2015 at 22:06, Michael Spencer <bigcheesegs at gmail.com> wrote:
>> Bigcheese created this revision.
>> Bigcheese added a reviewer: rafael.
>> Bigcheese added a subscriber: llvm-commits.
>>
>> This is a minimal implementation to produce legal output. Future patches will combine multiple compatible PT_LOADs.
>>
>> It uses the term PHDR instead of segment as not all PHDRs represent segments.
>>
>> http://reviews.llvm.org/D12718
>>
>> Files:
>> ELF/Writer.cpp
>> test/elf2/basic.s
>> test/elf2/basic32.s
>> test/elf2/basic32be.s
>> test/elf2/basic64be.s
>> test/elf2/bss.s
>> test/elf2/common.s
>> test/elf2/relocation.s
>> test/elf2/shared.s
>> test/elf2/string-table.s
>> test/elf2/symbols.s
>> test/elf2/visibility.s
>>
-------------- next part --------------
diff --git a/ELF/Writer.cpp b/ELF/Writer.cpp
index 91771b3..7a39b0a 100644
--- a/ELF/Writer.cpp
+++ b/ELF/Writer.cpp
@@ -228,8 +228,9 @@ private:
unsigned getNumSections() const { return OutputSections.size() + 1; }
uintX_t FileSize;
- uintX_t SizeOfHeaders;
+ uintX_t ProgramHeaderOff;
uintX_t SectionHeaderOff;
+ unsigned NumPhdrs;
StringTableSection<ELFT::Is64Bits> StrTabSec;
StringTableSection<ELFT::Is64Bits> DynStrSec;
@@ -556,17 +557,34 @@ template <class ELFT> void Writer<ELFT>::createSections() {
OutputSections[I]->setSectionIndex(I + 1);
}
+template <class ELFT>
+static bool outputSectionHasPHDR(OutputSectionBase<ELFT::Is64Bits> *Sec) {
+ return (Sec->getSize() != 0) && (Sec->getFlags() & SHF_ALLOC);
+}
+
// Visits all sections to assign incremental, non-overlapping RVAs and
// file offsets.
template <class ELFT> void Writer<ELFT>::assignAddresses() {
- SizeOfHeaders = RoundUpToAlignment(sizeof(Elf_Ehdr), PageSize);
uintX_t VA = 0x1000; // The first page is kept unmapped.
- uintX_t FileOff = SizeOfHeaders;
+ uintX_t FileOff = sizeof(Elf_Ehdr);
+
+ // Reserve space for PHDRs.
+ ProgramHeaderOff = FileOff;
+ FileOff = RoundUpToAlignment(FileOff, PageSize);
+ NumPhdrs = 0;
for (OutputSectionBase<ELFT::Is64Bits> *Sec : OutputSections) {
StrTabSec.add(Sec->getName());
Sec->finalize();
+ // Since each output section gets its own PHDR, align each output section to
+ // a page.
+ if (outputSectionHasPHDR<ELFT>(Sec)) {
+ ++NumPhdrs;
+ VA = RoundUpToAlignment(VA, PageSize);
+ FileOff = RoundUpToAlignment(FileOff, PageSize);
+ }
+
uintX_t Align = Sec->getAlign();
uintX_t Size = Sec->getSize();
if (Sec->getFlags() & SHF_ALLOC) {
@@ -578,15 +596,19 @@ template <class ELFT> void Writer<ELFT>::assignAddresses() {
FileOff += RoundUpToAlignment(Size, Align);
}
+ // Add a PHDR for the dynamic table.
+ if (!SymTable.getSymTable().getSharedFiles().empty())
+ ++NumPhdrs;
+
FileOff += OffsetToAlignment(FileOff, ELFT::Is64Bits ? 8 : 4);
// Add space for section headers.
SectionHeaderOff = FileOff;
FileOff += getNumSections() * sizeof(Elf_Shdr);
- FileSize = SizeOfHeaders + RoundUpToAlignment(FileOff - SizeOfHeaders, 8);
+ FileSize = FileOff;
}
-static uint32_t convertSectionFlagsToSegmentFlags(uint64_t Flags) {
+static uint32_t convertSectionFlagsToPHDRFlags(uint64_t Flags) {
uint32_t Ret = PF_R;
if (Flags & SHF_WRITE)
Ret |= PF_W;
@@ -613,42 +635,41 @@ template <class ELFT> void Writer<ELFT>::writeHeader() {
// FIXME: Generalize the segment construction similar to how we create
// output sections.
- unsigned NumSegments = 1;
const SymbolTable &Symtab = SymTable.getSymTable();
- const std::vector<std::unique_ptr<SharedFileBase>> &SharedFiles =
- Symtab.getSharedFiles();
- bool HasDynamicSegment = !SharedFiles.empty();
- if (HasDynamicSegment)
- NumSegments++;
+ bool HasDynamicSegment = !Symtab.getSharedFiles().empty();
EHdr->e_type = ET_EXEC;
auto &FirstObj = cast<ObjectFile<ELFT>>(*Symtab.getFirstELF());
EHdr->e_machine = FirstObj.getEMachine();
EHdr->e_version = EV_CURRENT;
EHdr->e_entry = getSymVA(cast<DefinedRegular<ELFT>>(Symtab.getEntrySym()));
- EHdr->e_phoff = sizeof(Elf_Ehdr);
+ EHdr->e_phoff = ProgramHeaderOff;
EHdr->e_shoff = SectionHeaderOff;
EHdr->e_ehsize = sizeof(Elf_Ehdr);
EHdr->e_phentsize = sizeof(Elf_Phdr);
- EHdr->e_phnum = NumSegments;
+ EHdr->e_phnum = NumPhdrs;
EHdr->e_shentsize = sizeof(Elf_Shdr);
EHdr->e_shnum = getNumSections();
EHdr->e_shstrndx = StrTabSec.getSectionIndex();
auto PHdrs = reinterpret_cast<Elf_Phdr *>(Buf + EHdr->e_phoff);
- PHdrs->p_type = PT_LOAD;
- PHdrs->p_flags = PF_R | PF_X;
- PHdrs->p_offset = 0x0000;
- PHdrs->p_vaddr = 0x1000;
- PHdrs->p_paddr = PHdrs->p_vaddr;
- PHdrs->p_filesz = FileSize;
- PHdrs->p_memsz = FileSize;
- PHdrs->p_align = 0x4000;
+ for (OutputSectionBase<ELFT::Is64Bits> *Sec : OutputSections) {
+ if (!outputSectionHasPHDR<ELFT>(Sec))
+ continue;
+ PHdrs->p_type = PT_LOAD;
+ PHdrs->p_flags = convertSectionFlagsToPHDRFlags(Sec->getFlags());
+ PHdrs->p_offset = Sec->getFileOff();
+ PHdrs->p_vaddr = Sec->getVA();
+ PHdrs->p_paddr = PHdrs->p_vaddr;
+ PHdrs->p_filesz = Sec->getType() == SHT_NOBITS ? 0 : Sec->getSize();
+ PHdrs->p_memsz = Sec->getSize();
+ PHdrs->p_align = PageSize;
+ ++PHdrs;
+ }
if (HasDynamicSegment) {
- PHdrs++;
PHdrs->p_type = PT_DYNAMIC;
- PHdrs->p_flags = convertSectionFlagsToSegmentFlags(DynamicSec.getFlags());
+ PHdrs->p_flags = convertSectionFlagsToPHDRFlags(DynamicSec.getFlags());
PHdrs->p_offset = DynamicSec.getFileOff();
PHdrs->p_vaddr = DynamicSec.getVA();
PHdrs->p_paddr = PHdrs->p_vaddr;
diff --git a/test/elf2/basic.s b/test/elf2/basic.s
index 351f767..004cf7d 100644
--- a/test/elf2/basic.s
+++ b/test/elf2/basic.s
@@ -151,16 +151,16 @@ _start:
# CHECK-NEXT: ProgramHeaders [
# CHECK-NEXT: ProgramHeader {
# CHECK-NEXT: Type: PT_LOAD (0x1)
-# CHECK-NEXT: Offset: 0x0
+# CHECK-NEXT: Offset: 0x1000
# CHECK-NEXT: VirtualAddress: 0x1000
# CHECK-NEXT: PhysicalAddress: 0x1000
-# CHECK-NEXT: FileSize: 4592
-# CHECK-NEXT: MemSize: 4592
+# CHECK-NEXT: FileSize: 16
+# CHECK-NEXT: MemSize: 16
# CHECK-NEXT: Flags [ (0x5)
# CHECK-NEXT: PF_R (0x4)
# CHECK-NEXT: PF_X (0x1)
# CHECK-NEXT: ]
-# CHECK-NEXT: Alignment: 16384
+# CHECK-NEXT: Alignment: 4096
# CHECK-NEXT: }
# CHECK-NEXT: ]
diff --git a/test/elf2/basic32.s b/test/elf2/basic32.s
index 4aace02..7c477ef 100644
--- a/test/elf2/basic32.s
+++ b/test/elf2/basic32.s
@@ -130,15 +130,15 @@ _start:
# CHECK-NEXT: ProgramHeaders [
# CHECK-NEXT: ProgramHeader {
# CHECK-NEXT: Type: PT_LOAD (0x1)
-# CHECK-NEXT: Offset: 0x0
+# CHECK-NEXT: Offset: 0x1000
# CHECK-NEXT: VirtualAddress: 0x1000
# CHECK-NEXT: PhysicalAddress: 0x1000
-# CHECK-NEXT: FileSize: 4424
-# CHECK-NEXT: MemSize: 4424
+# CHECK-NEXT: FileSize: 12
+# CHECK-NEXT: MemSize: 12
# CHECK-NEXT: Flags [ (0x5)
# CHECK-NEXT: PF_R (0x4)
# CHECK-NEXT: PF_X (0x1)
# CHECK-NEXT: ]
-# CHECK-NEXT: Alignment: 16384
+# CHECK-NEXT: Alignment: 4096
# CHECK-NEXT: }
# CHECK-NEXT: ]
diff --git a/test/elf2/basic32be.s b/test/elf2/basic32be.s
index b305ac9..be6d55a 100644
--- a/test/elf2/basic32be.s
+++ b/test/elf2/basic32be.s
@@ -130,15 +130,15 @@ _start:
# CHECK-NEXT: ProgramHeaders [
# CHECK-NEXT: ProgramHeader {
# CHECK-NEXT: Type: PT_LOAD (0x1)
-# CHECK-NEXT: Offset: 0x0
+# CHECK-NEXT: Offset: 0x1000
# CHECK-NEXT: VirtualAddress: 0x1000
# CHECK-NEXT: PhysicalAddress: 0x1000
-# CHECK-NEXT: FileSize: 4424
-# CHECK-NEXT: MemSize: 4424
+# CHECK-NEXT: FileSize: 12
+# CHECK-NEXT: MemSize: 12
# CHECK-NEXT: Flags [ (0x5)
# CHECK-NEXT: PF_R (0x4)
# CHECK-NEXT: PF_X (0x1)
# CHECK-NEXT: ]
-# CHECK-NEXT: Alignment: 16384
+# CHECK-NEXT: Alignment: 4096
# CHECK-NEXT: }
# CHECK-NEXT: ]
diff --git a/test/elf2/basic64be.s b/test/elf2/basic64be.s
index 52f1e9d..1fe6181 100644
--- a/test/elf2/basic64be.s
+++ b/test/elf2/basic64be.s
@@ -28,14 +28,14 @@ _start:
# CHECK-NEXT: Type: Executable (0x2)
# CHECK-NEXT: Machine: EM_PPC64 (0x15)
# CHECK-NEXT: Version: 1
-# CHECK-NEXT: Entry: 0x100C
+# CHECK-NEXT: Entry: 0x2000
# CHECK-NEXT: ProgramHeaderOffset: 0x40
-# CHECK-NEXT: SectionHeaderOffset: 0x1088
+# CHECK-NEXT: SectionHeaderOffset: 0x2078
# CHECK-NEXT: Flags [ (0x0)
# CHECK-NEXT: ]
# CHECK-NEXT: HeaderSize: 64
# CHECK-NEXT: ProgramHeaderEntrySize: 56
-# CHECK-NEXT: ProgramHeaderCount: 1
+# CHECK-NEXT: ProgramHeaderCount: 2
# CHECK-NEXT: SectionHeaderEntrySize: 64
# CHECK-NEXT: SectionHeaderCount: 7
# CHECK-NEXT: StringTableSectionIndex: 6
@@ -111,8 +111,8 @@ _start:
# CHECK-NEXT: SHF_ALLOC (0x2)
# CHECK-NEXT: SHF_WRITE (0x1)
# CHECK-NEXT: ]
-# CHECK-NEXT: Address: 0x100C
-# CHECK-NEXT: Offset: 0x100C
+# CHECK-NEXT: Address: 0x2000
+# CHECK-NEXT: Offset: 0x2000
# CHECK-NEXT: Size: 24
# CHECK-NEXT: Link: 0
# CHECK-NEXT: Info: 0
@@ -126,7 +126,7 @@ _start:
# CHECK-NEXT: Flags [
# CHECK-NEXT: ]
# CHECK-NEXT: Address: 0x0
-# CHECK-NEXT: Offset: 0x1024
+# CHECK-NEXT: Offset: 0x2018
# CHECK-NEXT: Size: 48
# CHECK-NEXT: Link: 6
# CHECK-NEXT: Info: 1
@@ -140,7 +140,7 @@ _start:
# CHECK-NEXT: Flags [ (0x0)
# CHECK-NEXT: ]
# CHECK-NEXT: Address: 0x0
-# CHECK-NEXT: Offset: 0x1054
+# CHECK-NEXT: Offset: 0x2048
# CHECK-NEXT: Size: 46
# CHECK-NEXT: Link: 0
# CHECK-NEXT: Info: 0
@@ -149,17 +149,30 @@ _start:
# CHECK-NEXT: }
# CHECK-NEXT: ]
# CHECK-NEXT: ProgramHeaders [
-# CHECK-NEXT: ProgramHeader {
-# CHECK-NEXT: Type: PT_LOAD (0x1)
-# CHECK-NEXT: Offset: 0x0
-# CHECK-NEXT: VirtualAddress: 0x1000
-# CHECK-NEXT: PhysicalAddress: 0x1000
-# CHECK-NEXT: FileSize: 4680
-# CHECK-NEXT: MemSize: 4680
-# CHECK-NEXT: Flags [ (0x5)
-# CHECK-NEXT: PF_R (0x4)
-# CHECK-NEXT: PF_X (0x1)
-# CHECK-NEXT: ]
-# CHECK-NEXT: Alignment: 16384
-# CHECK-NEXT: }
-# CHECK-NEXT: ]
+# CHECK-NEXT: ProgramHeader {
+# CHECK-NEXT: Type: PT_LOAD (0x1)
+# CHECK-NEXT: Offset: 0x1000
+# CHECK-NEXT: VirtualAddress: 0x1000
+# CHECK-NEXT: PhysicalAddress: 0x1000
+# CHECK-NEXT: FileSize: 12
+# CHECK-NEXT: MemSize: 12
+# 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_LOAD (0x1)
+# CHECK-NEXT: Offset: 0x2000
+# CHECK-NEXT: VirtualAddress: 0x2000
+# CHECK-NEXT: PhysicalAddress: 0x2000
+# CHECK-NEXT: FileSize: 24
+# CHECK-NEXT: MemSize: 24
+# CHECK-NEXT: Flags [ (0x6)
+# CHECK-NEXT: PF_R (0x4)
+# CHECK-NEXT: PF_W (0x2)
+# CHECK-NEXT: ]
+# CHECK-NEXT: Alignment: 4096
+# CHECK-NEXT: }
+# CHECK-NEXT:]
diff --git a/test/elf2/relocation.s b/test/elf2/relocation.s
index 054846e..7c1e920 100644
--- a/test/elf2/relocation.s
+++ b/test/elf2/relocation.s
@@ -26,4 +26,4 @@ bar:
// CHECK: e8 04 00 00 00 callq 4
// Also check that symbols match.
-// CHECK: 0000000000001000 .text 00000000 bar
+// CHECK: 000000000001000 .text 00000000 bar
diff --git a/test/elf2/symbols.s b/test/elf2/symbols.s
index eb8a549..8fb9a0c 100644
--- a/test/elf2/symbols.s
+++ b/test/elf2/symbols.s
@@ -59,8 +59,8 @@ internal:
// CHECK-NEXT: SHF_ALLOC (0x2)
// CHECK-NEXT: SHF_WRITE (0x1)
// CHECK-NEXT: ]
-// CHECK-NEXT: Address: 0x1004
-// CHECK-NEXT: Offset: 0x1004
+// CHECK-NEXT: Address: 0x2000
+// CHECK-NEXT: Offset: 0x2000
// CHECK-NEXT: Size: 4
// CHECK: Name: foobar
@@ -68,7 +68,7 @@ internal:
// CHECK-NEXT: Flags [
// CHECK-NEXT: SHF_ALLOC
// CHECK-NEXT: ]
-// CHECK-NEXT: Address: 0x1008
+// CHECK-NEXT: Address: 0x3000
// CHECK: Symbols [
// CHECK-NEXT: Symbol {
@@ -118,7 +118,7 @@ internal:
// CHECK-NEXT: }
// CHECK-NEXT: Symbol {
// CHECK-NEXT: Name: common (34)
-// CHECK-NEXT: Value: 0x1004
+// CHECK-NEXT: Value: 0x2000
// CHECK-NEXT: Size: 4
// CHECK-NEXT: Binding: Global (0x1)
// CHECK-NEXT: Type: Object (0x1)
@@ -127,7 +127,7 @@ internal:
// CHECK-NEXT: }
// CHECK-NEXT: Symbol {
// CHECK-NEXT: Name: zed
-// CHECK-NEXT: Value: 0x1008
+// CHECK-NEXT: Value: 0x3000
// CHECK-NEXT: Size: 0
// CHECK-NEXT: Binding: Global (0x1)
// CHECK-NEXT: Type: None
@@ -136,7 +136,7 @@ internal:
// CHECK-NEXT: }
// CHECK-NEXT: Symbol {
// CHECK-NEXT: Name: protected
-// CHECK-NEXT: Value: 0x1010
+// CHECK-NEXT: Value: 0x3008
// CHECK-NEXT: Size: 0
// CHECK-NEXT: Binding: Global
// CHECK-NEXT: Type: None
@@ -145,7 +145,7 @@ internal:
// CHECK-NEXT: }
// CHECK-NEXT: Symbol {
// CHECK-NEXT: Name: zed3
-// CHECK-NEXT: Value: 0x1010
+// CHECK-NEXT: Value: 0x3008
// CHECK-NEXT: Size: 4
// CHECK-NEXT: Binding: Global
// CHECK-NEXT: Type: None
@@ -154,7 +154,7 @@ internal:
// CHECK-NEXT: }
// CHECK-NEXT: Symbol {
// CHECK-NEXT: Name: zed2
-// CHECK-NEXT: Value: 0x100C
+// CHECK-NEXT: Value: 0x3004
// CHECK-NEXT: Size: 0
// CHECK-NEXT: Binding: Global
// CHECK-NEXT: Type: None
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