replica
/
hanchenye-llvm-project
2
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

Description of symbols is avalable here: 

https://docs.oracle.com/cd/E53394_01/html/E54766/u-etext-3c.html

It is said that:
_etext - The address of _etext is the first 
location after the last read-only loadable segment.

_edata - The address of _edata is the first 
location after the last read-write loadable segment.

_end - If the address of _edata is greater than the address 
of _etext, the address of _end is same as the address of _edata.

In real life _end and _edata has different values for that case.
Both gold/bfd set _edata to the end of the last non SHT_NOBITS section.
This patch do the same for consistency.

It should fix the https://llvm.org/bugs/show_bug.cgi?id=26729.

Differential revision: http://reviews.llvm.org/D17601

llvm-svn: 262019
This commit is contained in:
George Rimar 2016-02-26 14:36:36 +00:00
parent a350e266aa
commit 9e8593949d
4 changed files with 154 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
lld/ELF/Symbols.cpp
View File

@ -214,6 +214,8 @@ std::unique_ptr<InputFile> Lazy::getMember() {
}
template <class ELFT> static void doInitSymbols() {
ElfSym<ELFT>::Etext.setBinding(STB_GLOBAL);
ElfSym<ELFT>::Edata.setBinding(STB_GLOBAL);
ElfSym<ELFT>::End.setBinding(STB_GLOBAL);
ElfSym<ELFT>::Ignored.setBinding(STB_WEAK);
ElfSym<ELFT>::Ignored.setVisibility(STV_HIDDEN);

8
lld/ELF/Symbols.h
View File

@ -346,6 +346,12 @@ template <class ELFT> struct ElfSym {
// output file's symbol table. It has weak binding and can be substituted.
static Elf_Sym Ignored;
// The content for _etext and etext symbols.
static Elf_Sym Etext;
// The content for _edata and edata symbols.
static Elf_Sym Edata;
// The content for _end and end symbols.
static Elf_Sym End;
@ -359,6 +365,8 @@ template <class ELFT> struct ElfSym {
};
template <class ELFT> typename ElfSym<ELFT>::Elf_Sym ElfSym<ELFT>::Ignored;
template <class ELFT> typename ElfSym<ELFT>::Elf_Sym ElfSym<ELFT>::Etext;
template <class ELFT> typename ElfSym<ELFT>::Elf_Sym ElfSym<ELFT>::Edata;
template <class ELFT> typename ElfSym<ELFT>::Elf_Sym ElfSym<ELFT>::End;
template <class ELFT> typename ElfSym<ELFT>::Elf_Sym ElfSym<ELFT>::MipsGp;
template <class ELFT>

33
lld/ELF/Writer.cpp
View File

@ -914,20 +914,30 @@ template <class ELFT> void Writer<ELFT>::addReservedSymbols() {
if (!isOutputDynamic())
Symtab.addIgnored("__tls_get_addr");
auto Define = [this](StringRef Name, StringRef Alias, Elf_Sym &Sym) {
if (Symtab.find(Name))
Symtab.addAbsolute(Name, Sym);
if (SymbolBody *B = Symtab.find(Alias))
if (B->isUndefined())
Symtab.addAbsolute(Alias, Sym);
};
// If the "_end" symbol is referenced, it is expected to point to the address
// right after the data segment. Usually, this symbol points to the end
// of .bss section or to the end of .data section if .bss section is absent.
// We don't know the final address of _end yet, so just add a symbol here,
// and fix ElfSym<ELFT>::End.st_value later.
if (Symtab.find("_end"))
Symtab.addAbsolute("_end", ElfSym<ELFT>::End);
// Define "end" as an alias to "_end" if it is used but not defined.
// We don't want to define that unconditionally because we don't want to
// break programs that uses "end" as a regular symbol.
if (SymbolBody *B = Symtab.find("end"))
if (B->isUndefined())
Symtab.addAbsolute("end", ElfSym<ELFT>::End);
// The similar history with _etext/etext and _edata/edata:
// Address of _etext is the first location after the last read-only loadable
// segment. Address of _edata points to the end of the last non SHT_NOBITS
// section. That is how gold/bfd do. We update the values for these symbols
// later, after assigning sections to segments.
Define("_end", "end", ElfSym<ELFT>::End);
Define("_etext", "etext", ElfSym<ELFT>::Etext);
Define("_edata", "edata", ElfSym<ELFT>::Edata);
}
// Sort input sections by section name suffixes for
@ -1454,6 +1464,17 @@ template <class ELFT> void Writer<ELFT>::fixAbsoluteSymbols() {
// Update MIPS _gp absolute symbol so that it points to the static data.
if (Config->EMachine == EM_MIPS)
ElfSym<ELFT>::MipsGp.st_value = getMipsGpAddr<ELFT>();
// _etext points to location after the last read-only loadable segment.
// _edata points to the end of the last non SHT_NOBITS section.
for (OutputSectionBase<ELFT> *Sec : OutputSections) {
if (!(Sec->getFlags() & SHF_ALLOC))
continue;
if (!(Sec->getFlags() & SHF_WRITE))
ElfSym<ELFT>::Etext.st_value = Sec->getVA() + Sec->getSize();
if (Sec->getType() != SHT_NOBITS)
ElfSym<ELFT>::Edata.st_value = Sec->getVA() + Sec->getSize();
}
}
template <class ELFT> void Writer<ELFT>::writeHeader() {

117
lld/test/ELF/edata-etext.s Normal file
View File

@ -0,0 +1,117 @@
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
# RUN: ld.lld %t.o -o %t
# RUN: llvm-readobj -sections -symbols %t | FileCheck %s
## This checks that:
## 1) Address of _etext is the first location after the last read-only loadable segment.
## 2) Address of _edata points to the end of the last non SHT_NOBITS section.
## That is how gold/bfd do. At the same time specs says: "If the address of _edata is
## greater than the address of _etext, the address of _end is same as the address
## of _edata." (https://docs.oracle.com/cd/E53394_01/html/E54766/u-etext-3c.html).
## 3) Address of _end is different from _edata because of 2.
# CHECK: Section {
# CHECK: Index: 1
# CHECK: Name: .text
# CHECK-NEXT: Type: SHT_PROGBITS
# CHECK-NEXT: Flags [
# CHECK-NEXT: SHF_ALLOC
# CHECK-NEXT: SHF_EXECINSTR
# CHECK-NEXT: ]
# CHECK-NEXT: Address: 0x11000
# CHECK-NEXT: Offset: 0x1000
# CHECK-NEXT: Size: 1
# CHECK-NEXT: Link:
# CHECK-NEXT: Info:
# CHECK-NEXT: AddressAlignment:
# CHECK-NEXT: EntrySize: 0
# CHECK-NEXT: }
# CHECK-NEXT: Section {
# CHECK-NEXT: Index: 2
# CHECK-NEXT: Name: .data
# CHECK-NEXT: Type: SHT_PROGBITS
# CHECK-NEXT: Flags [
# CHECK-NEXT: SHF_ALLOC
# CHECK-NEXT: SHF_WRITE
# CHECK-NEXT: ]
# CHECK-NEXT: Address: 0x12000
# CHECK-NEXT: Offset: 0x2000
# CHECK-NEXT: Size: 2
# CHECK-NEXT: Link:
# CHECK-NEXT: Info:
# CHECK-NEXT: AddressAlignment:
# CHECK-NEXT: EntrySize:
# CHECK-NEXT: }
# CHECK-NEXT: Section {
# CHECK-NEXT: Index: 3
# CHECK-NEXT: Name: .bss
# CHECK-NEXT: Type: SHT_NOBITS
# CHECK-NEXT: Flags [
# CHECK-NEXT: SHF_ALLOC
# CHECK-NEXT: SHF_WRITE
# CHECK-NEXT: ]
# CHECK-NEXT: Address: 0x12004
# CHECK-NEXT: Offset: 0x2002
# CHECK-NEXT: Size: 6
# CHECK-NEXT: Link:
# CHECK-NEXT: Info:
# CHECK-NEXT: AddressAlignment:
# CHECK-NEXT: EntrySize:
# CHECK-NEXT: }
# CHECK: Symbols [
# CHECK-NEXT: Symbol {
# CHECK-NEXT: Name:
# CHECK-NEXT: Value: 0x0
# CHECK-NEXT: Size: 0
# CHECK-NEXT: Binding: Local
# CHECK-NEXT: Type: None
# CHECK-NEXT: Other: 0
# CHECK-NEXT: Section: Undefined
# CHECK-NEXT: }
# CHECK-NEXT: Symbol {
# CHECK-NEXT: Name: _start
# CHECK-NEXT: Value: 0x11000
# CHECK-NEXT: Size: 0
# CHECK-NEXT: Binding: Global
# CHECK-NEXT: Type: None
# CHECK-NEXT: Other: 0
# CHECK-NEXT: Section: .text
# CHECK-NEXT: }
# CHECK-NEXT: Symbol {
# CHECK-NEXT: Name: _edata
# CHECK-NEXT: Value: 0x12002
# CHECK-NEXT: Size: 0
# CHECK-NEXT: Binding: Global
# CHECK-NEXT: Type: None
# CHECK-NEXT: Other: 0
# CHECK-NEXT: Section: Absolute
# CHECK-NEXT: }
# CHECK-NEXT: Symbol {
# CHECK-NEXT: Name: _end
# CHECK-NEXT: Value: 0x1200A
# CHECK-NEXT: Size: 0
# CHECK-NEXT: Binding: Global
# CHECK-NEXT: Type: None
# CHECK-NEXT: Other: 0
# CHECK-NEXT: Section: Absolute
# CHECK-NEXT: }
# CHECK-NEXT: Symbol {
# CHECK-NEXT: Name: _etext
# CHECK-NEXT: Value: 0x11001
# CHECK-NEXT: Size: 0
# CHECK-NEXT: Binding: Global
# CHECK-NEXT: Type: None
# CHECK-NEXT: Other: 0
# CHECK-NEXT: Section: Absolute
# CHECK-NEXT: }
# CHECK-NEXT: ]
.global _start,_end,_etext,_edata
.text
_start:
nop
.data
.word 1
.bss
.align 4
.space 6