[lld] r262019 - Description of symbols is avalable here:
George Rimar via llvm-commits
llvm-commits at lists.llvm.org
Fri Feb 26 06:36:36 PST 2016
Author: grimar
Date: Fri Feb 26 08:36:36 2016
New Revision: 262019
URL: http://llvm.org/viewvc/llvm-project?rev=262019&view=rev
Log:
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
Added:
lld/trunk/test/ELF/edata-etext.s
Modified:
lld/trunk/ELF/Symbols.cpp
lld/trunk/ELF/Symbols.h
lld/trunk/ELF/Writer.cpp
Modified: lld/trunk/ELF/Symbols.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Symbols.cpp?rev=262019&r1=262018&r2=262019&view=diff
==============================================================================
--- lld/trunk/ELF/Symbols.cpp (original)
+++ lld/trunk/ELF/Symbols.cpp Fri Feb 26 08:36:36 2016
@@ -214,6 +214,8 @@ std::unique_ptr<InputFile> Lazy::getMemb
}
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);
Modified: lld/trunk/ELF/Symbols.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Symbols.h?rev=262019&r1=262018&r2=262019&view=diff
==============================================================================
--- lld/trunk/ELF/Symbols.h (original)
+++ lld/trunk/ELF/Symbols.h Fri Feb 26 08:36:36 2016
@@ -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>
Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=262019&r1=262018&r2=262019&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Fri Feb 26 08:36:36 2016
@@ -914,20 +914,30 @@ template <class ELFT> void Writer<ELFT>:
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>:
// 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() {
Added: lld/trunk/test/ELF/edata-etext.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/edata-etext.s?rev=262019&view=auto
==============================================================================
--- lld/trunk/test/ELF/edata-etext.s (added)
+++ lld/trunk/test/ELF/edata-etext.s Fri Feb 26 08:36:36 2016
@@ -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
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