[ELF2] Fix binaries so they actually run on FreeBSD.

Since FreeBSD 4.1, the kernel expects binaries to be marked with ELFOSABI_FREEBSD in the ELF header to exec() them. LLD unconditionally sets OSABI to ELF_OSABINONE, and everything linked with it won't run on FreeBSD (unless explicitly rebranded). Example: % ./aarch64-hello ELF binary type "0" not known. zsh: exec format error: ./aarch64-hello FreeBSD could be modified to accept ELF_OSABINONE, but that would break all existing binaries, so the kernel needs to support both ABINONE and ABIFREEBSD. I plan to push this change in FreeBSD one day, which, unfortunately, is not today. This code patches lld so it sets the header field correctly. For completeness, the rationale of this change is explained in the FreeBSD commit message, and it's apparently to pleasee binutils maintainers at the time. https://svnweb.freebsd.org/base?view=revision&revision=59342 Differential Revision: http://reviews.llvm.org/D13140 llvm-svn: 248554
llvm · Sep 25, 2015 · aa7c533 · aa7c533
1 parent 8aa9973
commit aa7c533
Show file tree

Hide file tree

Showing 3 changed files with 32 additions and 3 deletions.
diff --git a/lld/ELF/InputFiles.h b/lld/ELF/InputFiles.h
@@ -105,6 +105,9 @@ template <class ELFT> class ELFData {
   llvm::object::ELFFile<ELFT> &getObj() { return ELFObj; }
 
   uint16_t getEMachine() const { return getObj().getHeader()->e_machine; }
+  uint8_t getOSABI() const {
+    return getObj().getHeader()->e_ident[llvm::ELF::EI_OSABI];
+  }
 
   StringRef getStringTable() const { return StringTable; }
 

diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
@@ -500,14 +500,15 @@ template <class ELFT> void Writer<ELFT>::writeHeader() {
                                ? ELFDATA2LSB
                                : ELFDATA2MSB;
   EHdr->e_ident[EI_VERSION] = EV_CURRENT;
-  EHdr->e_ident[EI_OSABI] = ELFOSABI_NONE;
+
+  const SymbolTable &Symtab = SymTabSec.getSymTable();
+  auto &FirstObj = cast<ObjectFile<ELFT>>(*Symtab.getFirstELF());
+  EHdr->e_ident[EI_OSABI] = FirstObj.getOSABI();
 
   // FIXME: Generalize the segment construction similar to how we create
   // output sections.
-  const SymbolTable &Symtab = SymTabSec.getSymTable();
 
   EHdr->e_type = Config->Shared ? ET_DYN : ET_EXEC;
-  auto &FirstObj = cast<ObjectFile<ELFT>>(*Symtab.getFirstELF());
   EHdr->e_machine = FirstObj.getEMachine();
   EHdr->e_version = EV_CURRENT;
   SymbolBody *Entry = Symtab.getEntrySym();

diff --git a/lld/test/elf2/basic-freebsd.s b/lld/test/elf2/basic-freebsd.s
@@ -0,0 +1,25 @@
+# Verify that OSABI is set to the correct value.
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-freebsd %s -o %t
+# RUN: lld -flavor gnu2 %t -o %t2
+# RUN: llvm-readobj -file-headers %t2 | FileCheck %s
+# REQUIRES: x86
+
+.globl _start
+_start:
+  mov $1, %rax
+  mov $42, %rdi
+  syscall
+
+# CHECK: ElfHeader {
+# CHECK-NEXT:   Ident {
+# CHECK-NEXT:     Magic: (7F 45 4C 46)
+# CHECK-NEXT:     Class: 64-bit (0x2)
+# CHECK-NEXT:     DataEncoding: LittleEndian (0x1)
+# CHECK-NEXT:     FileVersion: 1
+# CHECK-NEXT:     OS/ABI: FreeBSD (0x9)
+# CHECK-NEXT:     ABIVersion: 0
+# CHECK-NEXT:     Unused: (00 00 00 00 00 00 00)
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Type: Executable (0x2)
+# CHECK-NEXT:   Machine: EM_X86_64 (0x3E)