[lld] r288580 - [ELF] - Change the way how we compute offsets for binary output.

[George Rimar via llvm-commits]

Author: grimar
Date: Sat Dec  3 01:23:30 2016
New Revision: 288580

URL: http://llvm.org/viewvc/llvm-project?rev=288580&view=rev
Log:
[ELF] - Change the way how we compute offsets for binary output.

Binary output feature is a bit confuzing. bfd and gold output differs a lot sometimes,
though it is important for FreeBSD mbr loaders.

Patch change the way how we compute file offsets for binary output.
This fixes PR31196.

Previously offsets were calculated basing on offsets and addresses of sections
from the same loads:
if (Sec == First)
  return alignTo(Off, Target->MaxPageSize, Sec->Addr);
return First->Offset + Sec->Addr - First->Addr;

bfd assigns offsets for each section to VA - MinVA:
https://github.com/redox-os/binutils-gdb/blob/master/bfd/binary.c#L27
https://github.com/redox-os/binutils-gdb/blob/master/bfd/binary.c#L255 
(LMA == VA usually)

This patch for now just stops creating phdrs for binary output. 
An effect from this that no any additional calculation for offset is performed:

uintX_t getFileAlignment(uintX_t Off, OutputSectionBase *Sec) {
OutputSectionBase *First = Sec->FirstInPtLoad;
// If the section is not in a PT_LOAD, we have no other constraint.
if (!First)
  return Off; //**First is always null, condition always happens**

That is enough now with combination of another patch to generate output
that is similar to what bfd produce for mbr loader.

Differential revision: https://reviews.llvm.org/D27341

Added:
    lld/trunk/test/ELF/oformat-binary-ttext.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=288580&r1=288579&r2=288580&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Sat Dec  3 01:23:30 2016
@@ -180,10 +180,15 @@ template <class ELFT> void Writer<ELFT>:
   if (Config->Relocatable) {
     assignFileOffsets();
   } else {
-    Phdrs = Script<ELFT>::X->hasPhdrsCommands() ? Script<ELFT>::X->createPhdrs()
-                                                : createPhdrs();
-    addPtArmExid(Phdrs);
-    fixHeaders();
+    // Binary output does not have PHDRS.
+    if (!Config->OFormatBinary) {
+      Phdrs = Script<ELFT>::X->hasPhdrsCommands()
+                  ? Script<ELFT>::X->createPhdrs()
+                  : createPhdrs();
+      addPtArmExid(Phdrs);
+      fixHeaders();
+    }
+
     if (ScriptConfig->HasSections) {
       Script<ELFT>::X->assignAddresses(Phdrs);
     } else {

Added: lld/trunk/test/ELF/oformat-binary-ttext.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/oformat-binary-ttext.s?rev=288580&view=auto
==============================================================================
--- lld/trunk/test/ELF/oformat-binary-ttext.s (added)
+++ lld/trunk/test/ELF/oformat-binary-ttext.s Sat Dec  3 01:23:30 2016
@@ -0,0 +1,18 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+
+# RUN: ld.lld -N -Ttext 0x100 -o %t.out %t --oformat binary
+# RUN: od -t x1 -v %t.out | FileCheck %s --check-prefix=BIN
+
+# BIN:      0000000 90 00 00 00 00 00 00 00
+# BIN-NEXT: 0000010
+# BIN-NOT:  0000020
+
+## The same but without OMAGIC.
+# RUN: ld.lld -Ttext 0x100 -o %t.out %t --oformat binary
+# RUN: od -t x1 -v %t.out | FileCheck %s --check-prefix=BIN
+
+.text
+.globl _start
+_start:
+ nop