[PATCH] D42550: Put the header in the first PT_LOAD even if that PT_LOAD has a LMAExpr

[Rafael Avila de Espindola via Phabricator via llvm-commits]

espindola created this revision.
espindola added reviewers: ruiu, grimar.
Herald added a subscriber: emaste.

This should fix

https://bugs.llvm.org/show_bug.cgi?id=36017

The root problem is that we were creating a PT_LOAD just for the header. That was technically valid, but inconvenient: we should not be making the ELF discontinuous.

The solution is to allow a section with LMAExpr to be added to a PT_LOAD if that PT_LOAD doesn't already have a LMAExpr.


https://reviews.llvm.org/D42550

Files:
  ELF/Writer.cpp
  ELF/Writer.h
  test/ELF/linkerscript/merge-header-load.s


Index: test/ELF/linkerscript/merge-header-load.s
===================================================================
--- /dev/null
+++ test/ELF/linkerscript/merge-header-load.s
@@ -0,0 +1,21 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+# RUN: echo "SECTIONS {                  \
+# RUN:  . = 0xffffffff80000200;          \
+# RUN:  .text : AT (0x4200) { *(.text) } \
+# RUN: }" > %t.script
+# RUN: ld.lld %t.o --script %t.script -o %t
+# RUN: llvm-readelf -program-headers %t | FileCheck %s
+
+# Test that we put the header in the first PT_LOAD. We used to create a PT_LOAD
+# just for it and it would have a different virtual to physical address delta.
+
+# CHECK: Program Headers:
+# CHECK:      Type  Offset   VirtAddr           PhysAddr
+# CHECK-NEXT: PHDR  0x000040 0xffffffff80000040 0x0000000000004040
+# CHECK-NEXT: LOAD  0x000000 0xffffffff80000000 0x0000000000004000
+# CHECK-NOT:  LOAD
+
+.global _start
+_start:
+nop
Index: ELF/Writer.h
===================================================================
--- ELF/Writer.h
+++ ELF/Writer.h
@@ -44,6 +44,7 @@
   OutputSection *FirstSec = nullptr;
   OutputSection *LastSec = nullptr;
   bool HasLMA = false;
+  bool ASectionHasLMA = false;
   uint64_t LMAOffset = 0;
 };
 
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -822,6 +822,8 @@
   p_align = std::max(p_align, Sec->Alignment);
   if (p_type == PT_LOAD)
     Sec->PtLoad = this;
+  if (Sec->LMAExpr)
+    ASectionHasLMA = true;
 }
 
 // The beginning and the ending of .rel[a].plt section are marked
@@ -1626,8 +1628,9 @@
     // different flags or is loaded at a discontiguous address using AT linker
     // script command.
     uint64_t NewFlags = computeFlags(Sec->getPhdrFlags());
-    if (Sec->LMAExpr || Sec->MemRegion != Load->FirstSec->MemRegion ||
-        Flags != NewFlags) {
+    if ((Sec->LMAExpr && Load->ASectionHasLMA) ||
+        Sec->MemRegion != Load->FirstSec->MemRegion || Flags != NewFlags) {
+
       Load = AddHdr(PT_LOAD, NewFlags);
       Flags = NewFlags;
     }


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