[lld] r288808 - Don't print empty PT_LOAD.

[Rafael Espindola via llvm-commits]

Author: rafael
Date: Tue Dec  6 07:43:34 2016
New Revision: 288808

URL: http://llvm.org/viewvc/llvm-project?rev=288808&view=rev
Log:
Don't print empty PT_LOAD.

If we do, the freebsd dynamic linker tries to call mmap with a size 0,
which fails.

It is hard to avoid creating them when linker scripts are used, so we
just delete empty PT_LOADs at the end.

Added:
    lld/trunk/test/ELF/empty-pt-load.s
Modified:
    lld/trunk/ELF/Writer.cpp
    lld/trunk/test/ELF/program-header-layout.s

Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=288808&r1=288807&r2=288808&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Tue Dec  6 07:43:34 2016
@@ -62,6 +62,7 @@ private:
   void addPredefinedSections();
 
   std::vector<Phdr> createPhdrs();
+  void removeEmptyPTLoad();
   void addPtArmExid(std::vector<Phdr> &Phdrs);
   void assignAddresses();
   void assignFileOffsets();
@@ -134,6 +135,16 @@ template <class ELFT> static bool needsI
 
 template <class ELFT> void elf::writeResult() { Writer<ELFT>().run(); }
 
+template <class ELFT> void Writer<ELFT>::removeEmptyPTLoad() {
+  auto I = std::remove_if(Phdrs.begin(), Phdrs.end(), [&](const Phdr &P) {
+    if (P.H.p_type != PT_LOAD)
+      return false;
+    uintX_t Size = P.Last->Addr + P.Last->Size - P.First->Addr;
+    return Size == 0;
+  });
+  Phdrs.erase(I, Phdrs.end());
+}
+
 // The main function of the writer.
 template <class ELFT> void Writer<ELFT>::run() {
   // Create linker-synthesized sections such as .got or .plt.
@@ -198,6 +209,11 @@ template <class ELFT> void Writer<ELFT>:
       assignAddresses();
     }
 
+    // Remove empty PT_LOAD to avoid causing the dynamic linker to try to mmap a
+    // 0 sized region. This has to be done late since only after assignAddresses
+    // we know the size of the sections.
+    removeEmptyPTLoad();
+
     if (!Config->OFormatBinary)
       assignFileOffsets();
     else

Added: lld/trunk/test/ELF/empty-pt-load.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/empty-pt-load.s?rev=288808&view=auto
==============================================================================
--- lld/trunk/test/ELF/empty-pt-load.s (added)
+++ lld/trunk/test/ELF/empty-pt-load.s Tue Dec  6 07:43:34 2016
@@ -0,0 +1,11 @@
+// REQUIRES: x86
+// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+// RUN: ld.lld %t.o -o %t.so -shared
+// RUN: llvm-readobj -l --elf-output-style=GNU %t.so | FileCheck %s
+
+// Test that we don't create an empty executable PT_LOAD.
+
+// CHECK:      PHDR    {{.*}} R   0x8
+// CHECK-NEXT: LOAD    {{.*}} R   0x1000
+// CHECK-NEXT: LOAD    {{.*}} RW  0x1000
+// CHECK-NEXT: DYNAMIC {{.*}} RW  0x8

Modified: lld/trunk/test/ELF/program-header-layout.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/program-header-layout.s?rev=288808&r1=288807&r2=288808&view=diff
==============================================================================
--- lld/trunk/test/ELF/program-header-layout.s (original)
+++ lld/trunk/test/ELF/program-header-layout.s Tue Dec  6 07:43:34 2016
@@ -61,19 +61,6 @@ _start:
 # CHECK-NEXT:     Offset:
 # CHECK-NEXT:     VirtualAddress:
 # CHECK-NEXT:     PhysicalAddress:
-# CHECK-NEXT:     FileSize: 0
-# CHECK-NEXT:     MemSize: 0
-# CHECK-NEXT:     Flags [
-# CHECK-NEXT:       PF_R
-# CHECK-NEXT:       PF_X
-# CHECK-NEXT:     ]
-# CHECK-NEXT:     Alignment:
-# CHECK-NEXT:   }
-# CHECK-NEXT:   ProgramHeader {
-# CHECK-NEXT:     Type: PT_LOAD
-# CHECK-NEXT:     Offset:
-# CHECK-NEXT:     VirtualAddress:
-# CHECK-NEXT:     PhysicalAddress:
 # CHECK-NEXT:     FileSize: 16
 # CHECK-NEXT:     MemSize: 16
 # CHECK-NEXT:     Flags [