[ELF] - Do not forget to fill last bytes of PT_LOADs with trap instructions.

[grimar]

Summary

D33630 implemented filling load segments with trap,
but it has bug - it forgets to set last 4 bytes.
Patch fixes the issue.

[ruiu]

ELF/OutputSections.cpp

310

This function is so small that you don't want to share. Just copy the contents.

test/ELF/build-id.s

50–59

These tests don't really test the thing you want to test. Please write a real test.

[grimar]

• Addressd review comments.

[grimar]

ping

[ruiu]

ELF/Writer.cpp

1832–1833

We can safely assume that End-I is a multiple of 4. So you want to change < to <= instead of adding a new line of code, no?

[grimar]

• Addressed review comment.

ELF/Writer.cpp

1832–1833

Yes. And then what about inlining fillTrapInstr?

[ruiu]

ELF/Writer.cpp

1832–1833

I think I still prefer outlining it.

[grimar]

• Addressed review comment.

[ruiu]

LGTM

ELF/LinkerScript.h

public:
   void processCommands(OutputSectionFactory &Factory);
 
   // Parsed linker script configurations are set to this struct.
   ScriptConfiguration Opt;
 };
 
 extern LinkerScript *Script;
 
+void fill(uint8_t *Buf, size_t Size, uint32_t Filler);
+
 } // end namespace elf
 } // end namespace lld
 
 #endif // LLD_ELF_LINKER_SCRIPT_H

ELF/OutputSections.cpp

void OutputSection::sort(std::function<int(InputSectionBase *S)> Order) {
   std::stable_sort(V.begin(), V.end(), Comp);
   ISD->Sections.clear();
   for (Pair &P : V)
     ISD->Sections.push_back(P.second);
 }
 
 // Fill [Buf, Buf + Size) with Filler.
 // This is used for linker script "=fillexp" command.
-static void fill(uint8_t *Buf, size_t Size, uint32_t Filler) {
+void elf::fill(uint8_t *Buf, size_t Size, uint32_t Filler) {
   size_t I = 0;
   for (; I + 4 < Size; I += 4)
     memcpy(Buf + I, &Filler, 4);
   memcpy(Buf + I, &Filler, Size - I);
 }
 
 // Compress section contents if this section contains debug info.
 template <class ELFT> void OutputSection::maybeCompress() {

ELF/Writer.cpp

 }
 
 template <class ELFT> void Writer<ELFT>::writeSectionsBinary() {
   uint8_t *Buf = Buffer->getBufferStart();
   for (OutputSection *Sec : OutputSections)
     if (Sec->Flags & SHF_ALLOC)
       Sec->writeTo<ELFT>(Buf + Sec->Offset);
 }
 
-static void fillTrapInstr(uint8_t *I, uint8_t *End) {
-  for (; I + 4 < End; I += 4)
-    memcpy(I, &Target->TrapInstr, 4);
+static void fillPage(uint8_t *Buf, uint64_t Offset, uint32_t Filler) {
+  uint64_t Begin = alignDown(Offset, Target->PageSize);
+  uint64_t End = alignTo(Offset, Target->PageSize);
+  fill(Buf + Begin, End - Begin, Filler);
 }
 
-
 // Fill the first and the last page of executable segments with trap
 // instructions instead of leaving them as zero. Even though it is not required
 // by any standard , it is in general a good thing to do for security reasons.
 template <class ELFT> void Writer<ELFT>::writeTrapInstr() {
   if (Script->Opt.HasSections)
     return;
 
   uint8_t *Buf = Buffer->getBufferStart();
 
   for (PhdrEntry *P : Phdrs) {
     if (P->p_type != PT_LOAD || !(P->p_flags & PF_X))
       continue;
 
     // We only fill the first and the last page of the segment because the
     // middle part will be overwritten by output sections.
-    fillTrapInstr(Buf + alignDown(P->p_offset, Target->PageSize),
-                  Buf + alignTo(P->p_offset, Target->PageSize));
-    fillTrapInstr(Buf + alignDown(P->p_offset + P->p_filesz, Target->PageSize),
-                  Buf + alignTo(P->p_offset + P->p_filesz, Target->PageSize));
+    fillPage(Buf, P->p_offset, Target->TrapInstr);
+    fillPage(Buf, P->p_offset + P->p_filesz, Target->TrapInstr);
   }
 
   PhdrEntry *LastRX = nullptr;
   for (PhdrEntry *P : Phdrs) {
     if (P->p_type != PT_LOAD)
       continue;
     if (P->p_flags & PF_X)
       LastRX = P;

test/ELF/build-id.s

 _start:
   nop
 
 .section .note.test, "a", @note
    .quad 42
 
 # DEFAULT:      Contents of section .note.test:
 # DEFAULT:      Contents of section .note.gnu.build-id:
 # DEFAULT-NEXT: 04000000 08000000 03000000 474e5500  ............GNU.
-# DEFAULT-NEXT: d618a375 bc6301ec
+# DEFAULT-NEXT: b0148597 ba5eb7e9
 
 # MD5:      Contents of section .note.gnu.build-id:
 # MD5-NEXT: 04000000 10000000 03000000 474e5500  ............GNU.
-# MD5-NEXT: 051084fe ce1f30ed e035b79e 11262808
+# MD5-NEXT: dce3bcaf 5219454c e89a1fc7 86ab17bd
 
 # SHA1:      Contents of section .note.gnu.build-id:
 # SHA1-NEXT: 04000000 14000000 03000000 474e5500  ............GNU.
-# SHA1-NEXT: c70b9aec 903fd291 8b677cd8 1e04f8b6
+# SHA1-NEXT: 2f716666 fe3668fe 370a02a1 579c3eb2
 
 # UUID:      Contents of section .note.gnu.build-id:
 # UUID-NEXT: 04000000 10000000 03000000 474e5500  ............GNU.
 
 # HEX:      Contents of section .note.gnu.build-id:
 # HEX-NEXT: 04000000 04000000 03000000 474e5500  ............GNU.
 # HEX-NEXT: 12345678
 
 # NONE-NOT: Contents of section .note.gnu.build-id: