[lld] r310886 - Update comments as the function does not write to the first page anymore.

[Rui Ueyama via llvm-commits]

Author: ruiu
Date: Mon Aug 14 14:18:12 2017
New Revision: 310886

URL: http://llvm.org/viewvc/llvm-project?rev=310886&view=rev
Log:
Update comments as the function does not write to the first page anymore.

Also refactored the code a bit.

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=310886&r1=310885&r2=310886&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Mon Aug 14 14:18:12 2017
@@ -1851,31 +1851,31 @@ template <class ELFT> void Writer<ELFT>:
       Sec->writeTo<ELFT>(Buf + Sec->Offset);
 }
 
-static void fillTrapInstr(uint8_t *I, uint8_t *End) {
+static void fillTrap(uint8_t *I, uint8_t *End) {
   for (; I + 4 < End; I += 4)
     memcpy(I, &Target->TrapInstr, 4);
 }
 
-
-// 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.
+// Fill 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.
+//
+// We'll leave other pages in segments as-is because the rest will be
+// overwritten by output sections.
 template <class ELFT> void Writer<ELFT>::writeTrapInstr() {
   if (Script->Opt.HasSections)
     return;
 
+  // Fill the last page.
   uint8_t *Buf = Buffer->getBufferStart();
+  for (PhdrEntry *P : Phdrs)
+    if (P->p_type == PT_LOAD && (P->p_flags & PF_X))
+      fillTrap(Buf + alignDown(P->p_offset + P->p_filesz, Target->PageSize),
+               Buf + alignTo(P->p_offset + P->p_filesz, Target->PageSize));
 
-  for (PhdrEntry *P : Phdrs) {
-    if (P->p_type != PT_LOAD || !(P->p_flags & PF_X))
-      continue;
-
-    // We only fill the last page of the segment because the rest will be
-    // overwritten by output sections.
-    fillTrapInstr(Buf + alignDown(P->p_offset + P->p_filesz, Target->PageSize),
-                  Buf + alignTo(P->p_offset + P->p_filesz, Target->PageSize));
-  }
-
+  // Round up the file size of the last segment to the page boundary iff it is
+  // an executable segment to ensure that other other tools don't accidentally
+  // trim the instruction padding (e.g. when stripping the file).
   PhdrEntry *LastRX = nullptr;
   for (PhdrEntry *P : Phdrs) {
     if (P->p_type != PT_LOAD)
@@ -1885,10 +1885,6 @@ template <class ELFT> void Writer<ELFT>:
     else
       LastRX = nullptr;
   }
-
-  // Round up the file size of the last segment to the page boundary iff it is
-  // an executable segment to ensure that other other tools don't accidentally
-  // trim the instruction padding (e.g. when stripping the file).
   if (LastRX)
     LastRX->p_filesz = alignTo(LastRX->p_filesz, Target->PageSize);
 }