From e75b42ee4ef0ed54d73a93c66f8bb9e9ed4e7006 Mon Sep 17 00:00:00 2001
From: Rafael Espindola <rafael.espindola@gmail.com>
Date: Thu, 1 Mar 2018 15:25:46 +0000
Subject: Don't allocate a header bellow address 0.

With the current code if the script has a PHDRS we always obey and try
to allocate a header. This can cause Min - HeaderSize to underflow.

It looks like bfd actually prints an error for this case. With this
patch we do the same.

Found while looking at pr36515.

llvm-svn: 326441
---
 lld/ELF/LinkerScript.cpp | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

(limited to 'lld/ELF/LinkerScript.cpp')

diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index 6aae9e6975d..f1a6d6381f1 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -897,6 +897,15 @@ static OutputSection *findFirstSection(PhdrEntry *Load) {
   return nullptr;
 }
 
+static uint64_t computeBase(uint64_t Min, bool AllocateHeaders) {
+  // If there is no SECTIONS or if the linkerscript is explicit about program
+  // headers, do our best to allocate them.
+  if (!Script->HasSectionsCommand || AllocateHeaders)
+    return 0;
+  // Otherwise only allocate program headers if that would not add a page.
+  return alignDown(Min, Config->MaxPageSize);
+}
+
 // Try to find an address for the file and program headers output sections,
 // which were unconditionally added to the first PT_LOAD segment earlier.
 //
@@ -920,17 +929,22 @@ void LinkerScript::allocateHeaders(std::vector<PhdrEntry *> &Phdrs) {
     return;
   PhdrEntry *FirstPTLoad = *It;
 
+  bool HasExplicitHeaders =
+      llvm::any_of(PhdrsCommands, [](const PhdrsCommand &Cmd) {
+        return Cmd.HasPhdrs || Cmd.HasFilehdr;
+      });
   uint64_t HeaderSize = getHeaderSize();
-  // When linker script with SECTIONS is being used, don't output headers
-  // unless there's a space for them.
-  uint64_t Base = HasSectionsCommand ? alignDown(Min, Config->MaxPageSize) : 0;
-  if (HeaderSize <= Min - Base || Script->hasPhdrsCommands()) {
+  if (HeaderSize <= Min - computeBase(Min, HasExplicitHeaders)) {
     Min = alignDown(Min - HeaderSize, Config->MaxPageSize);
     Out::ElfHeader->Addr = Min;
     Out::ProgramHeaders->Addr = Min + Out::ElfHeader->Size;
     return;
   }
 
+  // Error if we were explicitly asked to allocate headers.
+  if (HasExplicitHeaders)
+    error("could not allocate headers");
+
   Out::ElfHeader->PtLoad = nullptr;
   Out::ProgramHeaders->PtLoad = nullptr;
   FirstPTLoad->FirstSec = findFirstSection(FirstPTLoad);
-- 
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