From c60b4510ea6db9726fd4870381ca8486d862e9b8 Mon Sep 17 00:00:00 2001
From: Peter Smith <peter.smith@linaro.org>
Date: Wed, 3 May 2017 08:44:50 +0000
Subject: [ELF] Fix problems with fabricateDefaultCommands() and
 --section-start

The --section-start <name>=<address> needs to be translated into equivalent
linker script commands. There are a couple of problems with the existing
implementation:
- The --section-start with the lowest address is assumed to be at the start
of the map. This assumption is incorrect, we have to iterate through the
SectionStartMap to find the lowest address.
- The addresses in --section-start were being over-aligned when the
sections were marked as PageAlign. This is inconsistent with the use of
SectionStartMap in fixHeaders(), and can cause problems when the PageAlign
causes an "unable to move location counter backward" error when the
--section-start with PageAlign is aligned to an address higher than the next
--section-start. The ld.bfd and ld.gold seem to be more consistent with this
approach but this is not a well specified area.

This change fixes the problems above and also corrects a typo in which
fabricateDefaultCommands() is called with the wrong parameter, it should be
called with AllocateHeader not Config->MaxPageSize.

Differential Revision: https://reviews.llvm.org/D32749

llvm-svn: 302007
---
 lld/ELF/LinkerScript.cpp | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

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

diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index 22a5b639469..3f872c65897 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -428,13 +428,12 @@ void LinkerScript::fabricateDefaultCommands(bool AllocateHeader) {
   if (AllocateHeader)
     StartAddr += elf::getHeaderSize();
 
-  // The Sections with -T<section> are sorted in order of ascending address
-  // we must use this if it is lower than StartAddr as calls to setDot() must
-  // be monotonically increasing
-  if (!Config->SectionStartMap.empty()) {
-    uint64_t LowestSecStart = Config->SectionStartMap.begin()->second;
-    StartAddr = std::min(StartAddr, LowestSecStart);
-  }
+  // The Sections with -T<section> have been sorted in order of ascending
+  // address. We must lower StartAddr if the lowest -T<section address> as
+  // calls to setDot() must be monotonically increasing.
+  for (auto& KV : Config->SectionStartMap)
+    StartAddr = std::min(StartAddr, KV.second);
+
   Commands.push_back(
       make<SymbolAssignment>(".", [=] { return StartAddr; }, ""));
 
@@ -444,17 +443,19 @@ void LinkerScript::fabricateDefaultCommands(bool AllocateHeader) {
     if (!(Sec->Flags & SHF_ALLOC))
       continue;
 
+    auto *OSCmd = make<OutputSectionCommand>(Sec->Name);
+    OSCmd->Sec = Sec;
+
+    // Prefer user supplied address over additional alignment constraint
     auto I = Config->SectionStartMap.find(Sec->Name);
     if (I != Config->SectionStartMap.end())
       Commands.push_back(
           make<SymbolAssignment>(".", [=] { return I->second; }, ""));
-
-    auto *OSCmd = make<OutputSectionCommand>(Sec->Name);
-    OSCmd->Sec = Sec;
-    if (Sec->PageAlign)
+    else if (Sec->PageAlign)
       OSCmd->AddrExpr = [=] {
         return alignTo(Script->getDot(), Config->MaxPageSize);
       };
+
     Commands.push_back(OSCmd);
     if (Sec->Sections.size()) {
       auto *ISD = make<InputSectionDescription>("");
-- 
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