[ELF] - Linkerscript: fix issue with SUBALIGN.

This is PR34886.

SUBALIGN command currently triggers failture if result expression
is zero. Patch fixes the issue, treating zero as 1, what is consistent with
other places and ELF spec it seems.

Patch also adds "is power of 2" check for this and other expressions
returning alignment.

Differential revision: https://reviews.llvm.org/D38846

llvm-svn: 316580

1 files changed, 20 insertions, 8 deletions

diff --git a/lld/ELF/ScriptParser.cpp b/lld/ELF/ScriptParser.cpp
index 5582ce672fb..903be2f503c 100644
--- a/lld/ELF/ScriptParser.cpp
+++ b/lld/ELF/ScriptParser.cpp
@@ -642,6 +642,17 @@ void ScriptParser::readSectionAddressType(OutputSection *Cmd) {
   }
 }
 
+static Expr checkAlignment(Expr E, std::string &Loc) {
+  return [=] {
+    uint64_t Alignment = std::max((uint64_t)1, E().getValue());
+    if (!isPowerOf2_64(Alignment)) {
+      error(Loc + ": alignment must be power of 2");
+      return (uint64_t)1; // Return a dummy value.
+    }
+    return Alignment;
+  };
+}
+
 OutputSection *ScriptParser::readOutputSectionDescription(StringRef OutSec) {
   OutputSection *Cmd =
       Script->createOutputSection(OutSec, getCurrentLocation());
@@ -650,12 +661,13 @@ OutputSection *ScriptParser::readOutputSectionDescription(StringRef OutSec) {
     readSectionAddressType(Cmd);
   expect(":");
 
+  std::string Location = getCurrentLocation();
   if (consume("AT"))
     Cmd->LMAExpr = readParenExpr();
   if (consume("ALIGN"))
-    Cmd->AlignExpr = readParenExpr();
+    Cmd->AlignExpr = checkAlignment(readParenExpr(), Location);
   if (consume("SUBALIGN"))
-    Cmd->SubalignExpr = readParenExpr();
+    Cmd->SubalignExpr = checkAlignment(readParenExpr(), Location);
 
   // Parse constraints.
   if (consume("ONLY_IF_RO"))
@@ -959,16 +971,16 @@ Expr ScriptParser::readPrimary() {
   if (Tok == "ALIGN") {
     expect("(");
     Expr E = readExpr();
-    if (consume(")"))
-      return [=] {
-        return alignTo(Script->getDot(), std::max((uint64_t)1, E().getValue()));
-      };
+    if (consume(")")) {
+      E = checkAlignment(E, Location);
+      return [=] { return alignTo(Script->getDot(), E().getValue()); };
+    }
     expect(",");
-    Expr E2 = readExpr();
+    Expr E2 = checkAlignment(readExpr(), Location);
     expect(")");
     return [=] {
       ExprValue V = E();
-      V.Alignment = std::max((uint64_t)1, E2().getValue());
+      V.Alignment = E2().getValue();
       return V;
     };
   }