[ELF] - Do not crash when ALIGN/DATA_SEGMENT_ALIGN expression used with zero value.

[grimar]

Summary

Previously we would crash,
I suggest to use 1 value instead 0 in this case.
This looks to be consistent with GNU linkers
and reasonable and simple behavior itself.

[ruiu]

LGTM

lld/trunk/ELF/ScriptParser.cpp

if (Tok == "ADDR") {
     return [=]() -> ExprValue {
       return {checkSection(Cmd, Location), 0, Location};
     };
   }
   if (Tok == "ALIGN") {
     expect("(");
     Expr E = readExpr();
     if (consume(")"))
-      return [=] { return alignTo(Script->getDot(), E().getValue()); };
+      return [=] {
+        return alignTo(Script->getDot(), std::max((uint64_t)1, E().getValue()));
+      };
     expect(",");
     Expr E2 = readExpr();
     expect(")");
     return [=] {
       ExprValue V = E();
-      V.Alignment = E2().getValue();
+      V.Alignment = std::max((uint64_t)1, E2().getValue());
       return V;
     };
   }
   if (Tok == "ALIGNOF") {
     StringRef Name = readParenLiteral();
     OutputSection *Cmd = Script->getOrCreateOutputSection(Name);
     return [=] { return checkSection(Cmd, Location)->Alignment; };
   }
   if (Tok == "ASSERT")
     return readAssertExpr();
   if (Tok == "CONSTANT") {
     StringRef Name = readParenLiteral();
     return [=] { return getConstant(Name); };
   }
   if (Tok == "DATA_SEGMENT_ALIGN") {
     expect("(");
     Expr E = readExpr();
     expect(",");
     readExpr();
     expect(")");
-    return [=] { return alignTo(Script->getDot(), E().getValue()); };
+    return [=] {
+      return alignTo(Script->getDot(), std::max((uint64_t)1, E().getValue()));
+    };
   }
   if (Tok == "DATA_SEGMENT_END") {
     expect("(");
     expect(".");
     expect(")");
     return [] { return Script->getDot(); };
   }
   if (Tok == "DATA_SEGMENT_RELRO_END") {

lld/trunk/test/ELF/linkerscript/align.s

 # SYMBOLS-LABEL: SYMBOL TABLE:
 # SYMBOLS-NEXT: 0000000000000000         *UND*           00000000
 # SYMBOLS-NEXT: 0000000000014008         .text           00000000 _start
 # SYMBOLS-NEXT: 0000000000010000         *ABS*           00000000 __code_base__
 # SYMBOLS-NEXT: 0000000000001000         *ABS*           00000000 VAR
 # SYMBOLS-NEXT: 0000000000011000         .bbb            00000000 __start_bbb
 # SYMBOLS-NEXT: 0000000000012000         .bbb            00000000 __end_bbb
 
+## Check that ALIGN zero do nothing and does not crash #1.
+# RUN: echo "SECTIONS { . = ALIGN(0x123, 0); .aaa : { *(.aaa) } }" > %t.script
+# RUN: ld.lld -o %t4 --script %t.script %t
+# RUN: llvm-objdump -section-headers %t4 | FileCheck %s -check-prefix=ZERO
+
+# ZERO:      Sections:
+# ZERO-NEXT: Idx Name          Size      Address         Type
+# ZERO-NEXT:   0               00000000 0000000000000000
+# ZERO-NEXT:   1 .aaa          00000008 0000000000000123 DATA
+
+## Check that ALIGN zero do nothing and does not crash #2.
+# RUN: echo "SECTIONS { . = 0x123; . = ALIGN(0); .aaa : { *(.aaa) } }" > %t.script
+# RUN: ld.lld -o %t5 --script %t.script %t
+# RUN: llvm-objdump -section-headers %t5 | FileCheck %s -check-prefix=ZERO
+
 .global _start
 _start:
  nop
 
 .section .aaa, "a"
 .quad 0
 
 .section .bbb, "a"
 .quad 0
 
 .section .ccc, "a"
 .quad 0

lld/trunk/test/ELF/linkerscript/operators.s

 # RUN:  plusassign += 2; \
 # RUN:  unary = -1 + 3; \
 # RUN:  lshift = 1 << 5; \
 # RUN:  rshift = 0xff >> 3; \
 # RUN:  maxpagesize = CONSTANT (MAXPAGESIZE); \
 # RUN:  commonpagesize = CONSTANT (COMMONPAGESIZE); \
 # RUN:  . = 0xfff0; \
 # RUN:  datasegmentalign = DATA_SEGMENT_ALIGN (0xffff, 0); \
+# RUN:  datasegmentalign2 = DATA_SEGMENT_ALIGN (0, 0); \
 # RUN: }" > %t.script
 # RUN: ld.lld %t --script %t.script -o %t2
 # RUN: llvm-objdump -t %t2 | FileCheck %s
 
 # CHECK: 00000000000006 *ABS* 00000000 plus
 # CHECK: 00000000000004 *ABS* 00000000 minus
 # CHECK: 00000000000003 *ABS* 00000000 div
 # CHECK: 00000000000007 *ABS* 00000000 mul

 # CHECK: 00000000000002 *ABS* 00000000 neq
 # CHECK: 00000000000003 *ABS* 00000000 plusassign
 # CHECK: 00000000000002 *ABS* 00000000 unary
 # CHECK: 00000000000020 *ABS* 00000000 lshift
 # CHECK: 0000000000001f *ABS* 00000000 rshift
 # CHECK: 00000000001000 *ABS* 00000000 maxpagesize
 # CHECK: 00000000001000 *ABS* 00000000 commonpagesize
 # CHECK: 0000000000ffff *ABS* 00000000 datasegmentalign
+# CHECK: 0000000000fff0 *ABS* 00000000 datasegmentalign2
 
 ## Mailformed number error.
 # RUN: echo "SECTIONS { . = 0x12Q41; }" > %t.script
 # RUN: not ld.lld %t --script %t.script -o %t2 2>&1 | \
 # RUN:  FileCheck --check-prefix=NUMERR %s
 # NUMERR: malformed number: 0x12Q41
 
 ## Missing closing bracket.