[ELF] - Don't segfault when assigning non-calculatable absolute symbol value.

[grimar]

Summary

This is PR32664.

Issue was revealed by linux kernel script which was:

SECTIONS {
 . = (0xffffffff80000000 + ALIGN(0x1000000, 0x200000));
 phys_startup_64 = ABSOLUTE(startup_64 - 0xffffffff80000000);

 .text : AT(ADDR(.text) - 0xffffffff80000000) {
.....
  *(.head.text)

Where startup_64 is in .head.text.

At the place of assignment to phys_startup_64 we can not calculate absolute value for startup_64
because .text section has no VA assigned. Two patches were prepared earlier to address this: D32173 and D32174.

And in comments for D32173 was suggested not try to support this case, but error out.

[ruiu]

ELF/LinkerScript.h

45 ↗

(On Diff #97591)

It failed with a segfault because OutSec is null if no address is assigned. So why do you need a new member variable? It seems you can check if OutSec is null.

[grimar]

• Addressed review comment.

[grimar]

ELF/LinkerScript.h

45 ↗

(On Diff #97591)

Yes, you right.

Do we want to add Location member to ExprValue ? ExprValue::getValue() may use it for producing better error reporting.

[ruiu]

LGTM

lld/trunk/ELF/LinkerScript.cpp

 using namespace llvm::object;
 using namespace llvm::support::endian;
 using namespace lld;
 using namespace lld::elf;
 
 LinkerScript *elf::Script;
 
 uint64_t ExprValue::getValue() const {
-  if (Sec)
+  if (Sec) {
+    if (Sec->getOutputSection())
       return Sec->getOffset(Val) + Sec->getOutputSection()->Addr;
+    error("unable to evaluate expression: input section " + Sec->Name +
+          " has no output section assigned");
+  }
   return Val;
 }
 
 uint64_t ExprValue::getSecAddr() const {
   if (Sec)
     return Sec->getOffset(0) + Sec->getOutputSection()->Addr;
   return 0;
 }

lld/trunk/test/ELF/linkerscript/early-assign-symbol.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+
+# RUN: echo "SECTIONS { aaa = 1 + ABSOLUTE(foo - 1); }" > %t1.script
+# RUN: not ld.lld -o %t --script %t1.script %t.o 2>&1 | FileCheck %s
+
+# RUN: echo "SECTIONS { aaa = ABSOLUTE(foo - 1) + 1; }" > %t2.script
+# RUN: not ld.lld -o %t --script %t2.script %t.o 2>&1 | FileCheck %s
+
+# CHECK: error: unable to evaluate expression: input section .text has no output section assigned
+
+.section .text
+.globl foo
+foo: