[ELF] Error if --strip-all and --emit-relocs are used together

[MaskRay]

Summary

--strip-all suppresses the creation of in.symtab
This can cause a null pointer dereference in OutputSection::finalize

// --emit-relocs => copyRelocs is true
if (!config->copyRelocs || (type != SHT_RELA && type != SHT_REL))
  return;
...
link = in.symTab->getParent()->sectionIndex; // in.symTab is null

Let's just disallow the combination.

In some cases:

• ld.bfd: final link failed: invalid operation
• gold: internal error in set_no_output_symtab_entry, at ../../gold/object.h:1814

[ruiu]

LGTM

ELF/Driver.cpp

if (!config->shared && !config->filterList.empty())
     error("-F may not be used without -shared");
 
   if (!config->shared && !config->auxiliaryList.empty())
     error("-f may not be used without -shared");
 
   if (!config->relocatable && !config->defineCommon)
     error("-no-define-common not supported in non relocatable output");
 
+  if (config->strip == StripPolicy::All && config->emitRelocs)
+    error("--strip-all and --emit-relocs may not be used together");
+
   if (config->zText && config->zIfuncNoplt)
     error("-z text and -z ifunc-noplt may not be used together");
 
   if (config->relocatable) {
     if (config->shared)
       error("-r and -shared may not be used together");
     if (config->gcSections)
       error("-r and --gc-sections may not be used together");

test/ELF/strip-all.s

 # Ignore --strip-all if -r is specified
 #RUN: ld.lld %t.o --strip-all -r -o %t1
 #RUN: llvm-objdump -section-headers %t1 | FileCheck %s -check-prefix BEFORE
 
 # Test alias -s
 #RUN: ld.lld %t.o -s -o %t1
 #RUN: llvm-objdump -section-headers %t1 | FileCheck %s -check-prefix AFTER
 
+# RUN: not ld.lld %t.o --strip-all --emit-relocs -o /dev/null 2>&1 | FileCheck --check-prefix=ERR %s
+# ERR: error: --strip-all and --emit-relocs may not be used together
+
 # exits with return code 42 on linux
 .globl _start
 _start:
   mov $60, %rax
   mov $42, %rdi
   syscall