[ELF] Support -z common-page-size option

[phosek]

Summary

This option is already supported by both BFD ld and gold and allows overriding the page size whose default value is defined by the target.

[davide]

The code for overriding max-page-size and common-page-size is nearly identical. Can you think of a way of sharing/factoring it out?

[phosek]

Please take a look at the updated version of https://reviews.llvm.org/D24891, if you prefer that one I'll abandon this one.

[davide]

In D24898#551782, @phosek wrote:

Please take a look at the updated version of https://reviews.llvm.org/D24891, if you prefer that one I'll abandon this one.

Yes, please abandon this one.

ELF/Config.h

struct Configuration {
   bool ZOrigin;
   bool ZRelro;
   DiscardPolicy Discard;
   SortSectionPolicy SortSection;
   StripPolicy Strip = StripPolicy::None;
   UnresolvedPolicy UnresolvedSymbols;
   BuildIdKind BuildId = BuildIdKind::None;
   ELFKind EKind = ELFNoneKind;
+  uint64_t CommonPageSize;
   uint16_t DefaultSymbolVersion = llvm::ELF::VER_NDX_GLOBAL;
   uint16_t EMachine = llvm::ELF::EM_NONE;
   uint64_t EntryAddr = 0;
   uint64_t ImageBase;
   uint64_t ZStackSize = -1;
   unsigned LtoJobs;
   unsigned LtoO;
   unsigned Optimize;

ELF/Driver.cpp

template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
   // Default output filename is "a.out" by the Unix tradition.
   if (Config->OutputFile.empty())
     Config->OutputFile = "a.out";
 
   // Handle --trace-symbol.
   for (auto *Arg : Args.filtered(OPT_trace_symbol))
     Symtab.trace(Arg->getValue());
 
+  // Initialize Config->PageSize. The default value is defined by the
+  // target, but it can be overriden using the -z common-page-size option.
+  if (Optional<StringRef> Value = getZOptionValue(Args, "common-page-size")) {
+    if (Value->getAsInteger(0, Config->CommonPageSize))
+      error("invalid common page size: " + *Value);
+  } else {
+    Config->CommonPageSize = Target->PageSize;
+  }
+
   // Initialize Config->ImageBase.
   if (auto *Arg = Args.getLastArg(OPT_image_base)) {
     StringRef S = Arg->getValue();
     if (S.getAsInteger(0, Config->ImageBase))
       error(Arg->getSpelling() + ": number expected, but got " + S);
     else if ((Config->ImageBase % Target->PageSize) != 0)
       warning(Arg->getSpelling() + ": address isn't multiple of page size");
   } else {

ELF/LinkerScript.cpp

while (!atEOF() && !Error) {
 
     Lhs = combine(Op1, Lhs, Rhs);
   }
   return Lhs;
 }
 
 uint64_t static getConstant(StringRef S) {
   if (S == "COMMONPAGESIZE")
-    return Target->PageSize;
+    return Config->CommonPageSize;
   if (S == "MAXPAGESIZE")
     return Target->MaxPageSize;
   error("unknown constant: " + S);
   return 0;
 }
 
 // Parses Tok as an integer. Returns true if successful.
 // It recognizes hexadecimal (prefixed with "0x" or suffixed with "H")

test/ELF/linkerscript/zcommon-page-size.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+
+# RUN: echo "SECTIONS { \
+# RUN:         symbol = CONSTANT(COMMONPAGESIZE); \
+# RUN:       }" > %t.script
+# RUN: ld.lld -z common-page-size=0x1234 -o %t1 --script %t.script %t
+# RUN: llvm-objdump -t %t1 | FileCheck %s
+
+# CHECK: 0000000000001234 *ABS* 00000000 symbol
+
+.global _start
+_start:
+ nop