[llvm][ELF] Add ELF header/section header table size statistics (#109345)

Followup to #102363. This makes the `elf-object-writer.*Bytes` stats sum
up to `assembler.ObjectBytes`.

Author: aeubanks

llvm/lib/MC/ELFObjectWriter.cpp

@@ -68,6 +68,8 @@ using namespace llvm;
 namespace {
 namespace stats {
 
+STATISTIC(ELFHeaderBytes, "Total size of ELF headers");
+STATISTIC(SectionHeaderBytes, "Total size of section headers table");
 STATISTIC(AllocTextBytes, "Total size of SHF_ALLOC text sections");
 STATISTIC(AllocROBytes, "Total size of SHF_ALLOC readonly sections");
 STATISTIC(AllocRWBytes, "Total size of SHF_ALLOC read-write sections");
@@ -945,6 +947,7 @@ void ELFWriter::writeSectionHeader(uint32_t GroupSymbolIndex, uint64_t Offset,
 }
 
 void ELFWriter::writeSectionHeaders(const MCAssembler &Asm) {
+  uint64_t Start = W.OS.tell();
   const unsigned NumSections = SectionTable.size();
 
   // Null section first.
@@ -1008,6 +1011,8 @@ void ELFWriter::writeSectionHeaders(const MCAssembler &Asm) {
 
     writeSectionHeader(GroupSymbolIndex, Offsets.first, Size, *Section);
   }
+
+  stats::SectionHeaderBytes += W.OS.tell() - Start;
 }
 
 uint64_t ELFWriter::writeObject(MCAssembler &Asm) {
@@ -1023,6 +1028,8 @@ uint64_t ELFWriter::writeObject(MCAssembler &Asm) {
   // Write out the ELF header ...
   writeHeader(Asm);
 
+  stats::ELFHeaderBytes += W.OS.tell() - StartOffset;
+
   // ... then the sections ...
   SmallVector<std::pair<MCSectionELF *, SmallVector<unsigned>>, 0> Groups;
   // Map from group section index to group

llvm/test/CodeGen/X86/section-stats.ll

@@ -3,6 +3,8 @@
 
 ; CHECK-DAG: 1 elf-object-writer - Total size of SHF_ALLOC text sections
 ; CHECK-DAG: 1 elf-object-writer - Total size of SHF_ALLOC read-write sections
+; CHECK-DAG: 512 elf-object-writer - Total size of section headers table
+; CHECK-DAG: 64 elf-object-writer - Total size of ELF headers
 
 target triple = "x86_64-unknown-linux-gnu"