[PATCH] [lld][ELF] Add static TLS support.

[Sean Silva]

================
Comment at: lib/ReaderWriter/ELF/DefaultLayout.h:75-76
@@ -74,2 +74,4 @@
     ORDER_BSS = 210,
+    ORDER_TLSDATA = 215,
+    ORDER_TLSBSS = 216,
     ORDER_OTHER = 220,
----------------
Michael Spencer wrote:
> Shankar Kalpathi Easwaran wrote:
> > I see that gnu ld / gold puts .tdata/.tbss before .data, why are you ordering it differently ?
> > 
> > $cat t.c
> > __thread int a = 10;
> > __thread int b = 20;
> > __thread int f;
> > __thread int g;
> > int initdata = 10;
> > int bssdata;
> > 
> > int main()
> > {
> >   return 0;
> > }
> > 
> > $gcc -c t.c
> > $gold t.o
> > $readelf -S a.out
> > There are 12 section headers, starting at offset 0x2ac:
> > 
> > Section Headers:
> >   [Nr] Name              Type            Addr     Off    Size   ES Flg Lk Inf Al
> >   [ 0]                   NULL            00000000 000000 000000 00      0   0  0
> >   [ 1] .text             PROGBITS        080480b4 0000b4 00000a 00  AX  0   0  4
> >   [ 2] .eh_frame         PROGBITS        080480c0 0000c0 000038 00   A  0   0  4
> >   [ 3] .tdata            PROGBITS        080490f8 0000f8 000008 00 WAT  0   0  4
> >   [ 4] .tbss             NOBITS          08049100 000100 000008 00 WAT  0   0  4
> >   [ 5] .data             PROGBITS        08049100 000100 000004 00  WA  0   0  4
> >   [ 6] .bss              NOBITS          08049104 000104 000004 00  WA  0   0  4
> >   [ 7] .comment          PROGBITS        00000000 000104 00002b 01  MS  0   0  1
> >   [ 8] .note.gnu.gold-ve NOTE            00000000 000130 00001c 00      0   0  4
> >   [ 9] .symtab           SYMTAB          00000000 00014c 0000c0 10     10   2  4
> >   [10] .strtab           STRTAB          00000000 00020c 00003b 00      0   0  1
> >   [11] .shstrtab         STRTAB          00000000 000247 000063 00      0   0  1
> > Key to Flags:
> >   W (write), A (alloc), X (execute), M (merge), S (strings)
> >   I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)
> >   O (extra OS processing required) o (OS specific), p (processor specific)
> > 
> I'll fix. I see how they are handling it now. Note that they are still going to get separate LOAD segments currently because we don't have a way to say that .tbss should be ignored in the LOAD segment, but not the TLS segment.
> I see how they are handling it now.

If you are seeing these things by experimenting with their behavior, you can instead just read it off the relevant default linker script in `/usr/lib/ldscripts/`. E.g. for the default ldscript for x86_64 ELF executables on my machine (`elf_x86_64.x`), you can just read off:

```
  .tdata	  : { *(.tdata .tdata.* .gnu.linkonce.td.*) }
  .tbss		  : { *(.tbss .tbss.* .gnu.linkonce.tb.*) *(.tcommon) }
[...snip...]
  .data           :
  {
    *(.data .data.* .gnu.linkonce.d.*)
    SORT(CONSTRUCTORS)
  }
```


http://llvm-reviews.chandlerc.com/D351