[PATCH] D27276: [ELF] Allow defined symbols to be assigned from linker script

[Meador Inge via llvm-commits]

On Mon, Jan 09, 2017 at 02:08:49PM -0500, Rafael Avila de Espindola wrote:

> If there is a '.' in it it should not be ABS. Can you use ABSOLUTE(.) +
> 0x100?

That works.  Thanks!  I will apply that as a work around shortly.

Longer term, we have some bugs around section assignment for
linker-defined symbols.  For example, lld gives:

  $ cat test.ld
  a = 1;
  b = . + 2;
  SECTIONS {
    c = 3;
    .text : {
      *(.text)
      d = 4;
    }
    e = . + 5;
    .data : {
      *(.data)
      f = . + 6;
    }
  }
  $ ./bin/ld.lld -o a.out test.o -T test.ld                                                                                                                                     
  ./bin/ld.lld: warning: cannot find entry symbol _start; defaulting to 0x0
  $ ./bin/llvm-objdump -t a.out
  
  a.out:  file format ELF64-x86-64
  
  SYMBOL TABLE:
  0000000000000000         *UND*           00000000 
  0000000000000001         *ABS*           00000000 a
  0000000000000000 g     F .text           00000000 foo
  0000000000000002         .text           00000000 b
  0000000000000003         *ABS*           00000000 c
  0000000000000004         *ABS*           00000000 d
  000000000000000d         .text           00000000 e
  0000000000000012         .data           00000000 f

GNU ld, gives:

  $ ld -o a.out test.o -T test.ld
  $ ./bin/llvm-objdump -t a.out
  
  a.out:  file format ELF64-x86-64
  
  SYMBOL TABLE:
  0000000000000000         *UND*           00000000 
  0000000000000000 l    d  .text           00000000 .text
  0000000000000008 l    d  .data           00000000 .data
  0000000000000000 l    df *ABS*           00000000 test.c
  0000000000000000 l    df *ABS*           00000000 
  0000000000000002         *ABS*           00000000 b
  0000000000000012         .data           00000000 f
  0000000000000003         *ABS*           00000000 c
  0000000000000004         .text           00000000 d
  0000000000000000 g     F .text           00000000 foo
  0000000000000001 g       *ABS*           00000000 a
  000000000000000d         *ABS*           00000000 e

A few observations from the above:

  1. Symbols defined *inside* output section descriptors should live in
     that section (e.g. `d`, `f`).

  2. Symbols defined *outside* output section descriptors should be *ABS*
     (e.g. `a`, `b`, `c`, and `e`).

Cheers,

-- 
Meador Inge
meadori at codesourcery.com
CodeSourcery / Mentor Embedded