Re: [Patch,AVR]: Fix PR13697: Wrong symbols with --gc-sections

[Georg-Johann Lay <avr at gjlay dot de>]

Hans-Peter Nilsson schrieb:
> On Tue, 29 May 2012, Georg-Johann Lay wrote:
> > Hans-Peter Nilsson schrieb:
>
> > > Though, adding a symbol should do it, at least for a corrected
> > > linker.
> > You mean adding a symbol to .data by letting the compiler add a symbol
> > in .data for each module?
>
> No, I mean add a symbol in the linker script, like
> ${RELOCATING+ ___data_start_reserved = .) ; }
> (i.e. another one like there is, but without the PROVIDE decoration).

I tried this:

  .data	  : AT (ADDR (.text) + SIZEOF (.text))
  {
     PROVIDE (__data_start = .) ;
    __pr__ = .;
    *(.data)

But with no avail. The map file shows that .data starts at 0x100,
just as without the __pr__, but .bss is wrong and overlaps I/O:

.data           0x00800100        0x0 load address 0x0000009e
                0x00800100                PROVIDE (__data_start, .)
                0x00800100                __pr__ = .
 *(.data)
 *(.data*)
 *(.rodata)
 *(.rodata*)
 *(.gnu.linkonce.d*)
                0x00800100                . = ALIGN (0x2)
                0x00800100                _edata = .
                0x00800100                PROVIDE (__data_end, .)

.bss            0x00800060        0x2
                0x00800060                PROVIDE (__bss_start, .)
 *(.bss)
 .bss           0x00800060        0x2 foo.o
                0x00800060                aaa


At the start of .bss the location counter is moved backwards!
I still think this is a linker bug.

An optimization should never ever change the semantic of a program!