Linker script, start address of "subsection" and alignment

[Mike Hommey <mh at glandium dot org>]

Hi,

Consider the following C source:

```
__attribute__((aligned(32), section(".foo")))
long foo = 0;
```

And the following linker script:
```
SECTIONS {
    .data : {
        __foo = .;
        *(.foo)
    }
}
```

The goal being to have the `__foo` symbol point at the first thing that
was originally in the `.foo` section.

But this doesn't actually work because of the alignment. That is, `__foo`
gets its value pre-alignment. This is what -print-map says about .data:

```
.data           0x0000000000201020       0x28
 *(.data .data.* .gnu.linkonce.d.*)
 .data          0x0000000000201020        0x0 /usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/crti.o
 .data          0x0000000000201020        0x0 /usr/lib/gcc/x86_64-linux-gnu/7/crtbeginS.o
 .data.rel.local
                0x0000000000201020        0x8 /usr/lib/gcc/x86_64-linux-gnu/7/crtbeginS.o
                0x0000000000201020                __dso_handle
 .data          0x0000000000201028        0x0 /tmp/ccEGZYAm.o
 .data          0x0000000000201028        0x0 /usr/lib/gcc/x86_64-linux-gnu/7/crtendS.o
 .data          0x0000000000201028        0x0 /usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/crtn.o
                0x0000000000201028                __foo = .
 *(.foo)
 *fill*         0x0000000000201028       0x18 
 .foo           0x0000000000201040        0x8 /tmp/ccEGZYAm.o
                0x0000000000201040                foo
```

It is somehow possible to align by adding the following before the
symbol assignment in the linker script:
```
. = ALIGN(32)
```

but that doesn't seem very satisfactory. ALIGNOF doesn't allow to get
the alignment requirement from some input. Am I missing something or
is it not possible to do this "generically"?

Mike