Fangrui Song fbf41b5267 [ELF] Simplify sh_addr computation and warn if sh_addr is not a multiple of sh_addralign
See `docs/ELF/linker_script.rst` for the new computation for sh_addr and sh_addralign.
`ALIGN(section_align)` now means: "increase alignment to section_align"
(like yet another input section requirement).

The "start of section .foo changes from 0x11 to 0x20" warning no longer
makes sense. Change it to warn if sh_addr%sh_addralign!=0.

To decrease the alignment from the default max_input_align,
use `.output ALIGN(8) : {}` instead of `.output : ALIGN(8) {}`
See linkerscript/section-address-align.test as an example.

When both an output section address and ALIGN are set (can be seen as an
"undefined behavior" https://sourceware.org/ml/binutils/2020-03/msg00115.html),
lld may align more than GNU ld, but it makes a linker script working
with GNU ld hard to break with lld.

This patch can be considered as restoring part of the behavior before D74736.

Differential Revision: https://reviews.llvm.org/D75724
2020-03-11 09:35:42 -07:00
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lld Documentation
=================

The lld documentation is written using the Sphinx documentation generator. It is
currently tested with Sphinx 1.1.3.

We currently use the 'nature' theme and a Beaker inspired structure.

See sphinx_intro.rst for more details.