Fangrui Song 899fdf548e [ELF] Add OVERWRITE_SECTIONS command ... This implements https://sourceware.org/bugzilla/show_bug.cgi?id=26404 An `OVERWRITE_SECTIONS` command is a `SECTIONS` variant which contains several output section descriptions. The output sections do not have specify an order. Similar to `INSERT [BEFORE|AFTER]`, `LinkerScript::hasSectionsCommand` is not set, so the built-in rules (see `docs/ELF/linker_script.rst`) still apply. `OVERWRITE_SECTIONS` can be more convenient than `INSERT` because it does not need an anchor section. The initial syntax is intentionally narrow to facilitate backward compatible extensions in the future. Symbol assignments cannot be used. This feature is versatile. To list a few usage: * Use `section : { KEEP(...) }` to retain input sections under GC * Define encapsulation symbols (start/end) for an output section * Use `section : ALIGN(...) : { ... }` to overalign an output section (similar to ld64 `-sectalign`) When an output section is specified by both `OVERWRITE_SECTIONS` and `INSERT`, `INSERT` is processed after overwrite sections. To make this work, this patch changes `InsertCommand` to use name based matching instead of pointer based matching. (This may cause a difference when `INSERT` moves one output section more than once. Such duplicate commands should not be used in practice (seems that in GNU ld the output sections may just disappear).) A linker script can be used without -T/--script. The traditional `SECTIONS` commands are concatenated, so a wrong rule can be more noticeable from the section order. This feature if misused can be less noticeable, just like `INSERT`. Differential Revision: https://reviews.llvm.org/D103303		2021-06-13 12:41:11 -07:00
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linker_script.rst	[ELF] Add OVERWRITE_SECTIONS command	2021-06-13 12:41:11 -07:00
warn_backrefs.rst	[ELF][docs] Add line breaks	2021-03-22 16:08:47 +08:00