Change Details

This implements https://sourceware.org/bugzilla/show_bug.cgi?id=26404#c6 --overwrite-section-script specifies a script which contains several `SECTIONS` commands. Each `SECTIONS` specifies exactly one output section description. The initial syntax is intentionally narrow to facilitate backward compatible extensions in the future. Symbol assignments cannot be used. Not supporting multiple output section descriptions in one `SECTIONS` makes it clear the sections don't have order guarantee. The semantics are similar to `INSERT [BEFORE|AFTER]` in that LinkerScript::hasSectionsCommand is not set, so default linker script rules still apply. In the absence of a main linker script, --overwrite-script can be more convenient than `INSERT` because --overwrite-script does not need a random anchor section used by `INSERT`. 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-section-script` 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 causes a difference when `INSERT` moves one output section more than once. This should not be used in practice (seems that in GNU ld the output sections may just disappear)

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 initial syntax is intentionally narrow to facilitate backward compatible extensions in the future. Symbol assignments cannot be used. OVERWRITE_SECTIONS does not specify a section 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. 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 causes a difference when `INSERT` moves one output section more than once. This 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. This feature does not suppress orphan section placement so a wrong rule can make it easy to shoot oneself in the foot. The traditional `SECTIONS` commands are concatenated so a wrong rule can be more noticeable.

This implements https://sourceware.org/bugzilla/show_bug.cgi?id=26404#c6 --overwrite-section-script specifies a scripAn `OVERWRITE_SECTIONS` command is a `SECTIONS` variant which contains several `SECTIONS` commands. Each `SECTIONS` specifies exactly one output section descriptions. The initial syntax is intentionally narrow to initial syntax is intentionally narrow to facilitate backward compatiblefacilitate backward compatible extensions in the future. Symbol assignments extensions in the future. Symbol assignments cannot be used. Not supporting multiple output section descriptions in one `SECTIONS` makes it clear the sections don't have order guaranteecannot be used. The semantics are similar to `INSERT [BEFORE|AFTER]` in thatOVERWRITE_SECTIONS does not specify a section order. Similar to `INSERT [BEFORE|AFTER]`, `LinkerScript::hasSectionsCommand` is not set, so default linker script rulesso the still apply. In the absence of a main built-in rules (see `docs/ELF/linker _script, --overwrite-script can be.rst`) still apply. `OVERWRITE_SECTIONS` can be more convenient than `INSERT` because --overwrite-scripit does not need a random need an anchor section used by `INSERT`. 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-section-script`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 causes a difference when `INSERT` moves one output section more than once. This 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. This feature does not suppress orphan section placement so a wrong rule can make it easy to shoot oneself in the foot. The traditional `SECTIONS` commands are concatenated so a wrong rule can be more noticeable.