On Thu, Feb 18, 2021 at 01:08:54PM +0100, Jakub Jelinek via Gcc-patches wrote: > On Thu, Feb 18, 2021 at 12:00:59PM +0000, Jozef Lawrynowicz wrote: > > If we can add ".retain <symbol_name>" to GAS, then I agree, current GCC > > SHF_GNU_RETAIN behavior should be removed. For GCC 12 we leverage > > .retain to implement the functionality where "used" saves symbols form > > linker garbage collection, without modifying section names or the > > structure of the object file. > > Even in that case I think it is a bad idea to change the "used" attribute > behavior, not everyone using "used" attribute needs or wants that behavior, > so it should be a functionality provided by a separate new attribute.
I think it is a enhancement, and true to the spirit of the attribute, for "used" to save a symbol from linker garbage collection. Why should "used" mean: Save this symbol from compiler optimization, but allow the linker to remove it. I can't currently think of a use case where a "used" symbol should be kept by the compiler but removed by the linker. Often we see KEEP directives in linker scripts accompanying "used" in the source code. libgcc/crtstuff.c is a good example. GNU linker scripts need many specific KEEP directives to handle all the "used" symbols. If a developer marks a symbol as "used" in the source code, I think the intuitive thing is for that symbol to be present in the linked output file. Jozef
