Messages in this thread | | | Date | Tue, 25 Jan 2022 15:58:51 +0000 | From | Mark Rutland <> | Subject | Re: [PATCH v2 0/7] linkage: better symbol aliasing |
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On Tue, Jan 25, 2022 at 04:49:03PM +0100, Ard Biesheuvel wrote: > On Tue, 25 Jan 2022 at 16:46, Mark Rutland <mark.rutland@arm.com> wrote: > > > > On Tue, Jan 25, 2022 at 04:28:11PM +0100, Ard Biesheuvel wrote: > > > On Tue, 25 Jan 2022 at 12:32, Mark Rutland <mark.rutland@arm.com> wrote: > > > > > > > > This series aims to make symbol aliasing simpler and more consistent. > > > > The basic idea is to replace SYM_FUNC_START_ALIAS(alias) and > > > > SYM_FUNC_END_ALIAS(alias) with a new SYM_FUNC_ALIAS(alias, name), so > > > > that e.g. > > > > > > > > SYM_FUNC_START(func) > > > > SYM_FUNC_START_ALIAS(alias1) > > > > SYM_FUNC_START_ALIAS(alias2) > > > > ... asm insns ... > > > > SYM_FUNC_END(func) > > > > SYM_FUNC_END_ALIAS(alias1) > > > > SYM_FUNC_END_ALIAS(alias2) > > > > EXPORT_SYMBOL(alias1) > > > > EXPORT_SYMBOL(alias2) > > > > > > > > ... can become: > > > > > > > > SYM_FUNC_START(name) > > > > ... asm insns ... > > > > SYM_FUNC_END(name) > > > > > > > > SYM_FUNC_ALIAS(alias1, func) > > > > EXPORT_SYMBOL(alias1) > > > > > > > > SYM_FUNC_ALIAS(alias2, func) > > > > EXPORT_SYMBOL(alias2) > > > > > > > > This avoids repetition and hopefully make it easier to ensure > > > > consistency (e.g. so each function has a single canonical name and > > > > associated metadata). > > > > > > > > > > I take it this affects the sizes of the alias ELF symbols? Does that matter? > > > > The alias should be given the same size as the original symbol, unless I've > > made an error. If you look at patch 3: > > > > * In SYM_FUNC_START(name), via SYM_ENTRY_AT(name, ...), we create a local label > > for the start of the function: .L____sym_entry__##name > > > > * In SYM_FUNC_END(name), via SYM_END_AT(name, ...), we create a local label for > > the end of the function: .L____sym_end__##name > > > > * In SYM_FUNC_ALIAS*(alias,name), we define the start and end of the alias as > > the start and end of the original symbol using those local labels, e.g. > > > > | #define SYM_FUNC_ALIAS(alias, name) \ > > | SYM_START_AT(alias, .L____sym_entry__##name, SYM_L_GLOBAL) \ > > | SYM_END_AT(alias, .L____sym_end__##name, SYM_T_FUNC) > > > > Note that: > > > > * SYM_FUNC_START() uses SYM_START(), which uses SYM_ENTRY_AT() > > * SYM_FUNC_END() uses SYM_END(), which uses SYM_END_AT() > > > > ... so the definition of tha alias is ultimately structurally identical to the > > definition of the canoncial name, at least for now. > > > > Ah right, apologies for not looking more carefully - I assumed the > changed placement implied that the aliases had zero size.
NP; I didn't make that clear in the cover letter, and now it's written up and archived for future reference. :)
> And ultimately, I don't think there is an obviously correct answer > anyway, it's just the [apparently non-existent] change in behavior I > was curious about.
FWIW, I hadn't really considered whether we actually need that for the aliases; it was jsut the path of least resistance implementation-wise, and I'd like to be able to use the local labls for the bounds in future for other annotations and sanity-checks.
Thanks, Mark.
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