[llvm-dev] [libLTO] accessing llvm.global_ctors

[Fāng-ruì Sòng via llvm-dev]

On Mon, Jul 26, 2021 at 3:40 PM Wael Yehia <wyehia at ca.ibm.com> wrote:

> -----"Steven Wu" <stevenwu at apple.com> wrote: -----
> To: "Wael Yehia" <wyehia at ca.ibm.com>
> From: "Steven Wu" <stevenwu at apple.com>
> Date: 07/26/2021 04:03PM
> Cc: "Fangrui Song" <maskray at google.com>, "LLVM-DEV LIST" <
> llvm-dev at lists.llvm.org>
> Subject: [EXTERNAL] Re: [llvm-dev] [libLTO] accessing llvm.global_ctors
>
>
> >> On Jul 26, 2021, at 10:59 AM, Wael Yehia <wyehia at ca.ibm.com> wrote:
> >>
> >>
> >>
> >>
> >> -----"Steven Wu" <stevenwu at apple.com> wrote: -----
> >> To: "Wael Yehia" <wyehia at ca.ibm.com>
> >> From: "Steven Wu" <stevenwu at apple.com>
> >> Date: 07/26/2021 12:22PM
> >> Cc: "Fangrui Song" <maskray at google.com>, llvm-dev at lists.llvm.org
> >> Subject: [EXTERNAL] Re: [llvm-dev] [libLTO] accessing llvm.global_ctors
> >>
> >>> It also sounds like that you just need to know if the object file has
> constructor or not, but don't really care anything more than that?
> >> yes
> >>
> >>
> >>> Can you read the section name from the IRSymtab to figure out if that
> is a constructor/destructor or not?
> >> Is this a suggestion of how to implement the query I'm after?
> >> My initial thought was to simply check for the presence of the symbols
> `llvm.global_ctors` and `llvm.global_dtors` in the ModuleSymbolTable in the
> LTOModule.
> >
> >The reason why I don't want to do that is because they are not real
> symbols and linker do not know how to resolve them. You could stamp a
> different attribute on them but the old linker will not be able to
> understand them.
>
> Just to be clear, i'm not proposing that these two symbols start being
> accessible through the
> `lto_module_get_[num_symbols|symbol_name|symbol_attribute]` functions
> (which would make them visible to a linker).
> I'm proposing something like:
>
> lto_bool_t lto_module_has_ctor_dtor(lto_module_t mod) {
>   return unwrap(mod)->hasCtorDtor();
> }
>
> bool LTOModule::hasCtorDtor() {
>    // either (1) traverse `ModuleSymbolTable SymTab` or
>    // (2) compute and cache the answer when LTOModule::parseSymbols runs
> }
>
>
Do we need a new lto-c API? Can something like LLVMGetNamedGlobal be used?
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