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__DATA -> __DATA_CONST
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Fixes #1
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@mitsuhiko
mitsuhiko committed Jul 2, 2023
1 parent 7973f0b commit 8f0e3b4
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2 changes: 1 addition & 1 deletion Cargo.toml
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
[package]
name = "small_ctor"
version = "0.1.0"
version = "0.1.1"
edition = "2018"
authors = ["Armin Ronacher <armin.ronacher@active-4.com>"]
license = "Apache-2.0"
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2 changes: 1 addition & 1 deletion src/lib.rs
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Expand Up @@ -215,7 +215,7 @@ pub fn ctor(args: TokenStream, input: TokenStream) -> TokenStream {
TokenTree::Punct(Punct::new(',', Spacing::Alone)),
TokenTree::Ident(Ident::new("link_section", Span::call_site())),
TokenTree::Punct(Punct::new('=', Spacing::Alone)),
TokenTree::Literal(Literal::string("__DATA,__mod_init_func")),
TokenTree::Literal(Literal::string("__DATA_CONST,__mod_init_func")),
],
))
],
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4 comments on commit 8f0e3b4

@danakj
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@danakj danakj commented on 8f0e3b4 Jul 20, 2023 •
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I confirm that this change is working in Chromium, where we're linking the rust rlibs with C++ with lld.

It appears that this did not work in the tests you have in this repo though? Does this perhaps need to be configurable depending on the linker choice?

I wonder if the tests there would pass with -Clinker=clang or -Clinker=clang -Clink-arg=-fuse-ld=lld

@danakj
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@danakj danakj commented on 8f0e3b4 Jul 20, 2023

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What relocation model is used when compiling the tests?
https://doc.rust-lang.org/rustc/codegen-options/index.html#relocation-model

I see that when relocation model is static for MachO, LLVM expects to put them in a different place:

void TargetLoweringObjectFileMachO::Initialize(MCContext &Ctx,
                                               const TargetMachine &TM) {
  TargetLoweringObjectFile::Initialize(Ctx, TM);
  if (TM.getRelocationModel() == Reloc::Static) {
    StaticCtorSection = Ctx.getMachOSection("__TEXT", "__constructor", 0,
                                            SectionKind::getData());
    StaticDtorSection = Ctx.getMachOSection("__TEXT", "__destructor", 0,
                                            SectionKind::getData());
  } else {
    StaticCtorSection = Ctx.getMachOSection("__DATA", "__mod_init_func",
                                            MachO::S_MOD_INIT_FUNC_POINTERS,
                                            SectionKind::getData());
    StaticDtorSection = Ctx.getMachOSection("__DATA", "__mod_term_func",
                                            MachO::S_MOD_TERM_FUNC_POINTERS,
                                            SectionKind::getData());
  }

https://github.com/llvm/llvm-project/blob/4b3eaee2701afa2549c9cd0f78692598e9bfd44e/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp#L1191-L1203

FWIW, looking at otool I can see that clang puts C++ static initializers in __DATA_CONST,__mod_term_func, which is not strictly what the code above says, so that must end up modified somehow.

@danakj
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@danakj danakj commented on 8f0e3b4 Jul 21, 2023

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We are investigating more here: https://bugs.chromium.org/p/chromium/issues/detail?id=1466674

@mitsuhiko
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I will look into this now. For some reason when I ran this locally on my machine it passed but apparently it's now failing there too, even for the most basic test of compiling and running the example.

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