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Limit symbols exported from proc macros #99944

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Merged
merged 3 commits into from
Aug 1, 2022
Merged

Limit symbols exported from proc macros #99944

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6098e79
Limit symbols exported from proc macros
bjorn3 Jul 30, 2022
df13721
Remove workarounds for issue 59998
bjorn3 Jul 31, 2022
b87f8a4
Add issue reference
bjorn3 Jul 31, 2022
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4 changes: 1 addition & 3 deletions compiler/rustc_codegen_ssa/src/back/linker.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -656,9 +656,7 @@ impl<'a> Linker for GccLinker<'a> {
return;
}

if crate_type == CrateType::ProcMacro {
return;
}
// FIXME hide #[no_mangle] symbols for proc-macros

let is_windows = self.sess.target.is_like_windows;
let path = tmpdir.join(if is_windows { "list.def" } else { "list" });
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8 changes: 5 additions & 3 deletions compiler/rustc_codegen_ssa/src/back/symbol_export.rs
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Expand Up @@ -257,16 +257,18 @@ fn exported_symbols_provider_local<'tcx>(
}));
}

if tcx.sess.crate_types().contains(&CrateType::Dylib) {
if tcx.sess.crate_types().contains(&CrateType::Dylib)
|| tcx.sess.crate_types().contains(&CrateType::ProcMacro)
{
let symbol_name = metadata_symbol_name(tcx);
let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));

symbols.push((
exported_symbol,
SymbolExportInfo {
level: SymbolExportLevel::Rust,
level: SymbolExportLevel::C,
kind: SymbolExportKind::Data,
used: false,
used: true,
Comment on lines -260 to +271
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cc @michaelwoerister @wesleywiser @rust-lang/wg-llvm
Is anyone aware of any potential negative consequences of this?

I'm a bit surprised we even need a symbol (and don't find it by section instead).

If the symbol only exists to keep the section from being GC'd, shouldn't it be some form of unexported #[used]? (e.g. keep Rust export level, or go even lower? but always set used: true)

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@bjorn3 bjorn3 Jul 30, 2022 •
edited
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The symbol is needed on at least macOS to prevent the section from being discarded. The exact name is unique. I think it would make sense in the future to ensure that the symbol exists when using a dylib as dependency to ensure versions don't get mixed without recompilation.

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@eddyb eddyb Jul 31, 2022 •
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Heh, right, the SVH enforcement ideas, but is this symbol accessible to the dynamic loader at all?
Also it might be good to have dedicated symbols in case the metadata ones get stripped.

EDIT: moved the rest of the comment below to #73917 (comment)

(click to open old version)

We could even have something like this:

struct LinkGuard {
    deps: &'static [&'static LinkGuard],
}

extern "Rust" {
    // foo[b7924b40b7ed5e7f]::{shim:LINK_GUARD#0}::<0x461e83de35f0b704f7e69b4cc741ad8eu128>
    #[link_name = "_RINSCsfL95rG4I7iB_3foo10LINK_GUARDKo461e83de35f0b704f7e69b4cc741ad8e_E"] 
    static LINK_GUARD_DEP_FOO: LinkGuard;

    // bar[acb4b2d152c0bd2e]::{shim:LINK_GUARD#0}::<0xf8fc0fadc6a6e727eef4b916531abfe9u128>
    #[link_name = "_RINSCsePjaApBJGQA_3bar10LINK_GUARDKof8fc0fadc6a6e727eef4b916531abfe9_E"] 
    static LINK_GUARD_DEP_BAR: LinkGuard;
}

// my_crate[78009e3fbfa2f6af]::{shim:LINK_GUARD#0}::<0xe538955c5950b59a598304a1e701c9fbu128>
#[export_name = "_RINSCsaiLK1vfX74x_8my_crate10LINK_GUARDKoe538955c5950b59a598304a1e701c9fb_E"]
pub static LINK_GUARD: LinkGuard {
    deps: unsafe { &[
        &LINK_GUARD_DEP_FOO,
        &LINK_GUARD_DEP_BAR,
    ] }
};

(and then use global constructors to ensure it gets kept in - potentially even doing some redundant SVH checking at runtime too...? or something more cursed where it's "activating" something that would be broken otherwise. but that's too much)

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That makes sense. cc #73917

},
));
}
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21 changes: 21 additions & 0 deletions src/test/run-make-fulldeps/symbol-visibility/Makefile
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Expand Up @@ -5,13 +5,15 @@ include ../tools.mk
NM=nm -D
CDYLIB_NAME=liba_cdylib.so
RDYLIB_NAME=liba_rust_dylib.so
PROC_MACRO_NAME=liba_proc_macro.so
EXE_NAME=an_executable
COMBINED_CDYLIB_NAME=libcombined_rlib_dylib.so

ifeq ($(UNAME),Darwin)
NM=nm -gU
CDYLIB_NAME=liba_cdylib.dylib
RDYLIB_NAME=liba_rust_dylib.dylib
PROC_MACRO_NAME=liba_proc_macro.dylib
EXE_NAME=an_executable
COMBINED_CDYLIB_NAME=libcombined_rlib_dylib.dylib
endif
Expand All @@ -20,6 +22,7 @@ ifdef IS_WINDOWS
NM=nm -g
CDYLIB_NAME=liba_cdylib.dll.a
RDYLIB_NAME=liba_rust_dylib.dll.a
PROC_MACRO_NAME=liba_proc_macro.dll
EXE_NAME=an_executable.exe
COMBINED_CDYLIB_NAME=libcombined_rlib_dylib.dll.a
endif
Expand All @@ -31,6 +34,7 @@ all:
$(RUSTC) -Zshare-generics=no an_rlib.rs
$(RUSTC) -Zshare-generics=no a_cdylib.rs
$(RUSTC) -Zshare-generics=no a_rust_dylib.rs
$(RUSTC) -Zshare-generics=no a_proc_macro.rs
$(RUSTC) -Zshare-generics=no an_executable.rs
$(RUSTC) -Zshare-generics=no a_cdylib.rs --crate-name combined_rlib_dylib --crate-type=rlib,cdylib

Expand All @@ -54,6 +58,14 @@ all:
# Check that a Rust dylib does not export generics if -Zshare-generics=no
[ "$$($(NM) $(TMPDIR)/$(RDYLIB_NAME) | grep -v __imp_ | grep -c public_generic_function_from_rlib)" -eq "0" ]

# Check that a proc macro exports its public #[no_mangle] functions
# FIXME avoid exporting #[no_mangle] symbols for proc macros
[ "$$($(NM) $(TMPDIR)/$(CDYLIB_NAME) | grep -v __imp_ | grep -c public_c_function_from_cdylib)" -eq "1" ]
# Check that a proc macro exports the public #[no_mangle] functions of dependencies
[ "$$($(NM) $(TMPDIR)/$(CDYLIB_NAME) | grep -v __imp_ | grep -c public_c_function_from_rlib)" -eq "1" ]
# Check that a proc macro DOES NOT export any public Rust functions
[ "$$($(NM) $(TMPDIR)/$(CDYLIB_NAME) | grep -v __imp_ | grep -c $(RE_ANY_RUST_SYMBOL))" -eq "0" ]

# FIXME(nbdd0121): This is broken in MinGW, see https://github.com/rust-lang/rust/pull/95604#issuecomment-1101564032
ifndef IS_WINDOWS
# Check that an executable does not export any dynamic symbols
Expand All @@ -75,6 +87,7 @@ endif
$(RUSTC) -Zshare-generics=yes an_rlib.rs
$(RUSTC) -Zshare-generics=yes a_cdylib.rs
$(RUSTC) -Zshare-generics=yes a_rust_dylib.rs
$(RUSTC) -Zshare-generics=yes a_proc_macro.rs
$(RUSTC) -Zshare-generics=yes an_executable.rs

# Check that a cdylib exports its public #[no_mangle] functions
Expand All @@ -94,6 +107,14 @@ endif
[ "$$($(NM) $(TMPDIR)/$(RDYLIB_NAME) | grep -v __imp_ | grep -c public_rust_function_from_rlib)" -eq "1" ]
[ "$$($(NM) $(TMPDIR)/$(RDYLIB_NAME) | grep -v __imp_ | grep -c public_generic_function_from_rlib)" -eq "1" ]

# Check that a proc macro exports its public #[no_mangle] functions
# FIXME avoid exporting #[no_mangle] symbols for proc macros
[ "$$($(NM) $(TMPDIR)/$(CDYLIB_NAME) | grep -v __imp_ | grep -c public_c_function_from_cdylib)" -eq "1" ]
# Check that a proc macro exports the public #[no_mangle] functions of dependencies
[ "$$($(NM) $(TMPDIR)/$(CDYLIB_NAME) | grep -v __imp_ | grep -c public_c_function_from_rlib)" -eq "1" ]
# Check that a proc macro DOES NOT export any public Rust functions
[ "$$($(NM) $(TMPDIR)/$(CDYLIB_NAME) | grep -v __imp_ | grep -c $(RE_ANY_RUST_SYMBOL))" -eq "0" ]

ifndef IS_WINDOWS
# Check that an executable does not export any dynamic symbols
[ "$$($(NM) $(TMPDIR)/$(EXE_NAME) | grep -v __imp_ | grep -c public_c_function_from_rlib)" -eq "0" ]
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9 changes: 9 additions & 0 deletions src/test/run-make-fulldeps/symbol-visibility/a_proc_macro.rs
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@@ -0,0 +1,9 @@
#![crate_type = "proc-macro"]

extern crate an_rlib;

// This should not be exported
#[no_mangle]
extern "C" fn public_c_function_from_cdylib() {
an_rlib::public_c_function_from_rlib();
}