gccrs: Implement C-style string literals by Polygonalr · Pull Request #4565 · Rust-GCC/gccrs

Polygonalr · 2026-05-31T14:35:06Z

This is not part of Rust 1.49, but it's nice to backport it for now, since Rust for Linux uses C-style string literals a bit.

Current behaviour is similar to normal string literals, except they are type-checked as slice types instead of array, and the compiled fat pointer has +1 to size to include the null terminator.

CohenArthur

I think the code is really good, but I'd like to have a think about that resulting &CStr type vs [u8] type before we merge it. Can you please check that as soon as C-style string literals were added, CStr became a lang item, in which case we should be able to refer to it within the typechecker and use that type, and if so, we have to figure out a way to get to the CStr type with a 1.49 libcore which does not have the CStr as a lang item yet

CohenArthur · 2026-06-02T13:34:48Z

+      // C-style strings
+      else if (current_char == 'c' && peek_input () == '"')
+	return parse_c_string (loc);


Note that in a later PR you can also add C-style raw strings the same way, but I don't know if the kernel makes use of those

dkm · 2026-06-07T09:49:52Z

FWIW, the changelog is not correct. You need to follow the * file.ext (item): What changed pattern.
Please do not simply point at the file :) See for example:

gcc/rust/ChangeLog:
	* lex/rust-token.h: Add C_STRING_LITERAL and RAW_C_STRING_LITERAL (unused
	for now).
	* lex/rust-lex.h: Define new parse_c_string function.
	* lex/rust-lex.cc: Implement lexing for C-style string literals.
	* hir/tree/rust-hir-literal.h: Define new C_STRING LitType.

Can you do some cleanup there? Thanks!

Polygonalr · 2026-06-08T01:22:07Z

FWIW, the changelog is not correct. You need to follow the * file.ext (item): What changed pattern. Please do not simply point at the file :) See for example:
gcc/rust/ChangeLog:
	* lex/rust-token.h: Add C_STRING_LITERAL and RAW_C_STRING_LITERAL (unused
	for now).
	* lex/rust-lex.h: Define new parse_c_string function.
	* lex/rust-lex.cc: Implement lexing for C-style string literals.
	* hir/tree/rust-hir-literal.h: Define new C_STRING LitType.
Can you do some cleanup there? Thanks!

@dkm Just did some commit message clean-up, apologies for not being specific enough in my commit messages 😓, I'll do my best not to repeat this in the future.

CohenArthur

Good work @Polygonalr :) well done

CohenArthur · 2026-06-08T15:03:02Z

+  // +1 for null terminator, unlike Rust string literals.
+  tree size = build_int_cstu (type, literal_value.as_string ().size () + 1);


This is correct, but don't we also need to add an extra zero byte at the end?

Is it taken care of by the backend already?

C++11 strings already come with a null terminator, so I don't think we need to handle it.

CohenArthur

LGTM, sorry for the nitpick :)

CohenArthur

Please add an execute test to ensure that the last character in the CStr is indeed a zero byte. Something like this:

fn main() -> i32 {
   let a = c"something";
   
   last_byte(a) as i32
}

Current behaviour is similar to normal string literals, except they are type-checked as slice types instead of array, and the compiled fat pointer has +1 to size to include the null terminator. gcc/rust/ChangeLog: * lex/rust-token.h (RS_TOKEN_LIST): Add C_STRING_LITERAL and RAW_C_STRING_LITERAL (unused for now). * lex/rust-lex.h (Lexer): Define new parse_c_string function. * lex/rust-lex.cc (Lexer::build_token): Implement lexing for C-style string literals. (Lexer::parse_c_string): Add implementation. * hir/tree/rust-hir-literal.h (HIR::Literal): Define new C_STRING LitType. * hir/rust-ast-lower-base.cc (ASTLoweringBase::lower_literal): Add new case for C_STRING. * parse/rust-parse-impl-attribute.hxx (Parser<ManagedTokenSource>::parse_attr_input): Add new case for C_STRING. * parse/rust-parse-impl-expr.hxx (Parser<ManagedTokenSource>::parse_literal_expr): Add new case for parsing C_STRING. (Parser<ManagedTokenSource>::null_denotation_not_path): Add new case for C_STRING. * ast/rust-ast.h (Token::is_string_lit): Add new case for C_STRING_LITERAL. * ast/rust-ast.cc (AttributeParser::parse_meta_item_inner): Add new case for C_STRING_LITERAL. * ast/rust-ast-collector.cc (TokenCollector::visit): Add new case for C_STRING_LITERAL. * typecheck/rust-hir-type-check-base.cc (TypeCheckBase::resolve_literal): Implement type checking for the new C_STRING type. * backend/rust-compile-expr.h (CompileExpr): Define new function compile_c_string_literal. * backend/rust-compile-expr.cc (CompileExpr::visit(LiteralExpr)): Add new case for C_STRING. (CompileExpr::compile_c_string_literal): Implement compilation of C-style string literals. Signed-off-by: Yap Zhi Heng <yapzhhg@gmail.com>

…iterals gcc/rust/ChangeLog: * lang.opt: Add new -frust-c-style-string-literals option. * parse/rust-parse.h: Import options.h for reading flag_c_style_string_literals. * parse/rust-parse-impl-expr.hxx (Parser<ManagedTokenSource>::parse_literal_expr): Abort parsing C-style string literals if flag_c_style_string_literals is not set. (Parser<ManagedTokenSource>::null_denotation_not_path): Ditto. gcc/testsuite/ChangeLog: * rust/execute/torture/c_string.rs: Set -frust-c-style-string-literals. * rust/compile/c_string_null_byte_check.rs: Set -frust-c-style-string-literals. Signed-off-by: Yap Zhi Heng <yapzhhg@gmail.com>

gcc/rust/ChangeLog: * util/rust-lang-item.h (LangItem::Kind): New CSTR kind. * util/rust-lang-item.cc (LangItem::lang_items): Ditto. * backend/rust-compile-type.cc (visit(TyTy::ReferenceType)): Add specific record type for CStr. * typecheck/rust-tyty.h (ReferenceType): Add function definition for is_dyn_cstr_type. * typecheck/rust-tyty.cc (ReferenceType::is_dyn_object): Update to include is_dyn_cstr_type. (ReferenceType::is_dyn_cstr_type): Add implementation to check whether the ReferenceType is of type CStr. * typecheck/rust-hir-type-check-base.cc(resolve_literal): Update C_STRING case to resolve to the CStr language item instead. gcc/testsuite/ChangeLog: * rust/execute/torture/c_string.rs: Add CStr language item definition. * rust/compile/c_string_null_byte_check.rs: Ditto. * rust/execute/torture/c_string_ensure_null_term.rs: New test. Signed-Off-By: Yap Zhi Heng <yapzhhg@gmail.com>

gcc/rust/ChangeLog: * backend/rust-compile-expr.cc (CompileExpr::visit (FieldAccessExpr)): Handle DST fat pointers by reinterpreting the fat pointer as its field type. Signed-Off-By: Yap Zhi Heng <yapzhhg@gmail.com>

Polygonalr force-pushed the c-str branch 6 times, most recently from d3a37b6 to 9d8970b Compare June 2, 2026 13:12

Polygonalr changed the title ~~gccrs: Implement C-style strings~~ gccrs: Implement C-style string literals Jun 2, 2026

CohenArthur reviewed Jun 2, 2026

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Polygonalr marked this pull request as draft June 3, 2026 01:08

Polygonalr force-pushed the c-str branch 4 times, most recently from 43cf3e8 to 5098778 Compare June 8, 2026 01:20

Polygonalr force-pushed the c-str branch from 5098778 to 79dff8d Compare June 8, 2026 01:23

Polygonalr marked this pull request as ready for review June 8, 2026 01:25

CohenArthur reviewed Jun 8, 2026

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CohenArthur added the rust-for-linux Issue related to the compilation of the Linux kernel and its crates label Jun 11, 2026

Polygonalr force-pushed the c-str branch 4 times, most recently from e539e9e to 8e33e90 Compare June 12, 2026 06:37

CohenArthur approved these changes Jun 15, 2026

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Comment thread gcc/rust/backend/rust-compile-type.cc Outdated

CohenArthur reviewed Jun 15, 2026

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Polygonalr force-pushed the c-str branch 2 times, most recently from 896c8f8 to 6b77f3f Compare June 18, 2026 15:20

Polygonalr added 3 commits June 21, 2026 16:04

Polygonalr marked this pull request as draft June 22, 2026 13:20

gccrs: Fix field access on DST fat pointers

116673c

gcc/rust/ChangeLog: * backend/rust-compile-expr.cc (CompileExpr::visit (FieldAccessExpr)): Handle DST fat pointers by reinterpreting the fat pointer as its field type. Signed-Off-By: Yap Zhi Heng <yapzhhg@gmail.com>

Polygonalr force-pushed the c-str branch from 6b77f3f to 116673c Compare June 23, 2026 14:41

Polygonalr marked this pull request as ready for review June 23, 2026 14:54

		// +1 for null terminator, unlike Rust string literals.
		tree size = build_int_cstu (type, literal_value.as_string ().size () + 1);

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dkm commented Jun 7, 2026

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Polygonalr commented May 31, 2026 •

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