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SubjectRe: [PATCH] genksyms: Ignore module scoped _Static_assert()
On Tue, Dec 1, 2020 at 7:21 AM Marco Elver <elver@google.com> wrote:
>
> The C11 _Static_assert() keyword may be used at module scope, and we
> need to teach genksyms about it to not abort with an error. We currently
> have a growing number of static_assert() (but also direct usage of
> _Static_assert()) users at module scope:
>
> git grep -E '^_Static_assert\(|^static_assert\(' | grep -v '^tools' | wc -l
> 135
>
> More recently, when enabling CONFIG_MODVERSIONS with CONFIG_KCSAN, we
> observe a number of warnings:
>
> WARNING: modpost: EXPORT symbol "<..all kcsan symbols..>" [vmlinux] [...]
>
> When running a preprocessed source through 'genksyms -w' a number of
> syntax errors point at usage of static_assert()s. In the case of
> kernel/kcsan/encoding.h, new static_assert()s had been introduced which
> used expressions that appear to cause genksyms to not even be able to
> recover from the syntax error gracefully (as it appears was the case
> previously).
>
> Therefore, make genksyms ignore all _Static_assert() and the contained
> expression. With the fix, usage of _Static_assert() no longer cause
> "syntax error" all over the kernel, and the above modpost warnings for
> KCSAN are gone, too.
>
> Signed-off-by: Marco Elver <elver@google.com>

Ah, genksyms...if only there were a library that we could use to parse
C code...:P
Acked-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
> scripts/genksyms/keywords.c | 3 +++
> scripts/genksyms/lex.l | 27 ++++++++++++++++++++++++++-
> scripts/genksyms/parse.y | 7 +++++++
> 3 files changed, 36 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/genksyms/keywords.c b/scripts/genksyms/keywords.c
> index 057c6cabad1d..b85e0979a00c 100644
> --- a/scripts/genksyms/keywords.c
> +++ b/scripts/genksyms/keywords.c
> @@ -32,6 +32,9 @@ static struct resword {
> { "restrict", RESTRICT_KEYW },
> { "asm", ASM_KEYW },
>
> + // c11 keywords that can be used at module scope
> + { "_Static_assert", STATIC_ASSERT_KEYW },
> +
> // attribute commented out in modutils 2.4.2. People are using 'attribute' as a
> // field name which breaks the genksyms parser. It is not a gcc keyword anyway.
> // KAO. },
> diff --git a/scripts/genksyms/lex.l b/scripts/genksyms/lex.l
> index e265c5d96861..ae76472efc43 100644
> --- a/scripts/genksyms/lex.l
> +++ b/scripts/genksyms/lex.l
> @@ -118,7 +118,7 @@ yylex(void)
> {
> static enum {
> ST_NOTSTARTED, ST_NORMAL, ST_ATTRIBUTE, ST_ASM, ST_TYPEOF, ST_TYPEOF_1,
> - ST_BRACKET, ST_BRACE, ST_EXPRESSION,
> + ST_BRACKET, ST_BRACE, ST_EXPRESSION, ST_STATIC_ASSERT,
> ST_TABLE_1, ST_TABLE_2, ST_TABLE_3, ST_TABLE_4,
> ST_TABLE_5, ST_TABLE_6
> } lexstate = ST_NOTSTARTED;
> @@ -201,6 +201,11 @@ repeat:
>
> case EXPORT_SYMBOL_KEYW:
> goto fini;
> +
> + case STATIC_ASSERT_KEYW:
> + lexstate = ST_STATIC_ASSERT;
> + count = 0;
> + goto repeat;
> }
> }
> if (!suppress_type_lookup)
> @@ -401,6 +406,26 @@ repeat:
> }
> break;
>
> + case ST_STATIC_ASSERT:
> + APP;
> + switch (token)
> + {
> + case '(':
> + ++count;
> + goto repeat;
> + case ')':
> + if (--count == 0)
> + {
> + lexstate = ST_NORMAL;
> + token = STATIC_ASSERT_PHRASE;
> + break;
> + }
> + goto repeat;
> + default:
> + goto repeat;
> + }
> + break;
> +
> case ST_TABLE_1:
> goto repeat;
>
> diff --git a/scripts/genksyms/parse.y b/scripts/genksyms/parse.y
> index e22b42245bcc..8e9b5e69e8f0 100644
> --- a/scripts/genksyms/parse.y
> +++ b/scripts/genksyms/parse.y
> @@ -80,6 +80,7 @@ static void record_compound(struct string_list **keyw,
> %token SHORT_KEYW
> %token SIGNED_KEYW
> %token STATIC_KEYW
> +%token STATIC_ASSERT_KEYW
> %token STRUCT_KEYW
> %token TYPEDEF_KEYW
> %token UNION_KEYW
> @@ -97,6 +98,7 @@ static void record_compound(struct string_list **keyw,
> %token BRACE_PHRASE
> %token BRACKET_PHRASE
> %token EXPRESSION_PHRASE
> +%token STATIC_ASSERT_PHRASE
>
> %token CHAR
> %token DOTS
> @@ -130,6 +132,7 @@ declaration1:
> | function_definition
> | asm_definition
> | export_definition
> + | static_assert
> | error ';' { $$ = $2; }
> | error '}' { $$ = $2; }
> ;
> @@ -493,6 +496,10 @@ export_definition:
> { export_symbol((*$3)->string); $$ = $5; }
> ;
>
> +/* Ignore any module scoped _Static_assert(...) */
> +static_assert:
> + STATIC_ASSERT_PHRASE ';' { $$ = $2; }
> + ;
>
> %%
>
> --
> 2.29.2.454.gaff20da3a2-goog
>


--
Thanks,
~Nick Desaulniers

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