Re: [PATCH v1 3/3] kallsyms: increase maximum kernel symbol length to 512

Geert Stappers
2022-05-06T09:56:06Z

On Thu, May 05, 2022 at 09:16:45PM +0200, Miguel Ojeda wrote:
>
> generates a symbol of length 96 when using the upcoming v0 mangling scheme:
>
> _RNvXNtCshGpAVYOtgW1_7example9my_moduleINtB2_13MyGenericTypeNtB2_6MyTypeENtB2_7MyTrait9my_method
>
> At the moment, Rust symbols may reach up to 300 in length.
> Setting 512 as the maximum seems like a reasonable choice to
> keep some headroom.
>
> diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
> index ce1bd2fbf23e..e5ad6e31697d 100644
> --- a/include/linux/kallsyms.h
> +++ b/include/linux/kallsyms.h
> @@ -15,7 +15,7 @@
>
> #include <asm/sections.h>
>
> -#define KSYM_NAME_LEN 128
> +#define KSYM_NAME_LEN 512

multiplication factor is four

> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -213,7 +213,7 @@ static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab,
> * we use the smallest/strictest upper bound possible (56, based on
> * the current definition of MODULE_NAME_LEN) to prevent overflows.
> */
> - BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 128);
> + BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 512);

factor four

> @@ -227,7 +227,7 @@ static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab,
>
> /* Format: .klp.sym.sym_objname.sym_name,sympos */
> cnt = sscanf(strtab + sym->st_name,
> - ".klp.sym.%55[^.].%127[^,],%lu",
> + ".klp.sym.%55[^.].%511[^,],%lu",

4 * ( 127 + 1 ) = 511 + 1

> --- a/scripts/kallsyms.c
> +++ b/scripts/kallsyms.c
> @@ -30,10 +30,10 @@
> #define _stringify_1(x) #x
> #define _stringify(x) _stringify_1(x)
>
> -#define KSYM_NAME_LEN 128
> +#define KSYM_NAME_LEN 512

factor four

> --- a/tools/include/linux/kallsyms.h
> +++ b/tools/include/linux/kallsyms.h
> @@ -6,7 +6,7 @@
> #include <stdio.h>
> #include <unistd.h>
>
> -#define KSYM_NAME_LEN 128
> +#define KSYM_NAME_LEN 512

factor four

> --- a/tools/lib/perf/include/perf/event.h
> +++ b/tools/lib/perf/include/perf/event.h
> @@ -95,7 +95,7 @@ struct perf_record_throttle {
> };
>
> #ifndef KSYM_NAME_LEN
> -#define KSYM_NAME_LEN 256
> +#define KSYM_NAME_LEN 512

Here is the multiplication factor two.

> --- a/tools/lib/symbol/kallsyms.h
> +++ b/tools/lib/symbol/kallsyms.h
> @@ -7,7 +7,7 @@
> #include <linux/types.h>
>
> #ifndef KSYM_NAME_LEN
> -#define KSYM_NAME_LEN 256
> +#define KSYM_NAME_LEN 512

Another "factor two"

It feels good to unify all the KSYM_NAME_LEN to 512.

Thing that feels less good is doubling 256 versus quadrupling 128.

I felt the need to report that.

Feel free to ignore this remark.

Groeten
Geert Stappers
--
Silence is hard to parse