On Thu, Mar 12, 2020 at 5:37 AM Mikhail Petrov <Mikhail.Petrov@xxxxxxx> wrote:
>
> There is the code in the read_symbol function in 'scripts/kallsyms.c':
>
> if (is_ignored_symbol(name, type))
> return NULL;
>
> /* Ignore most absolute/undefined (?) symbols. */
> if (strcmp(name, "_text") == 0)
> _text = addr;
>
> But the is_ignored_symbol function returns true for name="_text" and
> type='A'. So the next condition is not executed and the _text variable
> is always zero.
>
> It makes the wrong kallsyms_relative_base symbol as a result of the code
> (CONFIG_KALLSYMS_BASE_RELATIVE is defined):
>
> if (base_relative) {
> output_label("kallsyms_relative_base");
> output_address(relative_base);
> printf("\n");
> }
>
> Because the output_address function uses the _text variable.
>
> So the kallsyms_lookup function and all related functions in the kernel
> do not work properly. For example, the stack trace in oops:
>
> Call Trace:
> [aa095e58] [809feab8] kobj_ns_ops_tbl+0x7ff09ac8/0x7ff1c1c4 (unreliable)
> [aa095e98] [80002b64] kobj_ns_ops_tbl+0x7f50db74/0x80000010
> [aa095ef8] [809c3d24] kobj_ns_ops_tbl+0x7feced34/0x7ff1c1c4
> [aa095f28] [80002ed0] kobj_ns_ops_tbl+0x7f50dee0/0x80000010
> [aa095f38] [8000f238] kobj_ns_ops_tbl+0x7f51a248/0x80000010
>
> The right stack trace:
>
> Call Trace:
> [aa095e58] [809feab8] module_vdu_video_init+0x2fc/0x3bc (unreliable)
> [aa095e98] [80002b64] do_one_initcall+0x40/0x1f0
> [aa095ef8] [809c3d24] kernel_init_freeable+0x164/0x1d8
> [aa095f28] [80002ed0] kernel_init+0x14/0x124
> [aa095f38] [8000f238] ret_from_kernel_thread+0x14/0x1c
>
> Signed-off-by: Mikhail Petrov <Mikhail.Petrov@xxxxxxx>
Applied with the following info:
[masahiroy@xxxxxxxxxx
This issue happens on binutils <= 2.22
The following commit fixed it:
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=d2667025dd30611514810c28bee9709e4623012a
The symbol type is 'T' on binutils >= 2.23
The current minimal supported binutils version is 2.21
]
Thanks.
> ---
>
> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> index 0133dfaaf352..3e8dea6e0a95 100644
> --- a/scripts/kallsyms.c
> +++ b/scripts/kallsyms.c
> @@ -195,13 +195,13 @@ static struct sym_entry *read_symbol(FILE *in)
> return NULL;
> }
>
> - if (is_ignored_symbol(name, type))
> - return NULL;
> -
> - /* Ignore most absolute/undefined (?) symbols. */
> if (strcmp(name, "_text") == 0)
> _text = addr;
>
> + /* Ignore most absolute/undefined (?) symbols. */
> + if (is_ignored_symbol(name, type))
> + return NULL;
> +
> check_symbol_range(name, addr, text_ranges, ARRAY_SIZE(text_ranges));
> check_symbol_range(name, addr, &percpu_range, 1);
>
--
Best Regards
Masahiro Yamada
