On 2023/07/24 16:33, lijiang wrote:
> On Mon, Jul 24, 2023 at 3:07 PM HAGIO KAZUHITO(萩尾 一仁) <k-hagio-ab@nec.com>
> wrote:
>
>> On 2023/07/24 15:51, lijiang wrote:
>>> How about reading out the linux_banner string to a buffer with readmem()?
>>
>> No, this is a version check for the namelist (vmlinux).
>>
>>
> Ah, you are right, Kazu.
>
>>> If the vmlinux does not have only the ".rodata" symbol, is it possible
>>>> to use "__start_rodata" symbol or something?  i.e. is there no symbol
>>>> that has the same address as .rodata section?
>>>>
>>>>
>>> I tried the "__start_rodata" symbol, but it does not work.
>>
>> How did you try?  There is no "__start_rodata" symbol?
>>
>> I mean something like this:
>>
>> --- a/kernel.c
>> +++ b/kernel.c
>> @@ -11893,8 +11893,13 @@ int get_linux_banner_from_vmlinux(char *buf,
>> size_t size)
>>    {
>>           struct bfd_section *sect;
>>           long offset;
>> +       ulong start_rodata;
>>
>> -       if (!kernel_symbol_exists(".rodata"))
>> +       if (kernel_symbol_exists(".rodata"))
>> +               start_rodata = symbol_value(".rodata");
>> +       else if (kernel_symbol_exists("__start_rodata"))
>> +               start_rodata = symbol_value("__start_rodata");
>> +       else
>>                   return FALSE;
>>
>>           sect = bfd_get_section_by_name(st->bfd, ".rodata");
>>
>
> The ".rodata" is a section, I mistakenly replaced the ".rodata" with the
> symbol "__start_rodata" in a debug patch, so it does not work. :-)
>
> diff --git a/kernel.c b/kernel.c
> index 546eed9..3c50fa4 100644
> --- a/kernel.c
> +++ b/kernel.c
> @@ -11894,7 +11894,7 @@ int get_linux_banner_from_vmlinux(char *buf, size_t
> size)
>          struct bfd_section *sect;
>          long offset;
>
> -       if (!kernel_symbol_exists(".rodata"))
> +       if (!kernel_symbol_exists("__start_rodata"))
>                  return FALSE;
>
>          sect = bfd_get_section_by_name(st->bfd, ".rodata");
> @@ -11907,7 +11907,7 @@ int get_linux_banner_from_vmlinux(char *buf, size_t
> size)
>           * value in vmlinux file, but relative offset to linux_banner
>           * object in .rodata section is idential.
>           */
> -       offset = symbol_value("linux_banner") - symbol_value(".rodata");
> +       offset = symbol_value("linux_banner") -
> symbol_value("__start_rodata");
>
>          if (!bfd_get_section_contents(st->bfd,
>                                        sect,
> @@ -11916,5 +11916,6 @@ int get_linux_banner_from_vmlinux(char *buf, size_t
> size)
>                                        size))
>                  return FALSE;
>
> +       error(INFO, "%s\n", buf);
>          return TRUE;
>
> For now, the get_linux_banner_from_vmlinux() works again with the debug
> patch.

Good, thanks for the test.  I will send a patch for this.