On 2023/07/24 15:51, lijiang wrote:
>>> I think you are fixing the fallback routine and that's good, but it's
>>> better to fix get_linux_banner_from_vmlinux() first if possible. It's
>>
>
> Thank you for the comments, Kazu.
>
> They are different issues. The fallback routine(strings) also needs to be
> fixed, and the get_linux_banner_from_vmlinux() failure is another issue.
Yes, will merge this later.
>
>> much faster. Isn't it possible?
>>>
>
>
> As I mentioned in patch log, the symbol ".rodata" was not found in some
> vmlinux, and so far I haven't got any equivalent symbols to achieve the
> purpose.
>
> crash> sym .rodata
> symbol not found: .rodata
> possible alternatives:
> (none found)
> crash>
>
> But the following change works well for this case:
>
> diff --git a/kernel.c b/kernel.c
> index 546eed9..a4ce5bf 100644
> --- a/kernel.c
> +++ b/kernel.c
> @@ -11891,6 +11891,7 @@ check_vmcoreinfo(void)
> static
> int get_linux_banner_from_vmlinux(char *buf, size_t size)
> {
> +#if 0
> struct bfd_section *sect;
> long offset;
>
> @@ -11917,4 +11918,10 @@ int get_linux_banner_from_vmlinux(char *buf,
> size_t size)
> return FALSE;
>
> return TRUE;
> +#else
> + if (!readmem(symbol_value("linux_banner"), KVADDR, buf, size,
> "linux_banner", RETURN_ON_ERROR))
> + return FALSE;
> +
> + return TRUE;
> +#endif
> }
>
> How about reading out the linux_banner string to a buffer with readmem()?
No, this is a version check for the namelist (vmlinux).
>
>
>>> What do you see in "sections:" in "help -s"? And probably you can
>>> determine the section where linux_banner is located, with the address of
>>> linux_banner and KASLR offset.
>>>
>>> crash> help -s
>>> ...
>>> sections:
>>> .text vma: ffffffff81000000 size: 14686984
>>> .rodata vma: ffffffff82000000 size: 5366231
>>> .pci_fixup vma: ffffffff8251e1e0 size: 14112
>>> ...
>>> crash> sym linux_banner
>>> ffffffffb5200a40 (D) linux_banner
>>> crash> help -D | grep KERNELOFFSET
>>> KERNELOFFSET=33200000
>>>
>>> crash> eval ffffffffb5200a40 - 0x33200000
>>> hexadecimal: ffffffff82000a40 --> linux_banner is in ".rodata"
>>
>> 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");
@@ -11907,7 +11912,7 @@ 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") - start_rodata;
if (!bfd_get_section_contents(st->bfd,
sect,
Thanks,
Kazu
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