Re: [PATCH] Fix warning about kernel version inconsistency during crash startup

[lijiang <lijiang@xxxxxxxxxx>]

On Mon, Jul 24, 2023 at 3:07 PM HAGIO KAZUHITO(萩尾　一仁) <k-hagio-ab@xxxxxxx> 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.

Thanks.

Lianbo

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