amd64 kernel modules: mapping sections to addresses

John Baldwin jhb at
Mon Jun 21 15:43:52 UTC 2010

On Monday 21 June 2010 10:39:08 am Andriy Gapon wrote:
> I've noticed that on amd64 addresses (sh_addr) of all sections in a kernel 
> are zeros.
> This is unlike kernel itself and i386 modules.
> Kernel linker maps SHT_PROGBITS and SHT_NOBITS sections sequentially 
starting at a
> certain base address and taking into account their sizes and alignment 
> On the other hand, kgdb calculates section address as module base address 
> sh_addr of the section.  Which puts all sections, e.g. .text, .data, .bss, 
at the
> same address.  This is correct only for .text which is normally the first 
> described in a header.
> DTrace situation is even worse, because don't even take into account module 
> address, not speaking of section relative addresses.
> Perhaps we should put some sh_addr values into amd64 kernel modules that 
> match calculations done in link_elf_load_file.
> Or should we replicate logic from link_elf_load_file in all places that need 
> map loaded module's sections to load addresses?
> What do you think?
> Thanks!
> P.S.
> As I understand CTF data includes a symbol table.
> What kind of symbol addresses is used there?  Are they relative within a
> corresponding section?  Or something else?

np@ has a patch to gdb to fix this for kgdb.  I haven't committed it as it 
patched gdb internals and wasn't in a kgdb-specific place, but I'm not sure of 
a better way to fix kgdb.

John Baldwin

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