amd64 kernel modules: mapping sections to addresses

Andriy Gapon avg at
Mon Jun 21 14:39:12 UTC 2010

I've noticed that on amd64 addresses (sh_addr) of all sections in a kernel module
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 requirements.

On the other hand, kgdb calculates section address as module base address plus
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 section
described in a header.

DTrace situation is even worse, because don't even take into account module base
address, not speaking of section relative addresses.

Perhaps we should put some sh_addr values into amd64 kernel modules that would
match calculations done in link_elf_load_file.
Or should we replicate logic from link_elf_load_file in all places that need to
map loaded module's sections to load addresses?

What do you think?

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?

Andriy Gapon

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