Roland McGrath wrote:
> The case of non-EXEC is in .rodata of vmlinux. A single die that
comes
> from arch/x86/kernel/trampoline_32.S has this property. So I shift my
> understanding of low_pc and high_pc from "we can expect PC to have this
> address" to "it's a place in address space".
I looked at this case. It's an oddball, but valid. That code is in
.rodata because it's not actually run there, but copied to different
addresses at runtime. It's a kosher CU from as -g producing line info.
These "PC" addresses will never map usefully from where a PC really is at
runtime, but statically it is a kosher and useful mapping from where the
code appears at its symbol. i.e., eu-addr2line -e vmlinux trampoline_data+0
This is sufficiently unusual that it might still warrant a warning. But if
it looks otherwise kosher, e.g. is SHF_ALLOC and not SHF_WRITE, it could
mention "might be nonexecuted code in rodata" or something.
Hmm, but looking at the source, it is sometimes in a writable section here
(.cpuinit.data, depends on kernel config).
Other than this one case, it seems about as likely that it would be due to
a build error as to an authentic oddball like this. But, there is nothing
technically invalid (or even necessarily "suspicious") about it from a pure
DWARF perspective.
Thanks for the analysis, will implement this tomorrow.
> Another case is basically any GRUB module. These have
relocations of
> low_pc and high_pc formed against .moddeps, which is non-ALLOC section
> (which, if I understand things correctly, means it doesn't end up in
> address space at all).
I'm not sure I found the right things to look at, since I did not find any
.moddeps sections where I looked. Can you point me to a particular example
(rpm id + file name)?
One of the modules was this one:
./i586/gr/ub/grub2-debuginfo-1.98-0.5.20080827svn.fc11.i586/usr/lib/debug/usr/lib/grub2/i386-pc/sleep.mod.debug.bz2
And the relevant message from my locally hacked version:
warning: .rel.debug_info: offset 0x50b: associated section #13 isn't
SHF_ALLOC.
It tells something different on the branch, I didn't commit this change
yet, but it should give some sort of diagnostic for that relocation.
Thanks,
PM