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Re: interesting option of stap
f-turgis wrote:
> [...] Hopefully I already digged some time ago in linker cmd file
> syntax and init call stuff so I am not 100% lost ;-). Here are my
> findings: [...]
Good job.
> - /sys/kernel/notes does not exist on these kernels. I found in all
> my kern els in .zImage.cmd "arm-linux-gnueabi-objcopy ... -R .note
> -R .note.gnu.build-id ... arch/arm/boot/compressed/vmlinux
> arch/arm/boot/zImage", -R being "Remove section xxx from the
> output". That could be why I don't see "notes" in the kernel.
Yes. Considering how small the .notes* are, it'd be reassuring to
have them be present in the linked image for runtime verification.
> Well, digging further, I simply read again the code and I found:
> /* Don't save build-id if it is located before _stext.
> * This probably means that build-id will not be loaded at all and
> * happens for example with ARM kernel.
> *
> * See also:
> * http://sources.redhat.com/ml/systemtap/2009-q4/msg00574.html
> */
> if (build_id_len > 0 && (build_id_vaddr > base + extra_offset)) {
> [...] commit 66f65c4fb0ddcdf8a85a29662a23a546cfd5dffe [put the test in]
> [...] commit 155bb07a5bfdd16b112870f7064f012970b7fbd9 [took the test out]
OK. So as a .note-less kernel compatibility measure, a
check-disabling kludge should be put back in, for kernels with a
suspicious build_id_vaddr.
- FChE