[PATCH v4 00/16] objtool: Enable and implement --mcount option on powerpc

[Naveen N. Rao]

Sathvika Vasireddy wrote:
> This patchset enables and implements objtool --mcount
> option on powerpc. This applies atop powerpc/merge branch.
> 
> Changelog:
> 
> ----
> v4:
> 
> * Patch 11/16 - Introduce a new config option
> 		CONFIG_HAVE_OBJTOOL_NOP_MCOUNT as a means for
> 		architectures to enable nop'ing ftrace locations.
> 
> 	      - Remove Acked-by tag from Peter Zijlstra (Intel),
> 		and Reviewed-by tag from Christophe Leroy. 
> 		[This is done because I reworked the patch to add
> 		a new config option to objtool. Please let me know
> 		if you want me to retain the tags. Thanks!]
> 
> * Patch 16/16 - Rework the patch to handle only 'bl' instruction
> 		decoding. 

With changes to the two patches in this series that I have described, 
and with my patch to have ftrace ignore weak symbols (*) applied, I 
built a ppc64le config.

(*) http://lkml.kernel.org/r/20220809105425.424045-1-naveen.n.rao@linux.vnet.ibm.com

I then used the below diff to disable objtool and to build with 
recordmcount:

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 7e28a8fd4c24fa..81c9f895d69012 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -238,8 +238,6 @@ config PPC
        select HAVE_MOD_ARCH_SPECIFIC
        select HAVE_NMI                         if PERF_EVENTS || (PPC64 && PPC_BOOK3S)
        select HAVE_OPTPROBES
-       select HAVE_OBJTOOL                     if PPC32 || MPROFILE_KERNEL
-       select HAVE_OBJTOOL_MCOUNT              if HAVE_OBJTOOL
        select HAVE_PERF_EVENTS
        select HAVE_PERF_EVENTS_NMI             if PPC64
        select HAVE_PERF_REGS

Comparing available_filter_functions across the two builds showed the 
below differences:
  $ diff ftrace_funcs_recordmcount_20221010.sort.out ftrace_funcs_objtool_20221010.sort.out 
  6799d6798
  < __dev_alloc_name
  6800a6800
  > dev_alloc_name_ns
  11680d11679
  < find_zone.isra.0
  22396a22396
  > ns_capable_common.part.0

All the above changes are down to compiler optimizations and shuffling 
due to CONFIG_OBJTOOL being enabled and changing annotate_unreachable().

As such, for this series:
Reviewed-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
Tested-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>


Josh,
Are you ok if this series is taken in through the powerpc tree?


- Naveen