tree e0a7d2db2f5a404013780461f72414788ee5f49d
parent 88b1a8547f4c00e55d54e081fc15e3980debf5c1
author Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> 1524121447 +0530
committer Michael Ellerman <mpe@ellerman.id.au> 1525350748 +1000

powerpc64/module: Tighten detection of mcount call sites with -mprofile-kernel

For R_PPC64_REL24 relocations, we suppress emitting instructions for TOC
load/restore in the relocation stub if the relocation is for _mcount()
call when using -mprofile-kernel ABI.

To detect this, we check if the preceding instructions are per the
standard set of instructions emitted by gcc: either the two instruction
sequence of 'mflr r0; std r0,16(r1)', or the more optimized variant of a
single 'mflr r0'. This is not sufficient since nothing prevents users
from hand coding sequences involving a 'mflr r0' followed by a 'bl'.

For removing the toc save instruction from the stub, we additionally
check if the symbol is "_mcount". Add the same check here as well.

Also rename is_early_mcount_callsite() to is_mprofile_mcount_callsite()
since that is what is being checked. The use of "early" is misleading
since there is nothing involving this function that qualifies as early.

Fixes: 153086644fd1f ("powerpc/ftrace: Add support for -mprofile-kernel ftrace ABI")
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>