[RFC PATCH v3 04/12] objtool: Add --mnop as an option to --mcount

[Sathvika Vasireddy]

Architectures can select HAVE_NOP_MCOUNT if they choose
to nop out mcount call sites. If that config option is
selected, then --mnop is passed as an option to objtool,
along with --mcount.

Also, make sure that --mnop can be passed as an option
to objtool only when --mcount is passed.

Signed-off-by: Sathvika Vasireddy <s...@linux.ibm.com>
---
 Makefile                                |  4 +++-
 arch/x86/Kconfig                        |  1 +
 scripts/Makefile.build                  |  1 +
 tools/objtool/builtin-check.c           | 14 ++++++++++++++
 tools/objtool/check.c                   | 19 ++++++++++---------
 tools/objtool/include/objtool/builtin.h |  1 +
 6 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/Makefile b/Makefile
index 250707647359..acaf88e3c694 100644
--- a/Makefile
+++ b/Makefile
@@ -851,7 +851,9 @@ ifdef CONFIG_FTRACE_MCOUNT_USE_CC
   endif
 endif
 ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
-  CC_FLAGS_USING       += -DCC_USING_NOP_MCOUNT
+  ifdef CONFIG_HAVE_NOP_MCOUNT
+    CC_FLAGS_USING     += -DCC_USING_NOP_MCOUNT
+  endif
 endif
 ifdef CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT
   ifdef CONFIG_HAVE_C_RECORDMCOUNT
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 1847d6e974a1..4a41bfb644f0 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -189,6 +189,7 @@ config X86
        select HAVE_CONTEXT_TRACKING_OFFSTACK   if HAVE_CONTEXT_TRACKING
        select HAVE_C_RECORDMCOUNT
        select HAVE_OBJTOOL_MCOUNT              if HAVE_OBJTOOL
+       select HAVE_NOP_MCOUNT                  if HAVE_OBJTOOL_MCOUNT
        select HAVE_BUILDTIME_MCOUNT_SORT
        select HAVE_DEBUG_KMEMLEAK
        select HAVE_DMA_CONTIGUOUS
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index ac8167227bc0..2e0c3f9c1459 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -231,6 +231,7 @@ objtool_args =                                              
                \
        $(if $(CONFIG_HAVE_NOINSTR_HACK), --hacks=noinstr)              \
        $(if $(CONFIG_X86_KERNEL_IBT), --ibt)                           \
        $(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount)             \
+       $(if $(CONFIG_HAVE_NOP_MCOUNT), --mnop)                         \
        $(if $(CONFIG_UNWINDER_ORC), --orc)                             \
        $(if $(CONFIG_RETPOLINE), --retpoline)                          \
        $(if $(CONFIG_SLS), --sls)                                      \
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index f4c3a5091737..b05e2108c0c3 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -80,6 +80,7 @@ const struct option check_options[] = {
        OPT_BOOLEAN(0, "dry-run", &opts.dryrun, "don't write modifications"),
        OPT_BOOLEAN(0, "link", &opts.link, "object is a linked object"),
        OPT_BOOLEAN(0, "module", &opts.module, "object is part of a kernel 
module"),
+       OPT_BOOLEAN(0, "mnop", &opts.mnop, "nop out mcount call sites"),
        OPT_BOOLEAN(0, "no-unreachable", &opts.no_unreachable, "skip 
'unreachable instruction' warnings"),
        OPT_BOOLEAN(0, "sec-address", &opts.sec_address, "print section 
addresses in warnings"),
        OPT_BOOLEAN(0, "stats", &opts.stats, "print statistics"),
@@ -142,6 +143,16 @@ static bool opts_valid(void)
        return false;
 }
 
+static bool mnop_opts_valid(void)
+{
+       if (opts.mnop && !opts.mcount) {
+               ERROR("--mnop requires --mcount");
+               return false;
+       }
+
+       return true;
+}
+
 static bool link_opts_valid(struct objtool_file *file)
 {
        if (opts.link)
@@ -185,6 +196,9 @@ int objtool_run(int argc, const char **argv)
        if (!file)
                return 1;
 
+       if (!mnop_opts_valid())
+               return 1;
+
        if (!link_opts_valid(file))
                return 1;
 
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index fabc0ea88747..7f0dc504dd92 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1177,17 +1177,18 @@ static void annotate_call_site(struct objtool_file 
*file,
        if (opts.mcount && sym->fentry) {
                if (sibling)
                        WARN_FUNC("Tail call to __fentry__ !?!?", insn->sec, 
insn->offset);
+               if (opts.mnop) {
+                       if (reloc) {
+                               reloc->type = R_NONE;
+                               elf_write_reloc(file->elf, reloc);
+                       }
 
-               if (reloc) {
-                       reloc->type = R_NONE;
-                       elf_write_reloc(file->elf, reloc);
-               }
-
-               elf_write_insn(file->elf, insn->sec,
-                              insn->offset, insn->len,
-                              arch_nop_insn(insn->len));
+                       elf_write_insn(file->elf, insn->sec,
+                                      insn->offset, insn->len,
+                                      arch_nop_insn(insn->len));
 
-               insn->type = INSN_NOP;
+                       insn->type = INSN_NOP;
+               }
 
                list_add_tail(&insn->call_node, &file->mcount_loc_list);
                return;
diff --git a/tools/objtool/include/objtool/builtin.h 
b/tools/objtool/include/objtool/builtin.h
index 280ea18b7f2b..71ed3152a18e 100644
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -29,6 +29,7 @@ struct opts {
        bool backup;
        bool dryrun;
        bool link;
+       bool mnop;
        bool module;
        bool no_unreachable;
        bool sec_address;
-- 
2.25.1