objtool: Add --mnop as an option to --mcount

Some architectures (powerpc) may not support ftrace locations being nop'ed
out at build time. Introduce CONFIG_HAVE_OBJTOOL_NOP_MCOUNT for objtool, as
a means for architectures to enable nop'ing of ftrace locations. Add --mnop
as an option to objtool --mcount, to indicate support for the same.

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

Tested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221114175754.1131267-12-sv@linux.ibm.com

diff --git a/Makefile b/Makefile
index d148a55..53c2b71 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -933,7 +933,9 @@ ifdef CONFIG_FTRACE_MCOUNT_USE_CC
   endif
 endif
 ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
-  CC_FLAGS_USING       += -DCC_USING_NOP_MCOUNT
+  ifdef CONFIG_HAVE_OBJTOOL_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 67745ce..4be7c06 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -195,6 +195,7 @@ config X86
        select HAVE_CONTEXT_TRACKING_USER_OFFSTACK      if HAVE_CONTEXT_TRACKING_USER
        select HAVE_C_RECORDMCOUNT
        select HAVE_OBJTOOL_MCOUNT              if HAVE_OBJTOOL
+       select HAVE_OBJTOOL_NOP_MCOUNT          if HAVE_OBJTOOL_MCOUNT
        select HAVE_BUILDTIME_MCOUNT_SORT
        select HAVE_DEBUG_KMEMLEAK
        select HAVE_DMA_CONTIGUOUS

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index e9e95c7..2b78232 100644 (file)
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -82,6 +82,13 @@ config HAVE_OBJTOOL_MCOUNT
        help
          Arch supports objtool --mcount
 
+config HAVE_OBJTOOL_NOP_MCOUNT
+       bool
+       help
+         Arch supports the objtool options --mcount with --mnop.
+         An architecture can select this if it wants to enable nop'ing
+         of ftrace locations.
+
 config HAVE_C_RECORDMCOUNT
        bool
        help

diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 3aa384c..658f541 100644 (file)
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -256,6 +256,9 @@ objtool-args-$(CONFIG_HAVE_JUMP_LABEL_HACK)         += --hacks=jump_label
 objtool-args-$(CONFIG_HAVE_NOINSTR_HACK)               += --hacks=noinstr
 objtool-args-$(CONFIG_X86_KERNEL_IBT)                  += --ibt
 objtool-args-$(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL)       += --mcount
+ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
+objtool-args-$(CONFIG_HAVE_OBJTOOL_NOP_MCOUNT)         += --mnop
+endif
 objtool-args-$(CONFIG_UNWINDER_ORC)                    += --orc
 objtool-args-$(CONFIG_RETPOLINE)                       += --retpoline
 objtool-args-$(CONFIG_RETHUNK)                         += --rethunk

diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 24fbe80..9bd347d 100644 (file)
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -82,6 +82,7 @@ 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"),
@@ -150,6 +151,16 @@ 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)
@@ -198,6 +209,9 @@ 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 b64518c..71cf4b4 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1256,17 +1256,18 @@ 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 42a52f1..0785707 100644 (file)
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -31,6 +31,7 @@ struct opts {
        bool backup;
        bool dryrun;
        bool link;
+       bool mnop;
        bool module;
        bool no_unreachable;
        bool sec_address;