[PATCH v4 11/16] objtool: Add --mnop as an option to --mcount

Sathvika Vasireddy
2022-10-02T10:46:03Z

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.

Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
---
Makefile | 4 +++-
arch/x86/Kconfig | 1 +
kernel/trace/Kconfig | 7 +++++++
scripts/Makefile.lib | 1 +
tools/objtool/builtin-check.c | 14 ++++++++++++++
tools/objtool/check.c | 19 ++++++++++---------
tools/objtool/include/objtool/builtin.h | 1 +
7 files changed, 37 insertions(+), 10 deletions(-)

diff --git a/Makefile b/Makefile
index a5e9d9388649..b2230ad14748 100644
--- a/Makefile
+++ b/Makefile
@@ -857,7 +857,9 @@ 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 f9920f1341c8..2a79a05c4402 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -189,6 +189,7 @@ 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 1052126bdca2..9c696cb24756 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -76,6 +76,13 @@ 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 3fb6a99e78c4..ce14e3b8577f 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -234,6 +234,7 @@ 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_OBJTOOL_NOP_MCOUNT), --mnop) \
$(if $(CONFIG_UNWINDER_ORC), --orc) \
$(if $(CONFIG_RETPOLINE), --retpoline) \
$(if $(CONFIG_RETHUNK), --rethunk) \
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 24fbe803a0d3..9bd347d3c244 100644
--- 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 738de23cb9e8..35827e6c6df9 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1233,17 +1233,18 @@ 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 42a52f1a0add..0785707c5a92 100644
--- 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;
--
2.31.1