FROMLIST: BACKPORT: kbuild: fix dynamic ftrace with clang LTO

With CONFIG_LTO_CLANG enabled, LLVM IR won't be compiled into object
files until modpost_link. This change postpones calls to recordmcount
until after this step.

In order to exclude ftrace_process_locs from inspection, we add a new
code section .text..ftrace, which we tell recordmcount to ignore, and
a __norecordmcount attribute for moving functions to this section.

Bug: 62093296
Bug: 67506682
Change-Id: Iba2c053968206acf533fadab1eb34a743b5088ee
(am from https://patchwork.kernel.org/patch/10060327/)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

diff --git a/arch/Kconfig b/arch/Kconfig
index 5f96c8f..194d179 100644 (file)
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -503,7 +503,7 @@ config ARCH_SUPPORTS_LTO_CLANG
 config LTO_CLANG
        bool "Use clang Link Time Optimization (LTO) (EXPERIMENTAL)"
        depends on ARCH_SUPPORTS_LTO_CLANG
-       depends on !FTRACE_MCOUNT_RECORD
+       depends on !FTRACE_MCOUNT_RECORD || HAVE_C_RECORDMCOUNT
        select LTO
        select THIN_ARCHIVES
        select LD_DEAD_CODE_DATA_ELIMINATION

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index d1d7d5d..f2d0a7f 100644 (file)
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -460,6 +460,7 @@
 #define TEXT_TEXT                                                      \
                ALIGN_FUNCTION();                                       \
                *(.text.hot TEXT_MAIN .text.fixup .text.unlikely)       \
+               *(.text..ftrace)                                        \
                *(.ref.text)                                            \
        MEM_KEEP(init.text)                                             \
        MEM_KEEP(exit.text)                                             \

diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index de17999..fd29945 100644 (file)
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -15,3 +15,10 @@
  * with any version that can compile the kernel
  */
 #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
+
+#ifdef CONFIG_LTO_CLANG
+#ifdef CONFIG_FTRACE_MCOUNT_RECORD
+#define __norecordmcount \
+       __attribute__((__section__(".text..ftrace")))
+#endif
+#endif

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 5ce911d..40445d0 100644 (file)
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -451,6 +451,10 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
 #define __visible
 #endif
 
+#ifndef __norecordmcount
+#define __norecordmcount
+#endif
+
 /*
  * Assume alignment of return value.
  */

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 2884fe0..063dd22 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -4874,9 +4874,9 @@ static int ftrace_cmp_ips(const void *a, const void *b)
        return 0;
 }
 
-static int ftrace_process_locs(struct module *mod,
-                              unsigned long *start,
-                              unsigned long *end)
+static int __norecordmcount ftrace_process_locs(struct module *mod,
+                                               unsigned long *start,
+                                               unsigned long *end)
 {
        struct ftrace_page *start_pg;
        struct ftrace_page *pg;

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 4ce5e1a..5f113db 100644 (file)
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -244,6 +244,12 @@ ifdef BUILD_C_RECORDMCOUNT
 ifeq ("$(origin RECORDMCOUNT_WARN)", "command line")
   RECORDMCOUNT_FLAGS = -w
 endif
+
+ifdef CONFIG_LTO_CLANG
+# With LTO, we postpone running recordmcount until after the LTO link step, so
+# let's export the parameters for the link script.
+export RECORDMCOUNT_FLAGS
+else
 # Due to recursion, we must skip empty.o.
 # The empty.o file is created in the make process in order to determine
 #  the target endianness and word size. It is made before all other C
@@ -252,23 +258,29 @@ sub_cmd_record_mcount =                                   \
        if [ $(@) != "scripts/mod/empty.o" ]; then      \
                $(objtree)/scripts/recordmcount $(RECORDMCOUNT_FLAGS) "$(@)";   \
        fi;
+endif
+
 recordmcount_source := $(srctree)/scripts/recordmcount.c \
                    $(srctree)/scripts/recordmcount.h
-else
+else # !BUILD_C_RECORDMCOUNT
 sub_cmd_record_mcount = set -e ; perl $(srctree)/scripts/recordmcount.pl "$(ARCH)" \
        "$(if $(CONFIG_CPU_BIG_ENDIAN),big,little)" \
        "$(if $(CONFIG_64BIT),64,32)" \
        "$(OBJDUMP)" "$(OBJCOPY)" "$(CC) $(KBUILD_CFLAGS)" \
        "$(LD)" "$(NM)" "$(RM)" "$(MV)" \
        "$(if $(part-of-module),1,0)" "$(@)";
+
 recordmcount_source := $(srctree)/scripts/recordmcount.pl
-endif
+endif # BUILD_C_RECORDMCOUNT
+
+ifndef CONFIG_LTO_CLANG
 cmd_record_mcount =                                            \
        if [ "$(findstring $(CC_FLAGS_FTRACE),$(_c_flags))" =   \
             "$(CC_FLAGS_FTRACE)" ]; then                       \
                $(sub_cmd_record_mcount)                        \
        fi;
 endif
+endif # CONFIG_FTRACE_MCOUNT_RECORD
 
 ifdef CONFIG_STACK_VALIDATION
 ifneq ($(SKIP_STACK_VALIDATION),1)

diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index d26169b..b7c50cb 100644 (file)
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -143,6 +143,10 @@ ifdef CONFIG_LTO_CLANG
                        echo -T $(@:.ko=.o.symversions))                \
                 -o $@ --whole-archive                                  \
                 $(filter-out FORCE,$(^:$(modpost-ext).o=.o))
+
+  ifdef CONFIG_FTRACE_MCOUNT_RECORD
+      cmd_ld_ko_o += ; $(objtree)/scripts/recordmcount $(RECORDMCOUNT_FLAGS) $@
+  endif
 else
       cmd_ld_ko_o =                                                     \
        $(LD) -r $(LDFLAGS)                                             \

diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index d16dc7c..8b4329c 100755 (executable)
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -113,6 +113,19 @@ modpost_link()
        ${LD} ${LDFLAGS} -r -o ${1} $(modversions) ${objects}
 }
 
+# If CONFIG_LTO_CLANG is selected, we postpone running recordmcount until
+# we have compiled LLVM IR to an object file.
+recordmcount()
+{
+       if [ -z "${CONFIG_LTO_CLANG}" ]; then
+               return
+       fi
+
+       if [ -n "${CONFIG_FTRACE_MCOUNT_RECORD}" ]; then
+               scripts/recordmcount ${RECORDMCOUNT_FLAGS} $*
+       fi
+}
+
 # Link of vmlinux
 # ${1} - optional extra .o files
 # ${2} - output file
@@ -282,6 +295,9 @@ if [ -n "${CONFIG_LTO_CLANG}" ]; then
        # vmlinux_link
        KBUILD_VMLINUX_INIT=
        KBUILD_VMLINUX_MAIN=vmlinux.o
+
+       # Call recordmcount if needed
+       recordmcount vmlinux.o
 fi
 
 kallsymso=""

diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
index 5423a58..e0c5082 100644 (file)
--- a/scripts/recordmcount.c
+++ b/scripts/recordmcount.c
@@ -366,7 +366,8 @@ is_mcounted_section_name(char const *const txtname)
                strcmp(".softirqentry.text", txtname) == 0 ||
                strcmp(".kprobes.text", txtname) == 0 ||
                strcmp(".cpuidle.text", txtname) == 0 ||
-               strcmp(".text.unlikely", txtname) == 0;
+               (strncmp(".text.",       txtname, 6) == 0 &&
+                strcmp(".text..ftrace", txtname) != 0);
 }
 
 /* 32 bit and 64 bit are very similar */