dtrace: move _sdt_probes array into a separately-compiled file

This means we no longer need to worry about whether Linux kernel headers
include prototypes that we are declaring probes for, and can just
unconditionally declare them.  Having an exclusion list turned out to
be untenable, because the set of headers transitively included from
<linux/module.h> depends on kernel configuration as well as
architecture: but *.sdtinfo.c only depends on <linux/sdt.h>, which is
entirely under our control and we know includes no prototypes of
anything that we might ever want to probe.  We generate a separate
.h file that only includes _sdt_probec and an extern definition
of _sdt_probes, and include that from the .mod.c: the full definition of
_sdt_probec is now separately compiled

One downside is that we lie to make slightly now, telling it that
*.mod.c depends on *.sdtinfo.c, when actually it depends on *.sdtinfo.h:
but the two are generated by the same script at the same time so this
isn't going to cause a problem.

Signed-off-by: Nick Alcock <nick.alcock@oracle.com>

.gitignore

@@ -160,4 +160,5 @@ x509.genkey
 # Generated DTrace SDT files
 #
 *.sdtinfo.c
+*.sdtinfo.h
 *.sdtstub.S

Makefile

@@ -1861,7 +1861,7 @@ clean: $(clean-dirs)
 		-o -name '*.dtb' -o -name '*.dtb.S' -o -name '*.dt.yaml' \
 		-o -name '*.dwo' -o -name '*.lst' \
 		-o -name '*.su' -o -name '*.mod' \
-		-o -name '*.sdtinfo.c' -o -name '*.sdtstub.S' \
+		-o -name '*.sdtinfo.c' -o -name '*.sdtinfo.h' -o -name '*.sdtstub.S' \
 		-o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \
 		-o -name '*.lex.c' -o -name '*.tab.[ch]' \
 		-o -name '*.asn1.[ch]' \

scripts/Makefile.modfinal

@@ -42,7 +42,7 @@ ifdef CONFIG_DTRACE
 sdtgen = $(srctree)/scripts/dtrace_sdt.sh
 
 quiet_cmd_sdtinfo = SDTINF  $@
-      cmd_sdtinfo = $(sdtgen) sdtinfo $@ $< kmod
+      cmd_sdtinfo = $(sdtgen) sdtinfo $@ $< kmod $(@:.c=.h)
 
 quiet_cmd_sdtstub = SDTSTB  $@
       cmd_sdtstub = $(sdtgen) sdtstub $@ $<
@@ -56,6 +56,9 @@ $(modules:.ko=.sdtinfo.c): %.sdtinfo.c: %.o %.mod.c
 $(modules:.ko=.sdtstub.S) : %.sdtstub.S: %.o %.sdtinfo.c
 	$(call cmd,sdtstub)
 
+%.sdtinfo.o : %.sdtinfo.c
+	$(call if_changed_dep,cc_o_c)
+
 %.mod.o: %.mod.c %.sdtinfo.c FORCE
 	$(call if_changed_dep,cc_o_c)
 
@@ -210,7 +213,7 @@ quiet_cmd_ld_ko_o = LD [M]  $@
         $(OBJCOPY) $(module-ctf-flags) $@.tmp $@ && rm -f $@.tmp ;	\
 	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
 
-$(modules): %.ko: %.o %.mod.o $(KBUILD_LDS_MODULE) $(module-sdt-modular-prereq) $(module-ctfs-modular-prereq) FORCE
+$(modules): %.ko: %.o %.mod.o %.sdtinfo.o $(KBUILD_LDS_MODULE) $(module-sdt-modular-prereq) $(module-ctfs-modular-prereq) FORCE
 	$(call cmd_touch_ctf)
 	+$(call if_changed,ld_ko_o)
 

scripts/dtrace_sdt.sh

@@ -8,9 +8,9 @@ LANG=C
 #	dtrace_sdt.sh sdtstub <S-file> <o-file>+
 #		This is used to generate DTrace SDT probe stubs based on one
 #		or more object file(s).  The stubs are written to <S-file>.
-#	dtrace_sdt.sh sdtinfo <c-file> <o-file> kmod
+#	dtrace_sdt.sh sdtinfo <c-file> <o-file> kmod <h-file>
 #		This is used to generate DTrace SDT probe definitions for a
-#		kmod .o file.  The output is written to <c-file>.
+#		kmod .o file.  The output is written to <c-file> and <h-file>.
 #	dtrace_sdt.sh sdtinfo <S-file> <l-file>
 #		This is used to generate DTrace SDT probe definitions for a
 #		linked kernel image file <l-file>.  The output is written to
@@ -71,6 +71,8 @@ if [ "$opr" != "sdtinfo" ]; then
 fi
 
 if [ "$tok" = "kmod" ]; then
+    hfile="$3"
+
     # Pre-process the object file to handle any local functions that contain
     # SDT probes.
     scripts/kmodsdt ${ofn}
@@ -143,7 +145,7 @@ if [ "$tok" = "kmod" ]; then
 		 print $4 " " $1 " F " $6;
 	 }' | \
     sort -k1,2 | \
-    gawk -v arch=${ARCH} \
+    gawk -v arch=${ARCH} -v hfile=${hfile} \
 	'function subl(v0, v1, v0h, v0l, v1h, v1l, d, tmp) {
              tmp = $0;
              if (length(v0) > 8) {
@@ -185,7 +187,6 @@ if [ "$tok" = "kmod" ]; then
 
 	 BEGIN {
 	     print "#include <linux/sdt.h>";
-	     print "#include <linux/fs.h>";
 
 	     probec = 0;
 	 }
@@ -240,18 +241,15 @@ if [ "$tok" = "kmod" ]; then
 	 }
 
 	 END {
-	     if (probec > 0) {
-		 for (alias in protom)
-		     if (alias != "locks_start_grace" && alias != "locks_end_grace")
-			 printf "extern void %s(void);\n", alias;
-		 print "\nstatic struct sdt_probedesc\t_sdt_probes[] = {";
-		 for (i = 0; i < probec; i++)
-		     print probev[i];
-		 print "};\n";
-	     } else
-		print "#define _sdt_probes\tNULL";
-
-	     print "#define _sdt_probec\t" probec;
+	     for (alias in protom)
+		 printf "extern void %s(void);\n", alias;
+	     print "\nstruct sdt_probedesc\t_sdt_probes[] = {";
+	     for (i = 0; i < probec; i++)
+		 print probev[i];
+	     print "};\n";
+
+	     print "#define _sdt_probec\t" probec > hfile;
+	     print "extern struct sdt_probedesc _sdt_probes[];" >> hfile;
 
 	     exit(errc == 0 ? 0 : 1);
 	 }' > $tfn

scripts/mod/modpost.c

@@ -2258,7 +2258,7 @@ static void add_header(struct buffer *b, struct module *mod)
 	buf_printf(b, "#include <linux/compiler.h>\n");
 	buf_printf(b, "\n");
 	buf_printf(b, "#ifdef CONFIG_DTRACE\n");
-	buf_printf(b, "# include \"%s.sdtinfo.c\"\n", modname);
+	buf_printf(b, "# include \"%s.sdtinfo.h\"\n", modname);
 	buf_printf(b, "#endif\n");
 	buf_printf(b, "\n");
 	buf_printf(b, "BUILD_SALT;\n");