Re: [PATCH] markers: modpost

David Smith
2007-11-08T19:32:25Z

Mathieu Desnoyers wrote:
> * Roland McGrath (roland@redhat.com) wrote:
>>> If we want to do it safely, I think we should iterate from
>>> __start___markers to __stop___markers symbols of vmlinux and get the
>>> pointers to the name/format string pairs.
>>>
>>> The same can then be done with modules using the __markers section.
>>>
>>> Or maybe is there some reason not to do that ?
>> It's just rather a pain in the ass, a whole lot more fiddly work.
>> cf "somewhat crude" and "foreseeable future" in my patch's log entry.
>> Knock yourself out if you're looking for more tedious hacking to do in
>> modpost.c, but I say fix it when it breaks.
>>
>
> Hmmmm, I have rarely seen code go into mainline without addressing valid
> technical criticism first. Please fix.
>
> I'll look into it if I find the time.
>
> Mathieu

Mathieu,

Here's an updated patch, written by Roland (that I tested for him), that
looks for all marker symbols in the __markers_strings section. It doesn't
get the pointers from the __markers section because that is very difficult
to do in modpost (having to handle the architecture-dependent relocations
applied to those pointers).

See what you think.

---
This adds some new magic in the MODPOST phase for CONFIG_MARKERS.
Analogous to the Module.symvers file, the build will now write a
Module.markers file when CONFIG_MARKERS=y is set. This file lists
the name, defining module, and format string of each marker,
separated by \t characters. This simple text file can be used by
offline build procedures for instrumentation code, analogous to
how System.map and Module.symvers can be useful to have for
kernels other than the one you are running right now.

The method of extracting the strings is somewhat crude, but is pretty
simple and should work fine in practice for the foreseeable future.

Signed-off-by: Roland McGrath <roland@redhat.com>
---
scripts/Makefile.modpost | 11 +++
scripts/mod/modpost.c | 184 +++++++++++++++++++++++++++++++++++++++++++++-
scripts/mod/modpost.h | 3 +
3 files changed, 197 insertions(+), 1 deletions(-)

diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index d988f5d..6321870 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -13,6 +13,7 @@
# 2) modpost is then used to
# 3) create one <module>.mod.c file pr. module
# 4) create one Module.symvers file with CRC for all exported symbols
+# 4a) [CONFIG_MARKERS] create one Module.markers file listing defined markers
# 5) compile all <module>.mod.c files
# 6) final link of the module to a <module.ko> file

@@ -45,6 +46,10 @@ include scripts/Makefile.lib

kernelsymfile := $(objtree)/Module.symvers
modulesymfile := $(firstword $(KBUILD_EXTMOD))/Module.symvers
+kernelmarkersfile := $(objtree)/Module.markers
+modulemarkersfile := $(firstword $(KBUILD_EXTMOD))/Module.markers
+
+markersfile = $(if $(KBUILD_EXTMOD),$(modulemarkersfile),$(kernelmarkersfile))

# Step 1), find all modules listed in $(MODVERDIR)/
__modules := $(sort $(shell grep -h '\.ko' /dev/null $(wildcard $(MODVERDIR)/*.mod)))
@@ -62,6 +67,8 @@ modpost = scripts/mod/modpost \
$(if $(KBUILD_EXTMOD),-i,-o) $(kernelsymfile) \
$(if $(KBUILD_EXTMOD),-I $(modulesymfile)) \
$(if $(KBUILD_EXTMOD),-o $(modulesymfile)) \
+ $(if $(CONFIG_MARKERS),-K $(kernelmarkersfile)) \
+ $(if $(CONFIG_MARKERS),-M $(markersfile)) \
$(if $(KBUILD_EXTMOD)$(KBUILD_MODPOST_WARN),-w)

quiet_cmd_modpost = MODPOST $(words $(filter-out vmlinux FORCE, $^)) modules
@@ -81,6 +88,10 @@ vmlinux.o: FORCE
$(symverfile): __modpost ;
$(modules:.ko=.mod.c): __modpost ;

+ifdef CONFIG_MARKERS
+$(markersfile): __modpost ;
+endif
+

# Step 5), compile all *.mod.c files

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 93ac52a..bbaf26d 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -11,6 +11,8 @@
* Usage: modpost vmlinux module1.o module2.o ...
*/

+#define _GNU_SOURCE
+#include <stdio.h>
#include <ctype.h>
#include "modpost.h"
#include "../../include/linux/license.h"
@@ -424,6 +426,8 @@ static int parse_elf(struct elf_info *info, const char *filename)
info->export_unused_gpl_sec = i;
else if (strcmp(secname, "__ksymtab_gpl_future") == 0)
info->export_gpl_future_sec = i;
+ else if (strcmp(secname, "__markers_strings") == 0)
+ info->markers_strings_sec = i;

if (sechdrs[i].sh_type != SHT_SYMTAB)
continue;
@@ -1249,6 +1253,83 @@ static int exit_section_ref_ok(const char *name)
return 0;
}

+static void get_markers(struct elf_info *info, struct module *mod)
+{
+ const Elf_Shdr *sh = &info->sechdrs[info->markers_strings_sec];
+ const char *strings = (const char *) info->hdr + sh->sh_offset;
+ const Elf_Sym *sym, *first_sym, *last_sym;
+ const char *name;
+ size_t n;
+
+ if (!info->markers_strings_sec)
+ return;
+
+ /*
+ * First count the strings. They come in pairs of name, format.
+ * We look for all the symbols defined in the __markers_strings
+ * section. They are named __mstrtab_name_* and __mstrtab_format_*
+ * in matching pairs. For these local names, the compiler puts
+ * a random .NNN suffix on, so the names don't correspond exactly.
+ */
+ first_sym = last_sym = NULL;
+ n = 0;
+ for (sym = info->symtab_start; sym < info->symtab_stop; sym++)
+ if (ELF_ST_TYPE(sym->st_info) == STT_OBJECT &&
+ sym->st_shndx == info->markers_strings_sec) {
+ if (first_sym == NULL)
+ first_sym = sym;
+ last_sym = sym;
+ ++n;
+ name = info->strtab + sym->st_name;
+ if (n % 2 == 0 ?
+ !strncmp(name, "__mstrtab_name_",
+ sizeof "__mstrtab_name_" - 1) :
+ !strncmp(name, "__mstrtab_format_",
+ sizeof "__mstrtab_format_" - 1)) {
+ warn("%s.ko has unexpected symbol \"%s\"\n",
+ mod->name, name);
+ first_sym = NULL;
+ }
+ }
+
+ if (n % 2 != 0 || first_sym == NULL) {
+ warn("%s.ko has bad __markers_strings, ignoring it\n",
+ mod->name);
+ return;
+ }
+
+ if (n == 0)
+ return;
+
+ /*
+ * Now collect each pair into a formatted line for the output.
+ * Lines look like:
+ * marker_name vmlinux marker %s format %d
+ * The format string after the second \t can use whitespace.
+ */
+ n /= 2;
+ mod->markers = NOFAIL(malloc(sizeof mod->markers[0] * n));
+ mod->nmarkers = n;
+
+ name = NULL;
+ n = 0;
+ for (sym = first_sym; sym <= last_sym; sym++)
+ if (ELF_ST_TYPE(sym->st_info) == STT_OBJECT &&
+ sym->st_shndx == info->markers_strings_sec) {
+ const char *str = strings + sym->st_value;
+ if (name == NULL)
+ name = str;
+ else {
+ char *line = NULL;
+ asprintf(&line, "%s\t%s\t%s\n",
+ name, mod->name, str);
+ NOFAIL(line);
+ mod->markers[n++] = line;
+ name = NULL;
+ }
+ }
+}
+
static void read_symbols(char *modname)
{
const char *symname;
@@ -1301,6 +1382,8 @@ static void read_symbols(char *modname)
get_src_version(modname, mod->srcversion,
sizeof(mod->srcversion)-1);

+ get_markers(&info, mod);
+
parse_elf_finish(&info);

/* Our trick to get versioning for struct_module - it's
@@ -1649,6 +1732,91 @@ static void write_dump(const char *fname)
write_if_changed(&buf, fname);
}

+static void add_marker(struct module *mod, const char *name, const char *fmt)
+{
+ char *line = NULL;
+ asprintf(&line, "%s\t%s\t%s\n", name, mod->name, fmt);
+ NOFAIL(line);
+
+ mod->markers = NOFAIL(realloc(mod->markers, ((mod->nmarkers + 1) *
+ sizeof mod->markers[0])));
+ mod->markers[mod->nmarkers++] = line;
+}
+
+static void read_markers(const char *fname)
+{
+ unsigned long size, pos = 0;
+ void *file = grab_file(fname, &size);
+ char *line;
+
+ if (!file)
+ /* No old markers, silently ignore */
+ return;
+
+ while ((line = get_next_line(&pos, file, size))) {
+ char *marker, *modname, *fmt;
+ struct module *mod;
+
+ marker = line;
+ if (!(modname = strchr(marker, '\t')))
+ goto fail;
+ *modname++ = '\0';
+ if (!(fmt = strchr(modname, '\t')))
+ goto fail;
+ *fmt++ = '\0';
+ if (*marker == '\0' || *modname == '\0')
+ goto fail;
+
+ if (!(mod = find_module(modname))) {
+ if (is_vmlinux(modname)) {
+ have_vmlinux = 1;
+ }
+ mod = new_module(NOFAIL(strdup(modname)));
+ mod->skip = 1;
+ }
+
+ add_marker(mod, marker, fmt);
+ }
+ return;
+fail:
+ fatal("parse error in markers list file\n");
+}
+
+static int compare_strings(const void *a, const void *b)
+{
+ return strcmp(*(const char **) a, *(const char **) b);
+}
+
+static void write_markers(const char *fname)
+{
+ struct buffer buf = { };
+ struct module *mod;
+ size_t i;
+
+ for (mod = modules; mod; mod = mod->next)
+ if ((!external_module || !mod->skip) && mod->markers != NULL) {
+ /*
+ * Sort the strings so we can skip duplicates when
+ * we write them out.
+ */
+ qsort(mod->markers, mod->nmarkers,
+ sizeof mod->markers[0], &compare_strings);
+ for (i = 0; i < mod->nmarkers; ++i) {
+ char *line = mod->markers[i];
+ buf_write(&buf, line, strlen(line));
+ while (i + 1 < mod->nmarkers &&
+ !strcmp(mod->markers[i],
+ mod->markers[i + 1]))
+ free(mod->markers[i++]);
+ free(mod->markers[i]);
+ }
+ free(mod->markers);
+ mod->markers = NULL;
+ }
+
+ write_if_changed(&buf, fname);
+}
+
int main(int argc, char **argv)
{
struct module *mod;
@@ -1656,10 +1824,12 @@ int main(int argc, char **argv)
char fname[SZ];
char *kernel_read = NULL, *module_read = NULL;
char *dump_write = NULL;
+ char *markers_read = NULL;
+ char *markers_write = NULL;
int opt;
int err;

- while ((opt = getopt(argc, argv, "i:I:mso:aw")) != -1) {
+ while ((opt = getopt(argc, argv, "i:I:mso:awM:K:")) != -1) {
switch(opt) {
case 'i':
kernel_read = optarg;
@@ -1683,6 +1853,12 @@ int main(int argc, char **argv)
case 'w':
warn_unresolved = 1;
break;
+ case 'M':
+ markers_write = optarg;
+ break;
+ case 'K':
+ markers_read = optarg;
+ break;
default:
exit(1);
}
@@ -1724,5 +1900,11 @@ int main(int argc, char **argv)
if (dump_write)
write_dump(dump_write);

+ if (markers_read)
+ read_markers(markers_read);
+
+ if (markers_write)
+ write_markers(markers_write);
+
return err;
}
diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
index 0ffed17..175301a 100644
--- a/scripts/mod/modpost.h
+++ b/scripts/mod/modpost.h
@@ -110,6 +110,8 @@ struct module {
int has_init;
int has_cleanup;
struct buffer dev_table_buf;
+ char **markers;
+ size_t nmarkers;
char srcversion[25];
};

@@ -124,6 +126,7 @@ struct elf_info {
Elf_Section export_gpl_sec;
Elf_Section export_unused_gpl_sec;
Elf_Section export_gpl_future_sec;
+ Elf_Section markers_strings_sec;
const char *strtab;
char *modinfo;
unsigned int modinfo_len;