Re: [PATCH] markers: modpost

Mathieu Desnoyers
2007-11-01T02:46:36Z

* Roland McGrath (roland@redhat.com) wrote:
>
> 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 very
> simple and should work fine in practice for the foreseeable future.
>

Hi Roland,

I'm ok with the idea of extracting such information, but I doubt one can
assume the strings will always be layed out in the same order in the
__markers_strings section. We also shouldn't assume that a marker name
will be a neighbor of its format string.

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 ?

Mathieu

> Signed-off-by: Roland McGrath <roland@redhat.com>
> ---
> scripts/Makefile.modpost | 11 +++
> scripts/mod/modpost.c | 174 +++++++++++++++++++++++++++++++++++++++++++++-
> scripts/mod/modpost.h | 3 +
> 3 files changed, 187 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..df80bfc 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 +1253,73 @@ static int exit_section_ref_ok(const char *name)
> return 0;
> }
>
> +static size_t strlen_with_padding(const char *start, const char *limit)
> +{
> + const char *p = memchr(start, '\0', limit - start);
> + if (p == NULL)
> + return 0;
> + do
> + ++p;
> + while (p < limit && *p == '\0');
> + return p - start;
> +}
> +
> +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 *strings_end;
> + const char *p;
> + size_t n, i;
> +
> + if (!info->markers_strings_sec)
> + return;
> +
> + strings = (const char *) info->hdr + sh->sh_offset;
> + strings_end = strings + sh->sh_size;
> +
> + /*
> + * First count the strings. They come in pairs of name, format.
> + */
> + for (n = 0, p = strings; p < strings_end; ++n) {
> + size_t len = strlen_with_padding(p, strings_end);
> + if (len == 0)
> + break;
> + p += len;
> + }
> + if (n % 2 != 0 || p != strings_end) {
> + 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.
> + */
> + mod->markers = NOFAIL(malloc(sizeof mod->markers[0] * n / 2));
> + mod->nmarkers = n / 2;
> +
> + p = strings;
> + for (i = 0; i < n; i += 2) {
> + const char *name, *fmt;
> + name = p;
> + p += strlen_with_padding(p, strings_end);
> + fmt = p;
> + p += strlen_with_padding(p, strings_end);
> +
> + mod->markers[i / 2] = NULL;
> + asprintf(&mod->markers[i / 2], "%s\t%s\t%s\n",
> + name, mod->name, fmt);
> + NOFAIL(mod->markers[i / 2]);
> + }
> +}
> +
> static void read_symbols(char *modname)
> {
> const char *symname;
> @@ -1301,6 +1372,8 @@ 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 +1722,91 @@ 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 +1814,12 @@ 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 +1843,12 @@ 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 +1890,11 @@ 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;