Re: [PATCH] markers: modpost

Mathieu Desnoyers
2007-11-11T23:24:44Z

* David Smith (dsmith@redhat.com) wrote:
> Mathieu Desnoyers wrote:
> > Hrm, what would happen if a gcc optimization eventually decides to mix
> > the memory layout of the strings ? Is there something that specifies
> > that they won't ?
>
> Here's another patch that Roland wrote and I tested that
> attempts to solve the potential problem of string ordering
> by merging the name and format strings.
>

Yup, it looks good. I'll give it a try.

Thanks!

Mathieu

> ---
> 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 strings are made easy to extract by having the __trace_mark macro
> define the name and format together in a single array called __mstrtab_*
> in the __markers_strings section. This is straightforward and reliable
> as long as the marker structs are always defined by this macro. It is
> an unreasonable amount of hairy work to extract the string pointers from
> the __markers section structs, which entails handling a relocation type
> for every machine under the sun.
>
> Signed-off-by: Roland McGrath <roland@redhat.com>
> ---
> include/linux/marker.h | 9 +--
> scripts/Makefile.modpost | 11 +++
> scripts/mod/modpost.c | 163 +++++++++++++++++++++++++++++++++++++++++++++-
> scripts/mod/modpost.h | 3 +
> 4 files changed, 179 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/marker.h b/include/linux/marker.h
> index 5f36cf9..b978bbe 100644
> --- a/include/linux/marker.h
> +++ b/include/linux/marker.h
> @@ -51,15 +51,12 @@ struct marker {
> */
> #define __trace_mark(generic, name, call_data, format, args...) \
> do { \
> - static const char __mstrtab_name_##name[] \
> + static const char __mstrtab_##name[] \
> __attribute__((section("__markers_strings"))) \
> - = #name; \
> - static const char __mstrtab_format_##name[] \
> - __attribute__((section("__markers_strings"))) \
> - = format; \
> + = #name "\0" format; \
> static struct marker __mark_##name \
> __attribute__((section("__markers"), aligned(8))) = \
> - { __mstrtab_name_##name, __mstrtab_format_##name, \
> + { __mstrtab_##name, &__mstrtab_##name[sizeof(#name)], \
> 0, __mark_empty_function, NULL }; \
> __mark_check_format(format, ## args); \
> if (!generic) { \
> 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..53887e8 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 +1253,62 @@ 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;
> + size_t n;
> +
> + if (!info->markers_strings_sec)
> + return;
> +
> + /*
> + * First count the strings. We look for all the symbols defined
> + * in the __markers_strings section named __mstrtab_*. 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 &&
> + !strncmp(info->strtab + sym->st_name,
> + "__mstrtab_", sizeof "__mstrtab_" - 1)) {
> + if (first_sym == NULL)
> + first_sym = sym;
> + last_sym = sym;
> + ++n;
> + }
> +
> + if (n == 0)
> + return;
> +
> + /*
> + * Now collect each name and format into a 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));
> + mod->nmarkers = n;
> +
> + 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 &&
> + !strncmp(info->strtab + sym->st_name,
> + "__mstrtab_", sizeof "__mstrtab_" - 1)) {
> + const char *name = strings + sym->st_value;
> + const char *fmt = strchr(name, '\0') + 1;
> + char *line = NULL;
> + asprintf(&line, "%s\t%s\t%s\n", name, mod->name, fmt);
> + NOFAIL(line);
> + mod->markers[n++] = line;
> + }
> +}
> +
> static void read_symbols(char *modname)
> {
> const char *symname;
> @@ -1301,6 +1361,8 @@ 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 +1711,91 @@ 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 +1803,12 @@ 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 +1832,12 @@ 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 +1879,11 @@ 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;