Message-ID: <20071108193617.GA31172@Krystal>
Date:	Thu, 8 Nov 2007 14:36:18 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	David Smith <dsmith@...hat.com>
Cc:	Roland McGrath <roland@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, systemtap@...rces.redhat.com
Subject: Re: [PATCH] markers: modpost

* David Smith (dsmith@...hat.com) wrote:
> Mathieu Desnoyers wrote:
> > * Roland McGrath (roland@...hat.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).
> 

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 ?

> 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@...hat.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;
> 
> 
> 
> 
> 

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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