On Thu, May 12, 2022 at 1:49 AM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote:
>
> Currently, CONFIG_MODVERSIONS needs extra link to embed the symbol
> versions into ELF objects. Then, modpost extracts the version CRCs
> from them.
>
> The following figures show how it currently works, and how I am trying
> to change it.
>
> Current implementation
> ======================
> |----------|
> embed CRC -------------------------->| final |
> $(CC) $(LD) / |---------| | link for |
> -----> *.o -------> *.o -->| modpost | | vmlinux |
> / / | |-- *.mod.c -->| or |
> / genksyms / |---------| | module |
> *.c ------> *.symversions |----------|
>
> Genksyms outputs the calculated CRCs in the form of linker script
> (*.symversions), which is used by $(LD) to update the object.
>
> If CONFIG_LTO_CLANG=y, the build process is much more complex. Embedding
> the CRCs is postponed until the LLVM bitcode is converted into ELF,
> creating another intermediate *.prelink.o.
>
> However, this complexity is unneeded. There is no reason why we must
> embed version CRCs in objects so early.
>
> There is final link stage for vmlinux (scripts/link-vmlinux.sh) and
> modules (scripts/Makefile.modfinal). We can link CRCs at the very last
> moment.
>
> New implementation
> ==================
> |----------|
> --------------------------------------->| final |
> $(CC) / |---------| | link for |
> -----> *.o ---->| | | vmlinux |
> / | modpost |--- .vmlinux.export.c -->| or |
> / genksyms | |--- *.mod.c ------------>| module |
> *.c ------> *.cmd -->|---------| |----------|
>
> Pass the symbol versions to modpost as separate text data, which are
> available in *.cmd files.
>
> This commit changes modpost to extract CRCs from *.cmd files instead of
> from ELF objects.
>
> Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> Reviewed-by: Nicolas Schier <nicolas@xxxxxxxxx>
> Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> Reviewed-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> ---
>
> (no changes since v2)
>
> Changes in v2:
> - Simplify the implementation (parse .cmd files after ELF)
>
> scripts/mod/modpost.c | 177 ++++++++++++++++++++++++++++++------------
> 1 file changed, 129 insertions(+), 48 deletions(-)
> +/*
> + * The CRCs are recorded in .*.cmd files in the form of:
> + * #SYMVER <name> <crc>
> + */
> +static void extract_crcs_for_object(const char *object, struct module *mod)
> +{
> + char cmd_file[PATH_MAX];
> + char *buf, *p;
> + const char *base;
> + int dirlen, ret;
> +
> + base = strrchr(object, '/');
> + if (base) {
> + base++;
> + dirlen = base - object;
> + } else {
> + dirlen = 0;
> + base = object;
> + }
> +
> + ret = snprintf(cmd_file, sizeof(cmd_file), "%.*s.%s.cmd",
> + dirlen, object, base);
> + if (ret >= sizeof(cmd_file)) {
> + error("%s: too long path was truncated\n", cmd_file);
> + return;
> + }
> +
> + buf = read_text_file(cmd_file);
> + p = buf;
> +
> + while ((p = strstr(p, "\n#SYMVER "))) {
> + char *name;
> + size_t namelen;
> + unsigned int crc;
> + struct symbol *sym;
> +
> + name = p + strlen("\n#SYMVER ");
> +
> + p = strchr(name, ' ');
> + if (!p)
> + break;
> +
> + namelen = p - name;
> + p++;
> +
> + if (!isdigit(*p))
> + continue; /* skip this line */
> +
> + crc = strtol(p, &p, 0);
> + if (*p != '\n')
> + continue; /* skip this line */
> +
> + name[namelen] = '\0';
> +
> + sym = sym_find_with_module(name, mod);
> + if (!sym) {
> + warn("Skip the version for unexported symbol \"%s\" [%s%s]\n",
> + name, mod->name, mod->is_vmlinux ? "" : ".ko");
> + continue;
> + }
A lot of warnings are displayed when CONFIG_TRIM_UNUSED_KSYMS=y.
I will fix this in v6.
--
Best Regards
Masahiro Yamada
