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modpost: extract symbol versions from *.cmd files

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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@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM-14 (x86-64)
This commit is contained in:
Masahiro Yamada 2022-05-13 20:39:21 +09:00
parent 69c4cc99bb
commit f292d875d0
1 changed files with 131 additions and 48 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

179
scripts/mod/modpost.c
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@ -383,19 +383,10 @@ static struct symbol *sym_add_exported(const char *name, struct module *mod,
return s;
}
static void sym_set_crc(const char *name, unsigned int crc)
static void sym_set_crc(struct symbol *sym, unsigned int crc)
{
struct symbol *s = find_symbol(name);
/*
* Ignore stand-alone __crc_*, which might be auto-generated symbols
* such as __*_veneer in ARM ELF.
*/
if (!s)
return;
s->crc = crc;
s->crc_valid = true;
sym->crc = crc;
sym->crc_valid = true;
}
static void *grab_file(const char *filename, size_t *size)
@ -618,33 +609,6 @@ static int ignore_undef_symbol(struct elf_info *info, const char *symname)
return 0;
}
static void handle_modversion(const struct module *mod,
const struct elf_info *info,
const Elf_Sym *sym, const char *symname)
{
unsigned int crc;
if (sym->st_shndx == SHN_UNDEF) {
warn("EXPORT symbol \"%s\" [%s%s] version generation failed, symbol will not be versioned.\n"
"Is \"%s\" prototyped in <asm/asm-prototypes.h>?\n",
symname, mod->name, mod->is_vmlinux ? "" : ".ko",
symname);
return;
}
if (sym->st_shndx == SHN_ABS) {
crc = sym->st_value;
} else {
unsigned int *crcp;
/* symbol points to the CRC in the ELF object */
crcp = sym_get_data(info, sym);
crc = TO_NATIVE(*crcp);
}
sym_set_crc(symname, crc);
}
static void handle_symbol(struct module *mod, struct elf_info *info,
const Elf_Sym *sym, const char *symname)
{
@ -1952,6 +1916,104 @@ static char *remove_dot(char *s)
return s;
}
/*
* 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_find_with_module() may return NULL here.
* It typically occurs when CONFIG_TRIM_UNUSED_KSYMS=y.
* Since commit e1327a127703, genksyms calculates CRCs of all
* symbols, including trimmed ones. Ignore orphan CRCs.
*/
sym = sym_find_with_module(name, mod);
if (sym)
sym_set_crc(sym, crc);
}
free(buf);
}
/*
* The symbol versions (CRC) are recorded in the .*.cmd files.
* Parse them to retrieve CRCs for the current module.
*/
static void mod_set_crcs(struct module *mod)
{
char objlist[PATH_MAX];
char *buf, *p, *obj;
int ret;
if (mod->is_vmlinux) {
strcpy(objlist, ".vmlinux.objs");
} else {
/* objects for a module are listed in the *.mod file. */
ret = snprintf(objlist, sizeof(objlist), "%s.mod", mod->name);
if (ret >= sizeof(objlist)) {
error("%s: too long path was truncated\n", objlist);
return;
}
}
buf = read_text_file(objlist);
p = buf;
while ((obj = strsep(&p, "\n")) && obj[0])
extract_crcs_for_object(obj, mod);
free(buf);
}
static void read_symbols(const char *modname)
{
const char *symname;
@ -2012,9 +2074,6 @@ static void read_symbols(const char *modname)
if (strstarts(symname, "__kstrtabns_"))
sym_update_namespace(symname + strlen("__kstrtabns_"),
sym_get_data(&info, sym));
if (strstarts(symname, "__crc_"))
handle_modversion(mod, &info, sym,
symname + strlen("__crc_"));
}
// check for static EXPORT_SYMBOL_* functions && global vars
@ -2042,12 +2101,17 @@ static void read_symbols(const char *modname)
parse_elf_finish(&info);
/* Our trick to get versioning for module struct etc. - it's
* never passed as an argument to an exported function, so
* the automatic versioning doesn't pick it up, but it's really
* important anyhow */
if (modversions)
if (modversions) {
/*
* Our trick to get versioning for module struct etc. - it's
* never passed as an argument to an exported function, so
* the automatic versioning doesn't pick it up, but it's really
* important anyhow.
*/
sym_add_unresolved("module_layout", mod, false);
mod_set_crcs(mod);
}
}
static void read_symbols_from_files(const char *filename)
@ -2204,6 +2268,23 @@ static void add_header(struct buffer *b, struct module *mod)
buf_printf(b, "\nMODULE_INFO(staging, \"Y\");\n");
}
static void check_symversions(struct module *mod)
{
struct symbol *sym;
if (!modversions)
return;
list_for_each_entry(sym, &mod->exported_symbols, list) {
if (!sym->crc_valid) {
warn("EXPORT symbol \"%s\" [%s%s] version generation failed, symbol will not be versioned.\n"
"Is \"%s\" prototyped in <asm/asm-prototypes.h>?\n",
sym->name, mod->name, mod->is_vmlinux ? "" : ".ko",
sym->name);
}
}
}
/**
* Record CRCs for unresolved symbols
**/
@ -2419,7 +2500,7 @@ static void read_dump(const char *fname)
}
s = sym_add_exported(symname, mod, gpl_only);
s->is_static = false;
sym_set_crc(symname, crc);
sym_set_crc(s, crc);
sym_update_namespace(symname, namespace);
}
free(buf);
@ -2545,6 +2626,8 @@ int main(int argc, char **argv)
if (mod->from_dump)
continue;
check_symversions(mod);
if (!mod->is_vmlinux)
write_mod_c_file(mod);
}