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kbuild: generate KSYMTAB entries by modpost

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Commit 7b4537199a ("kbuild: link symbol CRCs at final link, removing
CONFIG_MODULE_REL_CRCS") made modpost output CRCs in the same way
whether the EXPORT_SYMBOL() is placed in *.c or *.S.

For further cleanups, this commit applies a similar approach to the
entire data structure of EXPORT_SYMBOL().

The EXPORT_SYMBOL() compilation is split into two stages.

When a source file is compiled, EXPORT_SYMBOL() will be converted into
a dummy symbol in the .export_symbol section.

For example,

    EXPORT_SYMBOL(foo);
    EXPORT_SYMBOL_NS_GPL(bar, BAR_NAMESPACE);

will be encoded into the following assembly code:

    .section ".export_symbol","a"
    __export_symbol_foo:
            .asciz ""                      /* license */
            .asciz ""                      /* name space */
            .balign 8
            .quad foo                      /* symbol reference */
    .previous

    .section ".export_symbol","a"
    __export_symbol_bar:
            .asciz "GPL"                   /* license */
            .asciz "BAR_NAMESPACE"         /* name space */
            .balign 8
            .quad bar                      /* symbol reference */
    .previous

They are mere markers to tell modpost the name, license, and namespace
of the symbols. They will be dropped from the final vmlinux and modules
because the *(.export_symbol) will go into /DISCARD/ in the linker script.

Then, modpost extracts all the information about EXPORT_SYMBOL() from the
.export_symbol section, and generates the final C code:

    KSYMTAB_FUNC(foo, "", "");
    KSYMTAB_FUNC(bar, "_gpl", "BAR_NAMESPACE");

KSYMTAB_FUNC() (or KSYMTAB_DATA() if it is data) is expanded to struct
kernel_symbol that will be linked to the vmlinux or a module.

With this change, EXPORT_SYMBOL() works in the same way for *.c and *.S
files, providing the following benefits.

[1] Deprecate EXPORT_DATA_SYMBOL()

In the old days, EXPORT_SYMBOL() was only available in C files. To export
a symbol in *.S, EXPORT_SYMBOL() was placed in a separate *.c file.
arch/arm/kernel/armksyms.c is one example written in the classic manner.

Commit 22823ab419 ("EXPORT_SYMBOL() for asm") removed this limitation.
Since then, EXPORT_SYMBOL() can be placed close to the symbol definition
in *.S files. It was a nice improvement.

However, as that commit mentioned, you need to use EXPORT_DATA_SYMBOL()
for data objects on some architectures.

In the new approach, modpost checks symbol's type (STT_FUNC or not),
and outputs KSYMTAB_FUNC() or KSYMTAB_DATA() accordingly.

There are only two users of EXPORT_DATA_SYMBOL:

  EXPORT_DATA_SYMBOL_GPL(empty_zero_page)    (arch/ia64/kernel/head.S)
  EXPORT_DATA_SYMBOL(ia64_ivt)               (arch/ia64/kernel/ivt.S)

They are transformed as follows and output into .vmlinux.export.c

  KSYMTAB_DATA(empty_zero_page, "_gpl", "");
  KSYMTAB_DATA(ia64_ivt, "", "");

The other EXPORT_SYMBOL users in ia64 assembly are output as
KSYMTAB_FUNC().

EXPORT_DATA_SYMBOL() is now deprecated.

[2] merge <linux/export.h> and <asm-generic/export.h>

There are two similar header implementations:

  include/linux/export.h        for .c files
  include/asm-generic/export.h  for .S files

Ideally, the functionality should be consistent between them, but they
tend to diverge.

Commit 8651ec01da ("module: add support for symbol namespaces.") did
not support the namespace for *.S files.

This commit shifts the essential implementation part to C, which supports
EXPORT_SYMBOL_NS() for *.S files.

<asm/export.h> and <asm-generic/export.h> will remain as a wrapper of
<linux/export.h> for a while.

They will be removed after #include <asm/export.h> directives are all
replaced with #include <linux/export.h>.

[3] Implement CONFIG_TRIM_UNUSED_KSYMS in one-pass algorithm (by a later commit)

When CONFIG_TRIM_UNUSED_KSYMS is enabled, Kbuild recursively traverses
the directory tree to determine which EXPORT_SYMBOL to trim. If an
EXPORT_SYMBOL turns out to be unused by anyone, Kbuild begins the
second traverse, where some source files are recompiled with their
EXPORT_SYMBOL() tuned into a no-op.

We can do this better now; modpost can selectively emit KSYMTAB entries
that are really used by modules.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
This commit is contained in:
Masahiro Yamada
2023-06-12 00:50:52 +09:00
parent 94d6cb6812
commit ddb5cdbafa
12 changed files with 190 additions and 184 deletions
Download Patch File Download Diff File Expand all files Collapse all files

106
scripts/mod/modpost.c
View File

@@ -217,6 +217,7 @@ struct symbol {
unsigned int crc;
bool crc_valid;
bool weak;
bool is_func;
bool is_gpl_only; /* exported by EXPORT_SYMBOL_GPL */
char name[];
};
@@ -533,6 +534,8 @@ static int parse_elf(struct elf_info *info, const char *filename)
fatal("%s has NOBITS .modinfo\n", filename);
info->modinfo = (void *)hdr + sechdrs[i].sh_offset;
info->modinfo_len = sechdrs[i].sh_size;
} else if (!strcmp(secname, ".export_symbol")) {
info->export_symbol_secndx = i;
}
if (sechdrs[i].sh_type == SHT_SYMTAB) {
@@ -655,18 +658,6 @@ static void handle_symbol(struct module *mod, struct elf_info *info,
ELF_ST_BIND(sym->st_info) == STB_WEAK);
break;
default:
/* All exported symbols */
if (strstarts(symname, "__ksymtab_")) {
const char *name, *secname;
name = symname + strlen("__ksymtab_");
secname = sec_name(info, get_secindex(info, sym));
if (strstarts(secname, "___ksymtab_gpl+"))
sym_add_exported(name, mod, true);
else if (strstarts(secname, "___ksymtab+"))
sym_add_exported(name, mod, false);
}
if (strcmp(symname, "init_module") == 0)
mod->has_init = true;
if (strcmp(symname, "cleanup_module") == 0)
@@ -848,7 +839,6 @@ enum mismatch {
XXXEXIT_TO_SOME_EXIT,
ANY_INIT_TO_ANY_EXIT,
ANY_EXIT_TO_ANY_INIT,
EXPORT_TO_INIT_EXIT,
EXTABLE_TO_NON_TEXT,
};
@@ -920,12 +910,6 @@ static const struct sectioncheck sectioncheck[] = {
.bad_tosec = { INIT_SECTIONS, NULL },
.mismatch = ANY_INIT_TO_ANY_EXIT,
},
/* Do not export init/exit functions or data */
{
.fromsec = { "___ksymtab*", NULL },
.bad_tosec = { INIT_SECTIONS, EXIT_SECTIONS, NULL },
.mismatch = EXPORT_TO_INIT_EXIT,
},
{
.fromsec = { "__ex_table", NULL },
/* If you're adding any new black-listed sections in here, consider
@@ -1180,10 +1164,6 @@ static void default_mismatch_handler(const char *modname, struct elf_info *elf,
warn("%s: section mismatch in reference: %s (section: %s) -> %s (section: %s)\n",
modname, fromsym, fromsec, tosym, tosec);
break;
case EXPORT_TO_INIT_EXIT:
warn("%s: EXPORT_SYMBOL used for init/exit symbol: %s (section: %s)\n",
modname, tosym, tosec);
break;
case EXTABLE_TO_NON_TEXT:
warn("%s(%s+0x%lx): Section mismatch in reference to the %s:%s\n",
modname, fromsec, (long)faddr, tosec, tosym);
@@ -1211,14 +1191,75 @@ static void default_mismatch_handler(const char *modname, struct elf_info *elf,
}
}
static void check_export_symbol(struct module *mod, struct elf_info *elf,
Elf_Addr faddr, const char *secname,
Elf_Sym *sym)
{
static const char *prefix = "__export_symbol_";
const char *label_name, *name, *data;
Elf_Sym *label;
struct symbol *s;
bool is_gpl;
label = find_fromsym(elf, faddr, elf->export_symbol_secndx);
label_name = sym_name(elf, label);
if (!strstarts(label_name, prefix)) {
error("%s: .export_symbol section contains strange symbol '%s'\n",
mod->name, label_name);
return;
}
name = sym_name(elf, sym);
if (strcmp(label_name + strlen(prefix), name)) {
error("%s: .export_symbol section references '%s', but it does not seem to be an export symbol\n",
mod->name, name);
return;
}
data = sym_get_data(elf, label); /* license */
if (!strcmp(data, "GPL")) {
is_gpl = true;
} else if (!strcmp(data, "")) {
is_gpl = false;
} else {
error("%s: unknown license '%s' was specified for '%s'\n",
mod->name, data, name);
return;
}
data += strlen(data) + 1; /* namespace */
s = sym_add_exported(name, mod, is_gpl);
sym_update_namespace(name, data);
/*
* We need to be aware whether we are exporting a function or
* a data on some architectures.
*/
s->is_func = (ELF_ST_TYPE(sym->st_info) == STT_FUNC);
if (match(secname, PATTERNS(INIT_SECTIONS)))
warn("%s: %s: EXPORT_SYMBOL used for init symbol. Remove __init or EXPORT_SYMBOL.\n",
mod->name, name);
else if (match(secname, PATTERNS(EXIT_SECTIONS)))
warn("%s: %s: EXPORT_SYMBOL used for exit symbol. Remove __exit or EXPORT_SYMBOL.\n",
mod->name, name);
}
static void check_section_mismatch(struct module *mod, struct elf_info *elf,
Elf_Sym *sym,
unsigned int fsecndx, const char *fromsec,
Elf_Addr faddr, Elf_Addr taddr)
{
const char *tosec = sec_name(elf, get_secindex(elf, sym));
const struct sectioncheck *mismatch = section_mismatch(fromsec, tosec);
const struct sectioncheck *mismatch;
if (elf->export_symbol_secndx == fsecndx) {
check_export_symbol(mod, elf, faddr, tosec, sym);
return;
}
mismatch = section_mismatch(fromsec, tosec);
if (!mismatch)
return;
@@ -1698,15 +1739,6 @@ static void read_symbols(const char *modname)
handle_moddevtable(mod, &info, sym, symname);
}
for (sym = info.symtab_start; sym < info.symtab_stop; sym++) {
symname = remove_dot(info.strtab + sym->st_name);
/* Apply symbol namespaces from __kstrtabns_<symbol> entries. */
if (strstarts(symname, "__kstrtabns_"))
sym_update_namespace(symname + strlen("__kstrtabns_"),
sym_get_data(&info, sym));
}
check_sec_ref(mod, &info);
if (!mod->is_vmlinux) {
@@ -1890,6 +1922,14 @@ static void add_exported_symbols(struct buffer *buf, struct module *mod)
{
struct symbol *sym;
/* generate struct for exported symbols */
buf_printf(buf, "\n");
list_for_each_entry(sym, &mod->exported_symbols, list)
buf_printf(buf, "KSYMTAB_%s(%s, \"%s\", \"%s\");\n",
sym->is_func ? "FUNC" : "DATA", sym->name,
sym->is_gpl_only ? "_gpl" : "",
sym->namespace ?: "");
if (!modversions)
return;