From ddb5cdbafaaad6b99d7007ae1740403124502d03 Mon Sep 17 00:00:00 2001
From: Masahiro Yamada <masahiroy@kernel.org>
Date: Mon, 12 Jun 2023 00:50:52 +0900
Subject: kbuild: generate KSYMTAB entries by modpost
Commit 7b4537199a4a ("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 22823ab419d8 ("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 8651ec01daed ("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>
---
scripts/mod/modpost.c | 106 ++++++++++++++++++++++++++++++++++----------------
1 file changed, 73 insertions(+), 33 deletions(-)
(limited to 'scripts/mod/modpost.c')
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 403ba4d923f5..ce37e6de5df7 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -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;
--
cgit