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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Emit the .klp.symid table which allows "objtool klp diff" to reliably
* disambiguate duplicate-named local symbols in vmlinux.
*
* Livepatch identifies a duplicate-named symbol by its position (sympos)
* among the same-named kallsyms entries, counted in ascending address order
* in the final linked vmlinux. That order can't be derived from vmlinux.o
* alone: the final link reorders sub-sections (.text.unlikely*, .data..*,
* etc).
*
* Bridge the gap with a table which survives the final link: a single
* non-alloc section containing an array of { id, addr } entries, where
* 'id' is a unique counter identifier and 'addr' has a relocation to the
* symbol. The linker copies 'id' verbatim and resolves 'addr' to the symbol's
* final address.
*
* The table is only emitted for vmlinux.o, and only when klp-build asks for it
* with KLP_SYMIDS=1, which adds --klp-symids to the vmlinux.o objtool run.
*
* It can't survive --gc-sections, which sweeps the whole section; klp-build
* rejects CONFIG_LD_DEAD_CODE_DATA_ELIMINATION.
*/
#include <linux/string.h>
#include <objtool/objtool.h>
#include <objtool/warn.h>
#include <objtool/endianness.h>
#include <objtool/klp.h>
static const char * const discarded_secs[] = {
".discard",
".exitcall.exit",
".modinfo",
".no_trim_symbol",
"__tracepoint_check",
};
static bool discarded_sec(struct section *sec)
{
if (!(sec->sh.sh_flags & SHF_ALLOC))
return true;
for (int i = 0; i < ARRAY_SIZE(discarded_secs); i++)
if (strstarts(sec->name, discarded_secs[i]))
return true;
return false;
}
static bool symid_needed(struct elf *elf, struct symbol *sym)
{
struct symbol *s;
if (!is_local_sym(sym) || is_undef_sym(sym))
return false;
if (!is_func_sym(sym) && !is_object_sym(sym))
return false;
if (is_prefix_func(sym))
return false;
if (discarded_sec(sym->sec))
return false;
for_each_sym_by_name(elf, sym->name, s) {
if (s == sym || is_sec_sym(s) || is_file_sym(s) || is_undef_sym(s))
continue;
return true;
}
return false;
}
int klp_create_symid_sections(struct objtool_file *file)
{
struct elf *elf = file->elf;
struct klp_symid *symids;
struct section *sec;
struct symbol *sym;
u64 nr = 0, i = 0;
if (!str_ends_with(objname, "vmlinux.o"))
return 0;
for_each_sym(elf, sym)
if (symid_needed(elf, sym))
nr++;
if (!nr)
return 0;
sec = elf_create_section(elf, KLP_SYMID_SEC, 0, sizeof(struct klp_symid),
SHT_PROGBITS, 8, 0);
if (!sec)
return -1;
symids = elf_add_data(elf, sec, NULL, nr * sizeof(struct klp_symid));
if (!symids)
return -1;
for_each_sym(elf, sym) {
if (!symid_needed(elf, sym))
continue;
symids[i].id = bswap_if_needed(elf, i);
if (!elf_create_reloc(elf, sec,
i * sizeof(struct klp_symid) +
offsetof(struct klp_symid, addr),
sym, 0, R_ABS64))
return -1;
i++;
}
return 0;
}
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