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Message-ID: <70bf4b499941a6b19c5f750f5c36afcd6ffd216f.1746821544.git.jpoimboe@kernel.org>
Date: Fri, 9 May 2025 13:16:59 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
Petr Mladek <pmladek@...e.com>,
Miroslav Benes <mbenes@...e.cz>,
Joe Lawrence <joe.lawrence@...hat.com>,
live-patching@...r.kernel.org,
Song Liu <song@...nel.org>,
laokz <laokz@...mail.com>,
Jiri Kosina <jikos@...nel.org>,
Marcos Paulo de Souza <mpdesouza@...e.com>,
Weinan Liu <wnliu@...gle.com>,
Fazla Mehrab <a.mehrab@...edance.com>,
Chen Zhongjin <chenzhongjin@...wei.com>,
Puranjay Mohan <puranjay@...nel.org>
Subject: [PATCH v2 35/62] objtool: Refactor add_jump_destinations()
The add_jump_destinations() logic is a bit weird and convoluted after
being incrementally tweaked over the years. Refactor it to hopefully be
more logical and straightforward.
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
tools/objtool/check.c | 227 +++++++++++++---------------
tools/objtool/include/objtool/elf.h | 4 +-
2 files changed, 104 insertions(+), 127 deletions(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 66cbeebd16ea..e4ca5edf73ad 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1439,9 +1439,14 @@ static void add_return_call(struct objtool_file *file, struct instruction *insn,
}
static bool is_first_func_insn(struct objtool_file *file,
- struct instruction *insn, struct symbol *sym)
+ struct instruction *insn)
{
- if (insn->offset == sym->offset)
+ struct symbol *func = insn_func(insn);
+
+ if (!func)
+ return false;
+
+ if (insn->offset == func->offset)
return true;
/* Allow direct CALL/JMP past ENDBR */
@@ -1449,52 +1454,32 @@ static bool is_first_func_insn(struct objtool_file *file,
struct instruction *prev = prev_insn_same_sym(file, insn);
if (prev && prev->type == INSN_ENDBR &&
- insn->offset == sym->offset + prev->len)
+ insn->offset == func->offset + prev->len)
return true;
}
return false;
}
-/*
- * A sibling call is a tail-call to another symbol -- to differentiate from a
- * recursive tail-call which is to the same symbol.
- */
-static bool jump_is_sibling_call(struct objtool_file *file,
- struct instruction *from, struct instruction *to)
-{
- struct symbol *fs = from->sym;
- struct symbol *ts = to->sym;
-
- /* Not a sibling call if from/to a symbol hole */
- if (!fs || !ts)
- return false;
-
- /* Not a sibling call if not targeting the start of a symbol. */
- if (!is_first_func_insn(file, to, ts))
- return false;
-
- /* Disallow sibling calls into STT_NOTYPE */
- if (is_notype_sym(ts))
- return false;
-
- /* Must not be self to be a sibling */
- return fs->pfunc != ts->pfunc;
-}
-
/*
* Find the destination instructions for all jumps.
*/
static int add_jump_destinations(struct objtool_file *file)
{
- struct instruction *insn, *jump_dest;
+ struct instruction *insn;
struct reloc *reloc;
- struct section *dest_sec;
- unsigned long dest_off;
int ret;
for_each_insn(file, insn) {
struct symbol *func = insn_func(insn);
+ struct instruction *dest_insn;
+ struct section *dest_sec;
+ struct symbol *dest_sym;
+ unsigned long dest_off;
+ bool dest_undef = false;
+
+ if (!is_static_jump(insn))
+ continue;
if (insn->jump_dest) {
/*
@@ -1503,129 +1488,121 @@ static int add_jump_destinations(struct objtool_file *file)
*/
continue;
}
- if (!is_static_jump(insn))
- continue;
reloc = insn_reloc(file, insn);
if (!reloc) {
dest_sec = insn->sec;
dest_off = arch_jump_destination(insn);
- } else if (is_sec_sym(reloc->sym)) {
+ } else if (is_undef_sym(reloc->sym)) {
+ dest_sym = reloc->sym;
+ dest_undef = true;
+ } else {
dest_sec = reloc->sym->sec;
- dest_off = arch_insn_adjusted_addend(insn, reloc);
- } else if (reloc->sym->retpoline_thunk) {
+ dest_off = reloc->sym->sym.st_value +
+ arch_insn_adjusted_addend(insn, reloc);
+ }
+
+ if (!dest_undef) {
+ dest_insn = find_insn(file, dest_sec, dest_off);
+ if (!dest_insn) {
+ struct symbol *sym = find_symbol_by_offset(dest_sec, dest_off);
+
+ /*
+ * retbleed_untrain_ret() jumps to
+ * __x86_return_thunk(), but objtool can't find
+ * the thunk's starting RET instruction,
+ * because the RET is also in the middle of
+ * another instruction. Objtool only knows
+ * about the outer instruction.
+ */
+ if (sym && sym->embedded_insn) {
+ add_return_call(file, insn, false);
+ continue;
+ }
+
+ /*
+ * GCOV/KCOV dead code can jump to the end of
+ * the function/section.
+ */
+ if (file->ignore_unreachables && func &&
+ dest_sec == insn->sec &&
+ dest_off == func->offset + func->len)
+ continue;
+
+ ERROR_INSN(insn, "can't find jump dest instruction at %s+0x%lx",
+ dest_sec->name, dest_off);
+ return -1;
+ }
+
+ dest_sym = dest_insn->sym;
+ if (!dest_sym)
+ goto set_jump_dest;
+ }
+
+ if (dest_sym->retpoline_thunk) {
ret = add_retpoline_call(file, insn);
if (ret)
return ret;
continue;
- } else if (reloc->sym->return_thunk) {
+ }
+
+ if (dest_sym->return_thunk) {
add_return_call(file, insn, true);
continue;
- } else if (func) {
- /*
- * External sibling call or internal sibling call with
- * STT_FUNC reloc.
- */
- ret = add_call_dest(file, insn, reloc->sym, true);
- if (ret)
- return ret;
- continue;
- } else if (reloc->sym->sec->idx) {
- dest_sec = reloc->sym->sec;
- dest_off = reloc->sym->sym.st_value +
- arch_dest_reloc_offset(reloc_addend(reloc));
- } else {
- /* non-func asm code jumping to another file */
- continue;
}
- jump_dest = find_insn(file, dest_sec, dest_off);
- if (!jump_dest) {
- struct symbol *sym = find_symbol_by_offset(dest_sec, dest_off);
-
- /*
- * This is a special case for retbleed_untrain_ret().
- * It jumps to __x86_return_thunk(), but objtool
- * can't find the thunk's starting RET
- * instruction, because the RET is also in the
- * middle of another instruction. Objtool only
- * knows about the outer instruction.
- */
- if (sym && sym->embedded_insn) {
- add_return_call(file, insn, false);
- continue;
- }
-
- /*
- * GCOV/KCOV dead code can jump to the end of the
- * function/section.
- */
- if (file->ignore_unreachables && func &&
- dest_sec == insn->sec &&
- dest_off == func->offset + func->len)
- continue;
-
- ERROR_INSN(insn, "can't find jump dest instruction at %s+0x%lx",
- dest_sec->name, dest_off);
- return -1;
- }
-
- /*
- * An intra-TU jump in retpoline.o might not have a relocation
- * for its jump dest, in which case the above
- * add_{retpoline,return}_call() didn't happen.
- */
- if (jump_dest->sym && jump_dest->offset == jump_dest->sym->offset) {
- if (jump_dest->sym->retpoline_thunk) {
- ret = add_retpoline_call(file, insn);
+ if (dest_undef) {
+ /* External symbol */
+ if (func) {
+ /* External sibling call */
+ ret = add_call_dest(file, insn, dest_sym, true);
if (ret)
return ret;
continue;
}
- if (jump_dest->sym->return_thunk) {
- add_return_call(file, insn, true);
- continue;
- }
+
+ /* Non-func asm code jumping to external symbol */
+ continue;
}
+ if (!insn->sym || insn->sym == dest_insn->sym)
+ goto set_jump_dest;
+
/*
- * Cross-function jump.
+ * Internal cross-function jump.
*/
- if (func && insn_func(jump_dest) && !func->cold &&
- insn_func(jump_dest)->cold) {
-
- /*
- * For GCC 8+, create parent/child links for any cold
- * subfunctions. This is _mostly_ redundant with a
- * similar initialization in read_symbols().
- *
- * If a function has aliases, we want the *first* such
- * function in the symbol table to be the subfunction's
- * parent. In that case we overwrite the
- * initialization done in read_symbols().
- *
- * However this code can't completely replace the
- * read_symbols() code because this doesn't detect the
- * case where the parent function's only reference to a
- * subfunction is through a jump table.
- */
- func->cfunc = insn_func(jump_dest);
- insn_func(jump_dest)->pfunc = func;
+ /*
+ * For GCC 8+, create parent/child links for any cold
+ * subfunctions. This is _mostly_ redundant with a
+ * similar initialization in read_symbols().
+ *
+ * If a function has aliases, we want the *first* such
+ * function in the symbol table to be the subfunction's
+ * parent. In that case we overwrite the
+ * initialization done in read_symbols().
+ *
+ * However this code can't completely replace the
+ * read_symbols() code because this doesn't detect the
+ * case where the parent function's only reference to a
+ * subfunction is through a jump table.
+ */
+ if (func && dest_sym->cold) {
+ func->cfunc = dest_sym;
+ dest_sym->pfunc = func;
+ goto set_jump_dest;
}
- if (jump_is_sibling_call(file, insn, jump_dest)) {
- /*
- * Internal sibling call without reloc or with
- * STT_SECTION reloc.
- */
- ret = add_call_dest(file, insn, insn_func(jump_dest), true);
+ if (is_first_func_insn(file, dest_insn)) {
+ /* Internal sibling call */
+ ret = add_call_dest(file, insn, dest_sym, true);
if (ret)
return ret;
continue;
}
- insn->jump_dest = jump_dest;
+set_jump_dest:
+ insn->jump_dest = dest_insn;
}
return 0;
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index 842faec1b9a9..74c7b84b5310 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -180,9 +180,9 @@ static inline unsigned int elf_text_rela_type(struct elf *elf)
return elf_addr_size(elf) == 4 ? R_TEXT32 : R_TEXT64;
}
-static inline bool sym_has_sec(struct symbol *sym)
+static inline bool is_undef_sym(struct symbol *sym)
{
- return sym->sec->idx;
+ return !sym->sec->idx;
}
static inline bool is_null_sym(struct symbol *sym)
--
2.49.0
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