Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull objtool fixes from Ingo Molnar: "A handful of objtool fixes: two improvements to how warnings are printed plus a false positive warning fix, and build environment fix" * 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: objtool: Fix Makefile to properly see if libelf is supported objtool: Detect falling through to the next function objtool: Add workaround for GCC switch jump table bug
This commit is contained in:
Linus Torvalds
commit
6527efba38
3 changed files with 103 additions and 35 deletions
3
Makefile
3
Makefile
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@ -1008,7 +1008,8 @@ prepare0: archprepare FORCE
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prepare: prepare0 prepare-objtool
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ifdef CONFIG_STACK_VALIDATION
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has_libelf := $(shell echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf - &> /dev/null && echo 1 || echo 0)
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has_libelf := $(call try-run,\
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echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf -,1,0)
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ifeq ($(has_libelf),1)
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objtool_target := tools/objtool FORCE
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else
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@ -299,18 +299,38 @@ they mean, and suggestions for how to fix them.
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Errors in .c files
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------------------
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If you're getting an objtool error in a compiled .c file, chances are
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the file uses an asm() statement which has a "call" instruction. An
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asm() statement with a call instruction must declare the use of the
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stack pointer in its output operand. For example, on x86_64:
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1. c_file.o: warning: objtool: funcA() falls through to next function funcB()
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register void *__sp asm("rsp");
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asm volatile("call func" : "+r" (__sp));
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This means that funcA() doesn't end with a return instruction or an
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unconditional jump, and that objtool has determined that the function
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can fall through into the next function. There could be different
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reasons for this:
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Otherwise the stack frame may not get created before the call.
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1) funcA()'s last instruction is a call to a "noreturn" function like
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panic(). In this case the noreturn function needs to be added to
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objtool's hard-coded global_noreturns array. Feel free to bug the
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objtool maintainer, or you can submit a patch.
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Another possible cause for errors in C code is if the Makefile removes
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-fno-omit-frame-pointer or adds -fomit-frame-pointer to the gcc options.
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2) funcA() uses the unreachable() annotation in a section of code
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that is actually reachable.
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3) If funcA() calls an inline function, the object code for funcA()
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might be corrupt due to a gcc bug. For more details, see:
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646
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2. If you're getting any other objtool error in a compiled .c file, it
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may be because the file uses an asm() statement which has a "call"
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instruction. An asm() statement with a call instruction must declare
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the use of the stack pointer in its output operand. For example, on
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x86_64:
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register void *__sp asm("rsp");
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asm volatile("call func" : "+r" (__sp));
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Otherwise the stack frame may not get created before the call.
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3. Another possible cause for errors in C code is if the Makefile removes
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-fno-omit-frame-pointer or adds -fomit-frame-pointer to the gcc options.
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Also see the above section for .S file errors for more information what
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the individual error messages mean.
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@ -54,6 +54,7 @@ struct instruction {
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struct symbol *call_dest;
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struct instruction *jump_dest;
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struct list_head alts;
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struct symbol *func;
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};
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struct alternative {
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@ -66,6 +67,7 @@ struct objtool_file {
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struct list_head insn_list;
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DECLARE_HASHTABLE(insn_hash, 16);
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struct section *rodata, *whitelist;
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bool ignore_unreachables, c_file;
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};
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const char *objname;
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@ -228,7 +230,7 @@ static int __dead_end_function(struct objtool_file *file, struct symbol *func,
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}
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}
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if (insn->type == INSN_JUMP_DYNAMIC)
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if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
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/* sibling call */
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return 0;
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}
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@ -248,6 +250,7 @@ static int dead_end_function(struct objtool_file *file, struct symbol *func)
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static int decode_instructions(struct objtool_file *file)
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{
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struct section *sec;
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struct symbol *func;
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unsigned long offset;
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struct instruction *insn;
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int ret;
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@ -281,6 +284,21 @@ static int decode_instructions(struct objtool_file *file)
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hash_add(file->insn_hash, &insn->hash, insn->offset);
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list_add_tail(&insn->list, &file->insn_list);
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}
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list_for_each_entry(func, &sec->symbol_list, list) {
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if (func->type != STT_FUNC)
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continue;
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if (!find_insn(file, sec, func->offset)) {
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WARN("%s(): can't find starting instruction",
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func->name);
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return -1;
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}
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func_for_each_insn(file, func, insn)
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if (!insn->func)
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insn->func = func;
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}
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}
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return 0;
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@ -664,13 +682,40 @@ static int add_func_switch_tables(struct objtool_file *file,
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text_rela->addend);
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/*
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* TODO: Document where this is needed, or get rid of it.
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*
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* rare case: jmpq *[addr](%rip)
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*
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* This check is for a rare gcc quirk, currently only seen in
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* three driver functions in the kernel, only with certain
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* obscure non-distro configs.
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*
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* As part of an optimization, gcc makes a copy of an existing
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* switch jump table, modifies it, and then hard-codes the jump
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* (albeit with an indirect jump) to use a single entry in the
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* table. The rest of the jump table and some of its jump
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* targets remain as dead code.
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*
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* In such a case we can just crudely ignore all unreachable
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* instruction warnings for the entire object file. Ideally we
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* would just ignore them for the function, but that would
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* require redesigning the code quite a bit. And honestly
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* that's just not worth doing: unreachable instruction
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* warnings are of questionable value anyway, and this is such
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* a rare issue.
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*
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* kbuild reports:
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* - https://lkml.kernel.org/r/201603231906.LWcVUpxm%25fengguang.wu@intel.com
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* - https://lkml.kernel.org/r/201603271114.K9i45biy%25fengguang.wu@intel.com
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* - https://lkml.kernel.org/r/201603291058.zuJ6ben1%25fengguang.wu@intel.com
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*
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* gcc bug:
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* - https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70604
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*/
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if (!rodata_rela)
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if (!rodata_rela) {
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rodata_rela = find_rela_by_dest(file->rodata,
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text_rela->addend + 4);
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if (rodata_rela)
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file->ignore_unreachables = true;
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}
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if (!rodata_rela)
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continue;
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@ -732,9 +777,6 @@ static int decode_sections(struct objtool_file *file)
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{
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int ret;
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file->whitelist = find_section_by_name(file->elf, "__func_stack_frame_non_standard");
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file->rodata = find_section_by_name(file->elf, ".rodata");
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ret = decode_instructions(file);
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if (ret)
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return ret;
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@ -799,6 +841,7 @@ static int validate_branch(struct objtool_file *file,
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struct alternative *alt;
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struct instruction *insn;
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struct section *sec;
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struct symbol *func = NULL;
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unsigned char state;
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int ret;
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@ -813,6 +856,16 @@ static int validate_branch(struct objtool_file *file,
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}
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while (1) {
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if (file->c_file && insn->func) {
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if (func && func != insn->func) {
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WARN("%s() falls through to next function %s()",
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func->name, insn->func->name);
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return 1;
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}
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func = insn->func;
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}
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if (insn->visited) {
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if (frame_state(insn->state) != frame_state(state)) {
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WARN_FUNC("frame pointer state mismatch",
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@ -823,13 +876,6 @@ static int validate_branch(struct objtool_file *file,
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return 0;
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}
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/*
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* Catch a rare case where a noreturn function falls through to
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* the next function.
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*/
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if (is_fentry_call(insn) && (state & STATE_FENTRY))
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return 0;
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insn->visited = true;
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insn->state = state;
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@ -1035,12 +1081,8 @@ static int validate_functions(struct objtool_file *file)
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continue;
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insn = find_insn(file, sec, func->offset);
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if (!insn) {
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WARN("%s(): can't find starting instruction",
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func->name);
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warnings++;
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if (!insn)
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continue;
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}
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ret = validate_branch(file, insn, 0);
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warnings += ret;
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@ -1056,13 +1098,14 @@ static int validate_functions(struct objtool_file *file)
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if (insn->visited)
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continue;
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if (!ignore_unreachable_insn(func, insn) &&
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!warnings) {
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WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
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warnings++;
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}
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insn->visited = true;
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if (file->ignore_unreachables || warnings ||
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ignore_unreachable_insn(func, insn))
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continue;
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WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
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warnings++;
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}
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}
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}
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@ -1133,6 +1176,10 @@ int cmd_check(int argc, const char **argv)
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INIT_LIST_HEAD(&file.insn_list);
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hash_init(file.insn_hash);
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file.whitelist = find_section_by_name(file.elf, "__func_stack_frame_non_standard");
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file.rodata = find_section_by_name(file.elf, ".rodata");
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file.ignore_unreachables = false;
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file.c_file = find_section_by_name(file.elf, ".comment");
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ret = decode_sections(&file);
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if (ret < 0)
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