[RFC PATCH v2 11/20] objtool: arm64: Walk instructions and compute CFI for each instruction

madvenka
2022-05-24T00:17:55Z

Implement arch_initial_func_cfi_state() to initialize the CFI for a
function.

Add code to fpv_decode() to walk the instructions in every function and
compute the CFI information for each instruction.

Implement special handling for cases like jump tables.

Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
---
tools/objtool/arch/arm64/decode.c | 15 +++
tools/objtool/fpv.c | 204 ++++++++++++++++++++++++++++++
2 files changed, 219 insertions(+)

diff --git a/tools/objtool/arch/arm64/decode.c b/tools/objtool/arch/arm64/decode.c
index f9df8b321659..93ef7c0811f1 100644
--- a/tools/objtool/arch/arm64/decode.c
+++ b/tools/objtool/arch/arm64/decode.c
@@ -35,6 +35,21 @@ struct decode {

/* --------------------- arch support functions ------------------------- */

+void arch_initial_func_cfi_state(struct cfi_init_state *state)
+{
+ int i;
+
+ for (i = 0; i < CFI_NUM_REGS; i++) {
+ state->regs[i].base = CFI_UNDEFINED;
+ state->regs[i].offset = 0;
+ }
+ state->regs[CFI_FP].base = CFI_CFA;
+
+ /* initial CFA (call frame address) */
+ state->cfa.base = CFI_SP;
+ state->cfa.offset = 0;
+}
+
unsigned long arch_dest_reloc_offset(int addend)
{
return addend;
diff --git a/tools/objtool/fpv.c b/tools/objtool/fpv.c
index 92ad0d0aac8e..52f613ae998f 100644
--- a/tools/objtool/fpv.c
+++ b/tools/objtool/fpv.c
@@ -13,6 +13,8 @@
#include <objtool/insn.h>
#include <objtool/warn.h>

+static bool fill;
+
/*
* Find the destination instructions for all jumps.
*/
@@ -50,15 +52,217 @@ static void add_jump_destinations(struct objtool_file *file)
}
}

+static void update_cfi_state(struct cfi_state *cfi, struct stack_op *op)
+{
+ struct cfi_reg *cfa = &cfi->cfa;
+ struct cfi_reg *regs = cfi->regs;
+
+ if (op->src.reg == CFI_SP) {
+ if (op->dest.reg == CFI_SP)
+ cfa->offset -= op->src.offset;
+ else
+ regs[CFI_FP].offset = -cfa->offset + op->src.offset;
+ } else {
+ if (op->dest.reg == CFI_SP)
+ cfa->offset = -(regs[CFI_FP].offset + op->src.offset);
+ else
+ regs[CFI_FP].offset += op->src.offset;
+ }
+
+ if (cfa->offset < -regs[CFI_FP].offset)
+ regs[CFI_FP].offset = 0;
+}
+
+static void do_stack_ops(struct instruction *insn, struct insn_state *state)
+{
+ struct stack_op *op;
+
+ list_for_each_entry(op, &insn->stack_ops, list) {
+ update_cfi_state(&state->cfi, op);
+ }
+}
+
+static void walk_code(struct objtool_file *file, struct section *sec,
+ struct symbol *func,
+ struct instruction *insn, struct insn_state *state)
+{
+ struct symbol *insn_func = insn->func;
+ struct instruction *dest;
+ struct cfi_state save_cfi;
+ unsigned long start, end;
+
+ for (; insn; insn = next_insn_same_sec(file, insn)) {
+
+ if (insn->func != insn_func)
+ return;
+
+ if (insn->cfi) {
+ if (fill) {
+ /* CFI is present. Nothing to fill. */
+ return;
+ }
+ if (insn->cfi->regs[CFI_FP].offset ||
+ !state->cfi.regs[CFI_FP].offset) {
+ return;
+ }
+ /*
+ * The new CFI contains a valid frame and the existing
+ * CFI doesn't. Replace the existing CFI with the new
+ * one.
+ */
+ }
+ insn->cfi = cfi_hash_find_or_add(&state->cfi);
+ dest = insn->jump_dest;
+
+ do_stack_ops(insn, state);
+
+ switch (insn->type) {
+ case INSN_BUG:
+ case INSN_RETURN:
+ case INSN_UNRELIABLE:
+ return;
+
+ case INSN_CALL:
+ case INSN_CALL_DYNAMIC:
+ start = func->offset;
+ end = start + func->len;
+ /*
+ * Treat intra-function calls as jumps and fall
+ * through.
+ */
+ if (!dest || dest->sec != sec ||
+ dest->offset <= start || dest->offset >= end) {
+ break;
+ }
+ /* fallthrough */
+
+ case INSN_JUMP_UNCONDITIONAL:
+ case INSN_JUMP_CONDITIONAL:
+ case INSN_JUMP_DYNAMIC:
+ if (dest) {
+ save_cfi = state->cfi;
+ walk_code(file, sec, func, dest, state);
+ state->cfi = save_cfi;
+ }
+ if (insn->type == INSN_JUMP_UNCONDITIONAL ||
+ insn->type == INSN_JUMP_DYNAMIC) {
+ return;
+ }
+ break;
+
+ default:
+ break;
+ }
+ }
+}
+
+static void walk_function(struct objtool_file *file, struct section *sec,
+ struct symbol *func)
+{
+ struct instruction *insn = find_insn(file, sec, func->offset);
+ struct insn_state state;
+
+ init_insn_state(&state, sec);
+ set_func_state(&state.cfi);
+
+ walk_code(file, sec, func, insn, &state);
+}
+
+/*
+ * This function addresses cases like jump tables where there is an array
+ * of unconditional branches. The normal walk would not have visited these
+ * instructions and established CFIs for them. Find those instructions. For
+ * each such instruction, copy the CFI from the branch instruction and
+ * propagate it down.
+ */
+static void fill_function(struct objtool_file *file, struct section *sec,
+ struct symbol *func)
+{
+ struct instruction *insn, *prev;
+ struct insn_state state;
+
+ func_for_each_insn(file, func, insn) {
+
+ if (insn->cfi) {
+ /* Instruction already has a CFI. */
+ continue;
+ }
+
+ prev = list_prev_entry(insn, list);
+ if (!prev || !prev->cfi) {
+ /*
+ * Previous instruction does not have a CFI that can
+ * be used for this instruction.
+ */
+ continue;
+ }
+
+ if (prev->type != INSN_JUMP_UNCONDITIONAL &&
+ prev->type != INSN_JUMP_DYNAMIC) {
+ /* Only copy CFI from unconditional branches. */
+ continue;
+ }
+
+ /*
+ * Propagate the CFI to all the instructions that can be
+ * visited from the current instruction that don't already
+ * have a CFI.
+ */
+ state.cfi = *prev->cfi;
+ walk_code(file, insn->sec, insn->func, insn, &state);
+ }
+}
+
+static void walk_section(struct objtool_file *file, struct section *sec)
+{
+ struct symbol *func;
+
+ list_for_each_entry(func, &sec->symbol_list, list) {
+
+ if (func->type != STT_FUNC || !func->len ||
+ func->pfunc != func || func->alias != func) {
+ /* No CFI generated for this function. */
+ continue;
+ }
+
+ if (!fill)
+ walk_function(file, sec, func);
+ else
+ fill_function(file, sec, func);
+ }
+}
+
+static void walk_sections(struct objtool_file *file)
+{
+ struct section *sec;
+
+ for_each_sec(file, sec) {
+ if (sec->sh.sh_flags & SHF_EXECINSTR)
+ walk_section(file, sec);
+ }
+}
+
int fpv_decode(struct objtool_file *file)
{
int ret;

+ arch_initial_func_cfi_state(&initial_func_cfi);
+
+ if (!cfi_hash_alloc(1UL << (file->elf->symbol_bits - 3)))
+ return -1;
+
ret = decode_instructions(file);
if (ret)
return ret;

add_jump_destinations(file);

+ if (!list_empty(&file->insn_list)) {
+ fill = false;
+ walk_sections(file);
+ fill = true;
+ walk_sections(file);
+ }
+
return 0;
}
--
2.25.1