[RFC PATCH v2 09/13] objtool: arm64: Decode LDR instructions

[Julien Thierry]

Load literal instructions can generate constants inside code sections.
Record the locations of the constants in order to be able to remove
their corresponding "struct instruction".

Signed-off-by: Julien Thierry <jthie...@redhat.com>
---
 tools/objtool/arch/arm64/decode.c    | 86 ++++++++++++++++++++++++++++
 tools/objtool/arch/x86/decode.c      |  5 ++
 tools/objtool/check.c                |  3 +
 tools/objtool/include/objtool/arch.h |  3 +
 4 files changed, 97 insertions(+)

diff --git a/tools/objtool/arch/arm64/decode.c 
b/tools/objtool/arch/arm64/decode.c
index 4e086d2251f5..b4631d79f13f 100644
--- a/tools/objtool/arch/arm64/decode.c
+++ b/tools/objtool/arch/arm64/decode.c
@@ -30,6 +30,73 @@ static unsigned long sign_extend(unsigned long x, int nbits)
        return ((~0UL + (sign_bit ^ 1)) << nbits) | x;
 }
 
+struct insn_loc {
+       const struct section *sec;
+       unsigned long offset;
+       struct hlist_node hnode;
+       bool ignorable;
+};
+
+DEFINE_HASHTABLE(invalid_insns, 16);
+
+static int record_invalid_insn(const struct section *sec,
+                              unsigned long offset,
+                              bool ignore)
+{
+       struct insn_loc *loc;
+       struct hlist_head *l;
+
+       l = &invalid_insns[hash_min(offset, HASH_BITS(invalid_insns))];
+       if (!hlist_empty(l)) {
+               loc = hlist_entry(l->first, struct insn_loc, hnode);
+               loc->ignorable |= ignore;
+               return 0;
+       }
+
+       loc = malloc(sizeof(*loc));
+       if (!loc) {
+               WARN("malloc failed");
+               return -1;
+       }
+
+       loc->sec = sec;
+       loc->offset = offset;
+       loc->ignorable = ignore;
+
+       hash_add(invalid_insns, &loc->hnode, loc->offset);
+
+       return 0;
+}
+
+int arch_post_process_instructions(struct objtool_file *file)
+{
+       struct hlist_node *tmp;
+       struct insn_loc *loc;
+       unsigned int bkt;
+       int res = 0;
+
+       hash_for_each_safe(invalid_insns, bkt, tmp, loc, hnode) {
+               struct instruction *insn;
+
+               insn = find_insn(file, (struct section *) loc->sec, 
loc->offset);
+               if (insn) {
+                       if (loc->ignorable) {
+                               list_del(&insn->list);
+                               hash_del(&insn->hash);
+                               free(insn);
+                       } else {
+                               WARN_FUNC("can't decode instruction", 
insn->sec, insn->offset);
+                               return -1;
+                       }
+               }
+
+               hash_del(&loc->hnode);
+               free(loc);
+       }
+
+       return res;
+}
+
 bool arch_callee_saved_reg(unsigned char reg)
 {
        switch (reg) {
@@ -389,6 +456,25 @@ int arch_decode_instruction(const struct elf *elf, const 
struct section *sec,
                if (ret <= 0)
                        return ret;
 
+               if (aarch64_insn_is_ldr_lit(insn)) {
+                       long pc_offset;
+
+                       pc_offset = insn & GENMASK(23, 5);
+                       /* Sign extend and multiply by 4 */
+                       pc_offset = (pc_offset << (64 - 23));
+                       pc_offset = ((pc_offset >> (64 - 23)) >> 5) << 2;
+
+                       if (record_invalid_insn(sec, offset + pc_offset, true))
+                               return -1;
+
+                       /* 64-bit literal */
+                       if (insn & BIT(30)) {
+                               if (record_invalid_insn(sec,
+                                                       offset + pc_offset + 4,
+                                                       true))
+                                       return -1;
+                       }
+               }
                *type = INSN_OTHER;
                break;
        }
diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 431bafb881d4..54f57bfd6f8f 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -619,6 +619,11 @@ int arch_decode_instruction(const struct elf *elf, const 
struct section *sec,
        return 0;
 }
 
+int arch_post_process_instructions(struct objtool_file *file)
+{
+       return 0;
+}
+
 void arch_initial_func_cfi_state(struct cfi_init_state *state)
 {
        int i;
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index a0f762a15ad5..7750f6342855 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -325,6 +325,9 @@ static int decode_instructions(struct objtool_file *file)
        if (stats)
                printf("nr_insns: %lu\n", nr_insns);
 
+       if (arch_post_process_instructions(file))
+               return -1;
+
        return 0;
 
 err:
diff --git a/tools/objtool/include/objtool/arch.h 
b/tools/objtool/include/objtool/arch.h
index ff21f387712d..6c61fc96ff00 100644
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -65,6 +65,7 @@ struct stack_op {
        struct list_head list;
 };
 
+struct objtool_file;
 struct instruction;
 
 void arch_initial_func_cfi_state(struct cfi_init_state *state);
@@ -75,6 +76,8 @@ int arch_decode_instruction(const struct elf *elf, const 
struct section *sec,
                            unsigned long *immediate,
                            struct list_head *ops_list);
 
+int arch_post_process_instructions(struct objtool_file *file);
+
 bool arch_callee_saved_reg(unsigned char reg);
 
 unsigned long arch_jump_destination(struct instruction *insn);
-- 
2.25.4