[PATCH 18/22] objtool: Refactor jump table code
From: Josh Poimboeuf
Date: Sun Jul 14 2019 - 20:38:00 EST
Now that C jump tables are supported, call them "jump tables" instead of
"switch tables". Also rename some other variables, add comments, and
simplify the code flow a bit.
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
tools/objtool/check.c | 82 +++++++++++++++++++++++--------------------
tools/objtool/elf.c | 2 +-
tools/objtool/elf.h | 2 +-
3 files changed, 46 insertions(+), 40 deletions(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index a190a6e79a91..b21e9f7768d0 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -627,7 +627,7 @@ static int add_jump_destinations(struct objtool_file *file)
* 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 switch table.
+ * subfunction is through a switch jump table.
*/
if (!strstr(insn->func->name, ".cold.") &&
strstr(insn->jump_dest->func->name, ".cold.")) {
@@ -899,20 +899,24 @@ static int add_special_section_alts(struct objtool_file *file)
return ret;
}
-static int add_switch_table(struct objtool_file *file, struct instruction *insn,
+static int add_jump_table(struct objtool_file *file, struct instruction *insn,
struct rela *table, struct rela *next_table)
{
struct rela *rela = table;
- struct instruction *alt_insn;
+ struct instruction *dest_insn;
struct alternative *alt;
struct symbol *pfunc = insn->func->pfunc;
unsigned int prev_offset = 0;
- list_for_each_entry_from(rela, &table->rela_sec->rela_list, list) {
+ /*
+ * Each @rela is a switch table relocation which points to the target
+ * instruction.
+ */
+ list_for_each_entry_from(rela, &table->sec->rela_list, list) {
if (rela == next_table)
break;
- /* Make sure the switch table entries are consecutive: */
+ /* Make sure the table entries are consecutive: */
if (prev_offset && rela->offset != prev_offset + 8)
break;
@@ -921,12 +925,12 @@ static int add_switch_table(struct objtool_file *file, struct instruction *insn,
rela->addend == pfunc->offset)
break;
- alt_insn = find_insn(file, rela->sym->sec, rela->addend);
- if (!alt_insn)
+ dest_insn = find_insn(file, rela->sym->sec, rela->addend);
+ if (!dest_insn)
break;
- /* Make sure the jmp dest is in the function or subfunction: */
- if (alt_insn->func->pfunc != pfunc)
+ /* Make sure the destination is in the same function: */
+ if (dest_insn->func->pfunc != pfunc)
break;
alt = malloc(sizeof(*alt));
@@ -935,7 +939,7 @@ static int add_switch_table(struct objtool_file *file, struct instruction *insn,
return -1;
}
- alt->insn = alt_insn;
+ alt->insn = dest_insn;
list_add_tail(&alt->list, &insn->alts);
prev_offset = rela->offset;
}
@@ -950,7 +954,7 @@ static int add_switch_table(struct objtool_file *file, struct instruction *insn,
}
/*
- * find_switch_table() - Given a dynamic jump, find the switch jump table in
+ * find_jump_table() - Given a dynamic jump, find the switch jump table in
* .rodata associated with it.
*
* There are 3 basic patterns:
@@ -992,13 +996,13 @@ static int add_switch_table(struct objtool_file *file, struct instruction *insn,
*
* NOTE: RETPOLINE made it harder still to decode dynamic jumps.
*/
-static struct rela *find_switch_table(struct objtool_file *file,
+static struct rela *find_jump_table(struct objtool_file *file,
struct symbol *func,
struct instruction *insn)
{
- struct rela *text_rela, *rodata_rela;
+ struct rela *text_rela, *table_rela;
struct instruction *orig_insn = insn;
- struct section *rodata_sec;
+ struct section *table_sec;
unsigned long table_offset;
/*
@@ -1031,7 +1035,7 @@ static struct rela *find_switch_table(struct objtool_file *file,
continue;
table_offset = text_rela->addend;
- rodata_sec = text_rela->sym->sec;
+ table_sec = text_rela->sym->sec;
if (text_rela->type == R_X86_64_PC32)
table_offset += 4;
@@ -1045,29 +1049,31 @@ static struct rela *find_switch_table(struct objtool_file *file,
* need to be placed in the C_JUMP_TABLE_SECTION section. They
* have symbols associated with them.
*/
- if (find_symbol_containing(rodata_sec, table_offset) &&
- strcmp(rodata_sec->name, C_JUMP_TABLE_SECTION))
+ if (find_symbol_containing(table_sec, table_offset) &&
+ strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
continue;
- rodata_rela = find_rela_by_dest(rodata_sec, table_offset);
- if (rodata_rela) {
- /*
- * Use of RIP-relative switch jumps is quite rare, and
- * indicates a rare GCC quirk/bug which can leave dead
- * code behind.
- */
- if (text_rela->type == R_X86_64_PC32)
- file->ignore_unreachables = true;
+ /* Each table entry has a rela associated with it. */
+ table_rela = find_rela_by_dest(table_sec, table_offset);
+ if (!table_rela)
+ continue;
- return rodata_rela;
- }
+ /*
+ * Use of RIP-relative switch jumps is quite rare, and
+ * indicates a rare GCC quirk/bug which can leave dead code
+ * behind.
+ */
+ if (text_rela->type == R_X86_64_PC32)
+ file->ignore_unreachables = true;
+
+ return table_rela;
}
return NULL;
}
-static int add_func_switch_tables(struct objtool_file *file,
+static int add_func_jump_tables(struct objtool_file *file,
struct symbol *func)
{
struct instruction *insn, *last = NULL, *prev_jump = NULL;
@@ -1080,7 +1086,7 @@ static int add_func_switch_tables(struct objtool_file *file,
/*
* Store back-pointers for unconditional forward jumps such
- * that find_switch_table() can back-track using those and
+ * that find_jump_table() can back-track using those and
* avoid some potentially confusing code.
*/
if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
@@ -1095,17 +1101,17 @@ static int add_func_switch_tables(struct objtool_file *file,
if (insn->type != INSN_JUMP_DYNAMIC)
continue;
- rela = find_switch_table(file, func, insn);
+ rela = find_jump_table(file, func, insn);
if (!rela)
continue;
/*
- * We found a switch table, but we don't know yet how big it
+ * We found a jump table, but we don't know yet how big it
* is. Don't add it until we reach the end of the function or
- * the beginning of another switch table in the same function.
+ * the beginning of another jump table in the same function.
*/
if (prev_jump) {
- ret = add_switch_table(file, prev_jump, prev_rela, rela);
+ ret = add_jump_table(file, prev_jump, prev_rela, rela);
if (ret)
return ret;
}
@@ -1115,7 +1121,7 @@ static int add_func_switch_tables(struct objtool_file *file,
}
if (prev_jump) {
- ret = add_switch_table(file, prev_jump, prev_rela, NULL);
+ ret = add_jump_table(file, prev_jump, prev_rela, NULL);
if (ret)
return ret;
}
@@ -1128,7 +1134,7 @@ static int add_func_switch_tables(struct objtool_file *file,
* section which contains a list of addresses within the function to jump to.
* This finds these jump tables and adds them to the insn->alts lists.
*/
-static int add_switch_table_alts(struct objtool_file *file)
+static int add_jump_table_alts(struct objtool_file *file)
{
struct section *sec;
struct symbol *func;
@@ -1142,7 +1148,7 @@ static int add_switch_table_alts(struct objtool_file *file)
if (func->type != STT_FUNC)
continue;
- ret = add_func_switch_tables(file, func);
+ ret = add_func_jump_tables(file, func);
if (ret)
return ret;
}
@@ -1339,7 +1345,7 @@ static int decode_sections(struct objtool_file *file)
if (ret)
return ret;
- ret = add_switch_table_alts(file);
+ ret = add_jump_table_alts(file);
if (ret)
return ret;
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index d2c211b0a5a0..4650f5d3fff2 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -385,7 +385,7 @@ static int read_relas(struct elf *elf)
rela->offset = rela->rela.r_offset;
symndx = GELF_R_SYM(rela->rela.r_info);
rela->sym = find_symbol_by_index(elf, symndx);
- rela->rela_sec = sec;
+ rela->sec = sec;
if (!rela->sym) {
WARN("can't find rela entry symbol %d for %s",
symndx, sec->name);
diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h
index e44ca5d51871..1b638de4e7c0 100644
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -57,7 +57,7 @@ struct rela {
struct list_head list;
struct hlist_node hash;
GElf_Rela rela;
- struct section *rela_sec;
+ struct section *sec;
struct symbol *sym;
unsigned int type;
unsigned long offset;
--
2.20.1