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objtool: Refactor jump table code 

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@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/cf951b0c0641628e0b9b81f7ceccd9bcabcb4bd8.1563413318.git.jpoimboe@redhat.com
This commit is contained in:
Josh Poimboeuf 2019-07-17 20:36:53 -05:00 committed by Thomas Gleixner
parent 0c1ddd3317
commit e7c2bc37bf
3 changed files with 46 additions and 40 deletions
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82
tools/objtool/check.c
View File

@ -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 jump table.
*/
if (!strstr(insn->func->name, ".cold.") &&
strstr(insn->jump_dest->func->name, ".cold.")) {
@ -899,20 +899,24 @@ out:
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;

2
tools/objtool/elf.c
View File

@ -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);

2
tools/objtool/elf.h
View File

@ -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;