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SubjectRe: [PATCH v2 01/14] objtool: Tag retpoline thunk symbols
On Wed, Oct 20, 2021 at 08:17:14AM -0700, Josh Poimboeuf wrote:
> On Wed, Oct 20, 2021 at 12:44:43PM +0200, Peter Zijlstra wrote:
> > In order to avoid calling arch_is_retpoline() (which does a strcmp)
> > over and over on symbols, tag them once upfront.
> >
> > XXX do we also want to do __fentry__ ?
>
> Might as well.
>
> > XXX do we want an enum instead of a bunch of bools ?
>
> Maybe, or convert the bools to bit fields.

Like so then...

---
Subject: objtool: Classify symbols
From: Peter Zijlstra <peterz@infradead.org>
Date: Wed Oct 20 10:05:55 CEST 2021

In order to avoid calling str*cmp() on symbol names, over and over, do
them all once upfront and store the result.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
tools/objtool/check.c | 34 ++++++++++++++++++++++------------
tools/objtool/include/objtool/elf.h | 5 ++++-
2 files changed, 26 insertions(+), 13 deletions(-)

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1012,8 +1012,7 @@ static void add_call_dest(struct objtool
* so they need a little help, NOP out any KCOV calls from noinstr
* text.
*/
- if (insn->sec->noinstr &&
- !strncmp(insn->call_dest->name, "__sanitizer_cov_", 16)) {
+ if (insn->sec->noinstr && insn->call_dest->kcov) {
if (reloc) {
reloc->type = R_NONE;
elf_write_reloc(file->elf, reloc);
@@ -1027,7 +1026,7 @@ static void add_call_dest(struct objtool
insn->type = sibling ? INSN_RETURN : INSN_NOP;
}

- if (mcount && !strcmp(insn->call_dest->name, "__fentry__")) {
+ if (mcount && insn->call_dest->fentry) {
if (sibling)
WARN_FUNC("Tail call to __fentry__ !?!?", insn->sec, insn->offset);

@@ -1077,7 +1076,7 @@ static int add_jump_destinations(struct
} else if (reloc->sym->type == STT_SECTION) {
dest_sec = reloc->sym->sec;
dest_off = arch_dest_reloc_offset(reloc->addend);
- } else if (arch_is_retpoline(reloc->sym)) {
+ } else if (reloc->sym->retpoline_thunk) {
/*
* Retpoline jumps are really dynamic jumps in
* disguise, so convert them accordingly.
@@ -1218,7 +1217,7 @@ static int add_call_destinations(struct

add_call_dest(file, insn, dest, false);

- } else if (arch_is_retpoline(reloc->sym)) {
+ } else if (reloc->sym->retpoline_thunk) {
/*
* Retpoline calls are really dynamic calls in
* disguise, so convert them accordingly.
@@ -1919,17 +1918,28 @@ static int read_intra_function_calls(str
return 0;
}

-static int read_static_call_tramps(struct objtool_file *file)
+static int classify_symbols(struct objtool_file *file)
{
struct section *sec;
struct symbol *func;

for_each_sec(file, sec) {
list_for_each_entry(func, &sec->symbol_list, list) {
- if (func->bind == STB_GLOBAL &&
- !strncmp(func->name, STATIC_CALL_TRAMP_PREFIX_STR,
+ if (func->bind != STB_GLOBAL)
+ continue;
+
+ if (!strncmp(func->name, STATIC_CALL_TRAMP_PREFIX_STR,
strlen(STATIC_CALL_TRAMP_PREFIX_STR)))
func->static_call_tramp = true;
+
+ if (arch_is_retpoline(func))
+ func->retpoline_thunk = true;
+
+ if (!strcmp(func->name, "__fentry__"))
+ func->fentry = true;
+
+ if (!strncmp(func->name, "__sanitizer_cov_", 16))
+ func->kcov = true;
}
}

@@ -1995,7 +2005,7 @@ static int decode_sections(struct objtoo
/*
* Must be before add_{jump_call}_destination.
*/
- ret = read_static_call_tramps(file);
+ ret = classify_symbols(file);
if (ret)
return ret;

@@ -2053,9 +2063,9 @@ static int decode_sections(struct objtoo

static bool is_fentry_call(struct instruction *insn)
{
- if (insn->type == INSN_CALL && insn->call_dest &&
- insn->call_dest->type == STT_NOTYPE &&
- !strcmp(insn->call_dest->name, "__fentry__"))
+ if (insn->type == INSN_CALL &&
+ insn->call_dest &&
+ insn->call_dest->fentry)
return true;

return false;
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -55,7 +55,10 @@ struct symbol {
unsigned int len;
struct symbol *pfunc, *cfunc, *alias;
bool uaccess_safe;
- bool static_call_tramp;
+ u8 static_call_tramp : 1;
+ u8 retpoline_thunk : 1;
+ u8 fentry : 1;
+ u8 kcov : 1;
struct list_head pv_target;
};

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