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Subject[PATCH 5/7] exec: In setup_new_exec cache current in the local variable me

At least gcc 8.3 when generating code for x86_64 has a hard time
consolidating multiple calls to current aka get_current(), and winds
up unnecessarily rereading %gs:current_task several times in
setup_new_exec.

Caching the value of current in the local variable of me generates
slightly better and shorter assembly.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
fs/exec.c | 23 ++++++++++++-----------
1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 93e40f865523..8c3abafb9bb1 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1391,6 +1391,7 @@ EXPORT_SYMBOL(would_dump);

void setup_new_exec(struct linux_binprm * bprm)
{
+ struct task_struct *me = current;
/*
* Once here, prepare_binrpm() will not be called any more, so
* the final state of setuid/setgid/fscaps can be merged into the
@@ -1400,7 +1401,7 @@ void setup_new_exec(struct linux_binprm * bprm)

if (bprm->secureexec) {
/* Make sure parent cannot signal privileged process. */
- current->pdeath_signal = 0;
+ me->pdeath_signal = 0;

/*
* For secureexec, reset the stack limit to sane default to
@@ -1413,9 +1414,9 @@ void setup_new_exec(struct linux_binprm * bprm)
bprm->rlim_stack.rlim_cur = _STK_LIM;
}

- arch_pick_mmap_layout(current->mm, &bprm->rlim_stack);
+ arch_pick_mmap_layout(me->mm, &bprm->rlim_stack);

- current->sas_ss_sp = current->sas_ss_size = 0;
+ me->sas_ss_sp = me->sas_ss_size = 0;

/*
* Figure out dumpability. Note that this checking only of current
@@ -1431,18 +1432,18 @@ void setup_new_exec(struct linux_binprm * bprm)

arch_setup_new_exec();
perf_event_exec();
- __set_task_comm(current, kbasename(bprm->filename), true);
+ __set_task_comm(me, kbasename(bprm->filename), true);

/* Set the new mm task size. We have to do that late because it may
* depend on TIF_32BIT which is only updated in flush_thread() on
* some architectures like powerpc
*/
- current->mm->task_size = TASK_SIZE;
+ me->mm->task_size = TASK_SIZE;

/* An exec changes our domain. We are no longer part of the thread
group */
- WRITE_ONCE(current->self_exec_id, current->self_exec_id + 1);
- flush_signal_handlers(current, 0);
+ WRITE_ONCE(me->self_exec_id, me->self_exec_id + 1);
+ flush_signal_handlers(me, 0);

/*
* install the new credentials for this executable
@@ -1458,16 +1459,16 @@ void setup_new_exec(struct linux_binprm * bprm)
* wait until new credentials are committed
* by commit_creds() above
*/
- if (get_dumpable(current->mm) != SUID_DUMP_USER)
- perf_event_exit_task(current);
+ if (get_dumpable(me->mm) != SUID_DUMP_USER)
+ perf_event_exit_task(me);
/*
* cred_guard_mutex must be held at least to this point to prevent
* ptrace_attach() from altering our determination of the task's
* credentials; any time after this it may be unlocked.
*/
security_bprm_committed_creds(bprm);
- mutex_unlock(&current->signal->exec_update_mutex);
- mutex_unlock(&current->signal->cred_guard_mutex);
+ mutex_unlock(&me->signal->exec_update_mutex);
+ mutex_unlock(&me->signal->cred_guard_mutex);
}
EXPORT_SYMBOL(setup_new_exec);

--
2.20.1
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