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kgdbts: Switch to do_sys_openat2() for breakpoint testing

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Currently kgdbts can get stuck waiting for do_sys_open() to be called
in some of the current tests. This is because C compilers often
automatically inline this function, which is a very thin wrapper around
do_sys_openat2(), into some of its callers. gcc-10 does this on (at least)
both x86 and arm64.

We can fix the test suite by placing the breakpoints on do_sys_openat2()
instead since that isn't (currently) inlined. However do_sys_openat2() is
a static function so we cannot simply use an addressof. Since we are
testing debug machinery it is acceptable to use kallsyms to lookup a
suitable address because this is more or less what kdb does in the same
circumstances. Re-implement lookup_addr() to be based on kallsyms rather
than function pointers.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20210325094807.3546702-1-daniel.thompson@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Daniel Thompson 2021-03-25 09:48:07 +00:00 committed by Greg Kroah-Hartman
parent dbdc671d5c
commit 1114ab22e4
1 changed files with 28 additions and 18 deletions
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46
drivers/misc/kgdbts.c
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@ -92,6 +92,7 @@
#include <linux/kthread.h>
#include <linux/module.h>
#include <linux/sched/task.h>
#include <linux/kallsyms.h>
#include <asm/sections.h>
@ -200,21 +201,30 @@ static noinline void kgdbts_break_test(void)
v2printk("kgdbts: breakpoint complete\n");
}
/* Lookup symbol info in the kernel */
/*
* This is a cached wrapper for kallsyms_lookup_name().
*
* The cache is a big win for several tests. For example it more the doubles
* the cycles per second during the sys_open test. This is not theoretic,
* the performance improvement shows up at human scale, especially when
* testing using emulators.
*
* Obviously neither re-entrant nor thread-safe but that is OK since it
* can only be called from the debug trap (and therefore all other CPUs
* are halted).
*/
static unsigned long lookup_addr(char *arg)
{
unsigned long addr = 0;
static char cached_arg[KSYM_NAME_LEN];
static unsigned long cached_addr;
if (!strcmp(arg, "kgdbts_break_test"))
addr = (unsigned long)kgdbts_break_test;
else if (!strcmp(arg, "sys_open"))
addr = (unsigned long)do_sys_open;
else if (!strcmp(arg, "kernel_clone"))
addr = (unsigned long)kernel_clone;
else if (!strcmp(arg, "hw_break_val"))
addr = (unsigned long)&hw_break_val;
addr = (unsigned long) dereference_function_descriptor((void *)addr);
return addr;
if (strcmp(arg, cached_arg)) {
strscpy(cached_arg, arg, KSYM_NAME_LEN);
cached_addr = kallsyms_lookup_name(arg);
}
return (unsigned long)dereference_function_descriptor(
(void *)cached_addr);
}
static void break_helper(char *bp_type, char *arg, unsigned long vaddr)
@ -310,7 +320,7 @@ static int check_and_rewind_pc(char *put_str, char *arg)
if (arch_needs_sstep_emulation && sstep_addr &&
ip + offset == sstep_addr &&
((!strcmp(arg, "sys_open") || !strcmp(arg, "kernel_clone")))) {
((!strcmp(arg, "do_sys_openat2") || !strcmp(arg, "kernel_clone")))) {
/* This is special case for emulated single step */
v2printk("Emul: rewind hit single step bp\n");
restart_from_top_after_write = 1;
@ -619,14 +629,14 @@ static struct test_struct do_kernel_clone_test[] = {
*/
static struct test_struct sys_open_test[] = {
{ "?", "S0*" }, /* Clear break points */
{ "sys_open", "OK", sw_break, }, /* set sw breakpoint */
{ "do_sys_openat2", "OK", sw_break, }, /* set sw breakpoint */
{ "c", "T0*", NULL, get_thread_id_continue }, /* Continue */
{ "sys_open", "OK", sw_rem_break }, /*remove breakpoint */
{ "g", "sys_open", NULL, check_and_rewind_pc }, /* check location */
{ "do_sys_openat2", "OK", sw_rem_break }, /*remove breakpoint */
{ "g", "do_sys_openat2", NULL, check_and_rewind_pc }, /* check location */
{ "write", "OK", write_regs, emul_reset }, /* Write registers */
{ "s", "T0*", emul_sstep_get, emul_sstep_put }, /* Single step */
{ "g", "sys_open", NULL, check_single_step },
{ "sys_open", "OK", sw_break, }, /* set sw breakpoint */
{ "g", "do_sys_openat2", NULL, check_single_step },
{ "do_sys_openat2", "OK", sw_break, }, /* set sw breakpoint */
{ "7", "T0*", skip_back_repeat_test }, /* Loop based on repeat_test */
{ "D", "OK", NULL, final_ack_set }, /* detach and unregister I/O */
{ "", "", get_cont_catch, put_cont_catch },