| Message ID | 20200509214159.19680-2-liwei391@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: kgdb/kdb: Fix single-step debugging issues | expand |
Hi, On Sat, May 9, 2020 at 6:49 AM Wei Li <liwei391@huawei.com> wrote: > > After entering kdb due to breakpoint, when we execute 'ss' or 'go' (will > delay installing breakpoints, do single-step first), it won't work > correctly, and it will enter kdb due to oops. > > It's because the reason gotten in kdb_stub() is not as expected, and it > seems that the ex_vector for single-step should be 0, like what arch > powerpc/sh/parisc has implemented. > > Before the patch: > Entering kdb (current=0xffff8000119e2dc0, pid 0) on processor 0 due to Keyboard Entry > [0]kdb> bp printk > Instruction(i) BP #0 at 0xffff8000101486cc (printk) > is enabled addr at ffff8000101486cc, hardtype=0 installed=0 > > [0]kdb> g > > / # echo h > /proc/sysrq-trigger > > Entering kdb (current=0xffff0000fa878040, pid 266) on processor 3 due to Breakpoint @ 0xffff8000101486cc > [3]kdb> ss > > Entering kdb (current=0xffff0000fa878040, pid 266) on processor 3 Oops: (null) > due to oops @ 0xffff800010082ab8 > CPU: 3 PID: 266 Comm: sh Not tainted 5.7.0-rc4-13839-gf0e5ad491718 #6 > Hardware name: linux,dummy-virt (DT) > pstate: 00000085 (nzcv daIf -PAN -UAO) > pc : el1_irq+0x78/0x180 > lr : __handle_sysrq+0x80/0x190 > sp : ffff800015003bf0 > x29: ffff800015003d20 x28: ffff0000fa878040 > x27: 0000000000000000 x26: ffff80001126b1f0 > x25: ffff800011b6a0d8 x24: 0000000000000000 > x23: 0000000080200005 x22: ffff8000101486cc > x21: ffff800015003d30 x20: 0000ffffffffffff > x19: ffff8000119f2000 x18: 0000000000000000 > x17: 0000000000000000 x16: 0000000000000000 > x15: 0000000000000000 x14: 0000000000000000 > x13: 0000000000000000 x12: 0000000000000000 > x11: 0000000000000000 x10: 0000000000000000 > x9 : 0000000000000000 x8 : ffff800015003e50 > x7 : 0000000000000002 x6 : 00000000380b9990 > x5 : ffff8000106e99e8 x4 : ffff0000fadd83c0 > x3 : 0000ffffffffffff x2 : ffff800011b6a0d8 > x1 : ffff800011b6a000 x0 : ffff80001130c9d8 > Call trace: > el1_irq+0x78/0x180 > printk+0x0/0x84 > write_sysrq_trigger+0xb0/0x118 > proc_reg_write+0xb4/0xe0 > __vfs_write+0x18/0x40 > vfs_write+0xb0/0x1b8 > ksys_write+0x64/0xf0 > __arm64_sys_write+0x14/0x20 > el0_svc_common.constprop.2+0xb0/0x168 > do_el0_svc+0x20/0x98 > el0_sync_handler+0xec/0x1a8 > el0_sync+0x140/0x180 > > [3]kdb> > > After the patch: > Entering kdb (current=0xffff8000119e2dc0, pid 0) on processor 0 due to Keyboard Entry > [0]kdb> bp printk > Instruction(i) BP #0 at 0xffff8000101486cc (printk) > is enabled addr at ffff8000101486cc, hardtype=0 installed=0 > > [0]kdb> g > > / # echo h > /proc/sysrq-trigger > > Entering kdb (current=0xffff0000fa852bc0, pid 268) on processor 0 due to Breakpoint @ 0xffff8000101486cc > [0]kdb> g > > Entering kdb (current=0xffff0000fa852bc0, pid 268) on processor 0 due to Breakpoint @ 0xffff8000101486cc > [0]kdb> ss > > Entering kdb (current=0xffff0000fa852bc0, pid 268) on processor 0 due to SS trap @ 0xffff800010082ab8 > [0]kdb> > > Fixes: 44679a4f142b ("arm64: KGDB: Add step debugging support") > Signed-off-by: Wei Li <liwei391@huawei.com> > --- > arch/arm64/kernel/kgdb.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) As far as I can tell this looks right. Specifically in kdb_stub() I see that it needs "ks->ex_vector == 0" to get "reason" as KDB_REASON_SSTEP. Reviewed-by: Douglas Anderson <dianders@chromium.org> I did really basic testing of this series as a whole and things that used to be broken for me around stepping / going past breakpoints are now fixed. I'll keep using it more, but it definitely feels like it makes things happier. Tested-by: Douglas Anderson <dianders@chromium.org> -Doug
diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c index 43119922341f..1a157ca33262 100644 --- a/arch/arm64/kernel/kgdb.c +++ b/arch/arm64/kernel/kgdb.c @@ -252,7 +252,7 @@ static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned int esr) if (!kgdb_single_step) return DBG_HOOK_ERROR; - kgdb_handle_exception(1, SIGTRAP, 0, regs); + kgdb_handle_exception(0, SIGTRAP, 0, regs); return DBG_HOOK_HANDLED; } NOKPROBE_SYMBOL(kgdb_step_brk_fn);
After entering kdb due to breakpoint, when we execute 'ss' or 'go' (will delay installing breakpoints, do single-step first), it won't work correctly, and it will enter kdb due to oops. It's because the reason gotten in kdb_stub() is not as expected, and it seems that the ex_vector for single-step should be 0, like what arch powerpc/sh/parisc has implemented. Before the patch: Entering kdb (current=0xffff8000119e2dc0, pid 0) on processor 0 due to Keyboard Entry [0]kdb> bp printk Instruction(i) BP #0 at 0xffff8000101486cc (printk) is enabled addr at ffff8000101486cc, hardtype=0 installed=0 [0]kdb> g / # echo h > /proc/sysrq-trigger Entering kdb (current=0xffff0000fa878040, pid 266) on processor 3 due to Breakpoint @ 0xffff8000101486cc [3]kdb> ss Entering kdb (current=0xffff0000fa878040, pid 266) on processor 3 Oops: (null) due to oops @ 0xffff800010082ab8 CPU: 3 PID: 266 Comm: sh Not tainted 5.7.0-rc4-13839-gf0e5ad491718 #6 Hardware name: linux,dummy-virt (DT) pstate: 00000085 (nzcv daIf -PAN -UAO) pc : el1_irq+0x78/0x180 lr : __handle_sysrq+0x80/0x190 sp : ffff800015003bf0 x29: ffff800015003d20 x28: ffff0000fa878040 x27: 0000000000000000 x26: ffff80001126b1f0 x25: ffff800011b6a0d8 x24: 0000000000000000 x23: 0000000080200005 x22: ffff8000101486cc x21: ffff800015003d30 x20: 0000ffffffffffff x19: ffff8000119f2000 x18: 0000000000000000 x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000 x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000 x8 : ffff800015003e50 x7 : 0000000000000002 x6 : 00000000380b9990 x5 : ffff8000106e99e8 x4 : ffff0000fadd83c0 x3 : 0000ffffffffffff x2 : ffff800011b6a0d8 x1 : ffff800011b6a000 x0 : ffff80001130c9d8 Call trace: el1_irq+0x78/0x180 printk+0x0/0x84 write_sysrq_trigger+0xb0/0x118 proc_reg_write+0xb4/0xe0 __vfs_write+0x18/0x40 vfs_write+0xb0/0x1b8 ksys_write+0x64/0xf0 __arm64_sys_write+0x14/0x20 el0_svc_common.constprop.2+0xb0/0x168 do_el0_svc+0x20/0x98 el0_sync_handler+0xec/0x1a8 el0_sync+0x140/0x180 [3]kdb> After the patch: Entering kdb (current=0xffff8000119e2dc0, pid 0) on processor 0 due to Keyboard Entry [0]kdb> bp printk Instruction(i) BP #0 at 0xffff8000101486cc (printk) is enabled addr at ffff8000101486cc, hardtype=0 installed=0 [0]kdb> g / # echo h > /proc/sysrq-trigger Entering kdb (current=0xffff0000fa852bc0, pid 268) on processor 0 due to Breakpoint @ 0xffff8000101486cc [0]kdb> g Entering kdb (current=0xffff0000fa852bc0, pid 268) on processor 0 due to Breakpoint @ 0xffff8000101486cc [0]kdb> ss Entering kdb (current=0xffff0000fa852bc0, pid 268) on processor 0 due to SS trap @ 0xffff800010082ab8 [0]kdb> Fixes: 44679a4f142b ("arm64: KGDB: Add step debugging support") Signed-off-by: Wei Li <liwei391@huawei.com> --- arch/arm64/kernel/kgdb.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)