Re: [PATCH 6/6] LoongArch: Add generic ex-handler unwind in prologue unwinder

From: Qing Zhang
Date: Thu Dec 15 2022 - 07:05:05 EST

Hi, Jinyang

On 2022/12/15 下午12:01, Jinyang He wrote:
When exception is triggered, code flow go handle_\exception in some
cases. One of stackframe in this case as follows,

high -> +-------+
| REGS | <- a pt_regs
| |
| | <- ex trigger
| REGS | <- ex pt_regs <-+
| | |
| | |
low -> +-------+ ->unwind-+

When unwinder unwind to handler_\exception it cannot go on prologue
analysis. It is asynchronous code flow, we should get the next frame
PC from regs->csr_era but not from regs->regs[1]. And we copy the
handler codes to eentry in the early time and copy the handler codes
to NUMA-relative memory named pcpu_handlers if NUMA is enabled. Thus,
unwinder cannot unwind normally. Therefore, try to give some hint in
handler_\exception and fixup it in unwind_next_frame.

Reported-by: Qing Zhang <zhangqing@xxxxxxxxxxx>
Signed-off-by: Jinyang He <hejinyang@xxxxxxxxxxx>
---
arch/loongarch/include/asm/unwind.h | 2 +-
arch/loongarch/kernel/genex.S | 3 +
arch/loongarch/kernel/unwind_prologue.c | 100 +++++++++++++++++++++---
arch/loongarch/mm/tlb.c | 2 +-
4 files changed, 92 insertions(+), 15 deletions(-)

The others look good to me, but there is still a small problem:
When I tested hw_breakpoint.ko with prologue unwinder,
sometimes output address [<9000000100302724>] 0x9000000100302724, eg: CPU: 3 PID: 0
But some processes are normal, eg: CPU: 0 PID: 0

[27.655549] CPU: 3 PID: 0 Comm: swapper/3 Not tainted 6.1.0-rc8 #9
[27.655552] Hardware name: Loongson Loongson-3A5000-7A1000-1w-A2101/
Loongson-LS3A5000-7A1000-1w-A2101, BIOS vUDK2018-LoongArch-V2.0.pre-beta8 06/15/2022

[27.655604]...
[27.655606] Call Trace:
[27.655607] [<9000000000222f88>] show_stack+0x60/0x184
[27.655613] [<90000000010e9b8c>] dump_stack_lvl+0x60/0x88
[27.655618] [] sample_hbp_handler+0x30/0x4c [data_breakpoint]
[27.655626] [<900000000037c8a0>] __perf_event_overflow+0x84/0x26c
[27.655629] [<900000000038980c>] perf_bp_event+0xc0/0xc8
[27.655633] [<900000000022e3bc>] watchpoint_handler+0x54/0x88
[27.655637] [<90000000010ea2f8>] do_watch+0x30/0x48
[27.655640] [<9000000100302724>] 0x9000000100302724 // Not natural
[27.655642] [<9000000000ab4cbc>] add_interrupt_randomness+0x60/0xbc
[27.655646] [<90000000002a0fa0>] handle_irq_event_percpu+0x28/0x70
[27.655650] [<90000000002a6f9c>] handle_percpu_irq+0x54/0x88
[27.655652] [<90000000002a025c>] generic_handle_domain_irq+0x28/0x40
[27.655655] [<9000000000995458>] handle_cpu_irq+0x68/0xa4
[27.655658] [<90000000010ea8dc>] handle_loongarch_irq+0x34/0x4c
[27.655661] [<90000000010ea974>] do_vint+0x80/0xb4
[27.655664] [<90000000002216a0>] __arch_cpu_idle+0x20/0x24
[27.655667] [<90000000010f8178>] default_idle_call+0x30/0x58
[27.655670] [<90000000002825cc>] do_idle+0xb4/0x118
[27.655674] [<900000000028281c>] cpu_startup_entry+0x20/0x24
[27.655677] [<900000000022b198>] start_secondary+0x9c/0xa4
[27.655679] [<90000000010eb124>] smpboot_entry+0x60/0x64


[27.658940] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.1.0-rc8 #9
...
[28.229978] Call Trace:
[28.229979] [<9000000000222f88>] show_stack+0x60/0x184
[28.237503] [<90000000010e9b8c>] dump_stack_lvl+0x60/0x88
[28.242866] [] sample_hbp_handler+0x30/0x4c [data_breakpoint]
[28.250132] [<900000000037c8a0>] __perf_event_overflow+0x84/0x26c
[28.256186] [<900000000038980c>] perf_bp_event+0xc0/0xc8
[28.261462] [<900000000022e3bc>] watchpoint_handler+0x54/0x88
[28.267170] [<90000000010ea2f8>] do_watch+0x30/0x48
[28.272013] [<90000000017d2724>] exception_handlers+0x2724/0x1000 //...
[28.278155] [<9000000000ab4cbc>] add_interrupt_randomness+0x60/0xbc
[28.284381] [<90000000002a0fa0>] handle_irq_event_percpu+0x28/0x70
[28.290520] [<90000000002a6f9c>] handle_percpu_irq+0x54/0x88
[28.296140] [<90000000002a025c>] generic_handle_domain_irq+0x28/0x40
[28.302452] [<9000000000995458>] handle_cpu_irq+0x68/0xa4
[28.307813] [<90000000010ea8dc>] handle_loongarch_irq+0x34/0x4c
[28.313693] [<90000000010ea974>] do_vint+0x80/0xb4
[28.318450] [<90000000002216a0>] __arch_cpu_idle+0x20/0x24
[28.323897] [<90000000010f8178>] default_idle_call+0x30/0x58
[28.329518] [<90000000002825cc>] do_idle+0xb4/0x118
[28.334361] [<900000000028281c>] cpu_startup_entry+0x20/0x24
[28.339982] [<90000000010ec0dc>] kernel_init+0x0/0x110
[28.345085] [<90000000011106f8>] arch_post_acpi_subsys_init+0x0/0x4

Maybe sometimes assembly kallsyms is not recognized, let me think...

Thanks,
-Qing

diff --git a/arch/loongarch/include/asm/unwind.h b/arch/loongarch/include/asm/unwind.h
index a16aff1d086a..c02cb3b39fe2 100644
--- a/arch/loongarch/include/asm/unwind.h
+++ b/arch/loongarch/include/asm/unwind.h
@@ -24,7 +24,7 @@ struct unwind_state {
char type; /* UNWINDER_XXX */
struct stack_info stack_info;
struct task_struct *task;
- bool first, error, is_ftrace;
+ bool first, error, reset;
int graph_idx;
unsigned long sp, pc, ra;
const struct unwinder_ops *ops;
diff --git a/arch/loongarch/kernel/genex.S b/arch/loongarch/kernel/genex.S
index 75e5be807a0d..7e5c293ed89f 100644
--- a/arch/loongarch/kernel/genex.S
+++ b/arch/loongarch/kernel/genex.S
@@ -67,14 +67,17 @@ SYM_FUNC_END(except_vec_cex)
.macro BUILD_HANDLER exception handler prep
.align 5
SYM_FUNC_START(handle_\exception)
+ 666:
BACKUP_T0T1
SAVE_ALL
build_prep_\prep
move a0, sp
la.abs t0, do_\handler
jirl ra, t0, 0
+ 668:
RESTORE_ALL_AND_RET
SYM_FUNC_END(handle_\exception)
+ SYM_DATA(unwind_hint_\exception, .word 668b - 666b)
.endm
BUILD_HANDLER ade ade badv
diff --git a/arch/loongarch/kernel/unwind_prologue.c b/arch/loongarch/kernel/unwind_prologue.c
index 441641227c10..c34bb035ac56 100644
--- a/arch/loongarch/kernel/unwind_prologue.c
+++ b/arch/loongarch/kernel/unwind_prologue.c
@@ -2,23 +2,102 @@
/*
* Copyright (C) 2022 Loongson Technology Corporation Limited
*/
+#include <linux/cpumask.h>
#include <linux/ftrace.h>
#include <linux/kallsyms.h>
#include <asm/inst.h>
+#include <asm/loongson.h>
#include <asm/ptrace.h>
+#include <asm/setup.h>
#include <asm/unwind.h>
static const struct unwinder_ops *guard_unwinder = &unwinder_guess;
-static inline void unwind_state_fixup(struct unwind_state *state)
+extern const int unwind_hint_ade;
+extern const int unwind_hint_ale;
+extern const int unwind_hint_bp;
+extern const int unwind_hint_fpe;
+extern const int unwind_hint_fpu;
+extern const int unwind_hint_lsx;
+extern const int unwind_hint_lasx;
+extern const int unwind_hint_lbt;
+extern const int unwind_hint_ri;
+extern const int unwind_hint_watch;
+extern unsigned long eentry;
+#ifdef CONFIG_NUMA
+extern unsigned long pcpu_handlers[NR_CPUS];
+#endif
+
+static inline bool scan_handler(unsigned long entry_offset)
{
-#ifdef CONFIG_DYNAMIC_FTRACE
- static unsigned long ftrace = (unsigned long)ftrace_call + 4;
+ int idx, offset;
- if (state->pc == ftrace)
- state->is_ftrace = true;
+ if (entry_offset >= EXCCODE_INT_START * VECSIZE)
+ return false;
+
+ idx = entry_offset / VECSIZE;
+ offset = entry_offset % VECSIZE;
+ switch (idx) {
+ case EXCCODE_ADE:
+ return offset == unwind_hint_ade;
+ case EXCCODE_ALE:
+ return offset == unwind_hint_ale;
+ case EXCCODE_BP:
+ return offset == unwind_hint_bp;
+ case EXCCODE_FPE:
+ return offset == unwind_hint_fpe;
+ case EXCCODE_FPDIS:
+ return offset == unwind_hint_fpu;
+ case EXCCODE_LSXDIS:
+ return offset == unwind_hint_lsx;
+ case EXCCODE_LASXDIS:
+ return offset == unwind_hint_lasx;
+ case EXCCODE_BTDIS:
+ return offset == unwind_hint_lbt;
+ case EXCCODE_INE:
+ return offset == unwind_hint_ri;
+ case EXCCODE_WATCH:
+ return offset == unwind_hint_watch;
+ default:
+ return false;
+ }
+}
+
+static inline bool fix_exceptions(unsigned long pc)
+{
+#ifdef CONFIG_NUMA
+ int cpu;
+
+ for_each_possible_cpu(cpu) {
+ if (!pcpu_handlers[cpu])
+ continue;
+ if (scan_handler(pc - pcpu_handlers[cpu]))
+ return true;
+ }
#endif
+ return scan_handler(pc - eentry);
+}
+
+/*
+ * As we meet ftrace_regs_entry, reset first flag like first doing
+ * tracing. Prologue analysis will stop soon because PC is at entry.
+ */
+static inline bool fix_ftrace(unsigned long pc)
+{
+#ifdef CONFIG_DYNAMIC_FTRACE
+ return pc == (unsigned long)ftrace_call + LOONGARCH_INSN_SIZE;
+#else
+ return false;
+#endif
+}
+
+static inline bool unwind_state_fixup(struct unwind_state *state)
+{
+ if (!fix_exceptions(state->pc) && !fix_ftrace(state->pc))
+ return false;
+ state->reset = true;
+ return true;
}
static unsigned long get_return_address(struct unwind_state *state)
@@ -46,14 +125,10 @@ static bool unwind_by_prologue(struct unwind_state *state)
if (state->sp >= info->end || state->sp < info->begin)
return false;
- if (state->is_ftrace) {
- /*
- * As we meet ftrace_regs_entry, reset first flag like first doing
- * tracing. Prologue analysis will stop soon because PC is at entry.
- */
+ if (state->reset) {
regs = (struct pt_regs *)state->sp;
state->first = true;
- state->is_ftrace = false;
+ state->reset = false;
state->pc = regs->csr_era;
state->ra = regs->regs[1];
state->sp = regs->regs[3];
@@ -118,8 +193,7 @@ static bool unwind_by_prologue(struct unwind_state *state)
out:
state->first = false;
- unwind_state_fixup(state);
- return !!__kernel_text_address(state->pc);
+ return unwind_state_fixup(state) || __kernel_text_address(state->pc);
}
static int raw_show_trace;
diff --git a/arch/loongarch/mm/tlb.c b/arch/loongarch/mm/tlb.c
index da3681f131c8..8bad6b0cff59 100644
--- a/arch/loongarch/mm/tlb.c
+++ b/arch/loongarch/mm/tlb.c
@@ -251,7 +251,7 @@ static void output_pgtable_bits_defines(void)
}
#ifdef CONFIG_NUMA
-static unsigned long pcpu_handlers[NR_CPUS];
+unsigned long pcpu_handlers[NR_CPUS];
#endif
extern long exception_handlers[VECSIZE * 128 / sizeof(long)];