Hi Lianbo,
On Thu, Sep 19, 2024 at 3:58 PM lijiang <lijiang@xxxxxxxxxx> wrote:
>
> On Thu, Sep 19, 2024 at 11:28 AM Tao Liu <ltao@xxxxxxxxxx> wrote:
>>
>> Hi lianbo,
>>
>> On Thu, Sep 19, 2024 at 2:41 PM lijiang <lijiang@xxxxxxxxxx> wrote:
>> >
>> > Hi, Tao
>> >
>> > Thank you for the fix.
>> >
>> > On Wed, Sep 18, 2024 at 7:44 AM <devel-request@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>> >>
>> >> Date: Wed, 18 Sep 2024 11:42:03 +1200
>> >> From: Tao Liu <ltao@xxxxxxxxxx>
>> >> Subject: [PATCH v1 1/3] ppc64: Fix bt printing error
>> >> stack trace
>> >> To: devel@xxxxxxxxxxxxxxxxxxxxxxxxxxx
>> >> Cc: adityag@xxxxxxxxxxxxx, Tao Liu <ltao@xxxxxxxxxx>
>> >> Message-ID: <20240917234205.7783-2-ltao@xxxxxxxxxx>
>> >> Content-Type: text/plain; charset="US-ASCII"; x-default=true
>> >>
>> >> A error stack trace of bt cmd observed:
>> >>
>> >> crash> bt 1
>> >> PID: 1 TASK: c000000003714b80 CPU: 2 COMMAND: "systemd"
>> >> #0 [c0000000037735c0] _end at c0000000037154b0 (unreliable)
>> >> #1 [c000000003773770] __switch_to at c00000000001fa9c
>> >> #2 [c0000000037737d0] __schedule at c00000000112e4ec
>> >> #3 [c0000000037738b0] schedule at c00000000112ea80
>> >> ...
>> >>
>> >> The #0 stack trace is incorrect, the function address shouldn't exceed _end.
>> >> The reason is for kernel>=v6.2, the offset of pt_regs to sp changed from
>> >> STACK_FRAME_OVERHEAD, i.e 112, to STACK_SWITCH_FRAME_REGS. For
>> >> CONFIG_PPC64_ELF_ABI_V1, it's 112, for ABI_V2, it's 48. So the nip will read a
>> >> wrong value from stack when ABI_V2 enabled.
>> >>
>> >
>> > Can you help to add the related kernel commits to patch log? That will help me a lot to review the patches.
>> >
>> Sure, will update it in v2.
>>
>> >>
>> >> To determine if ABI_V2 enabled is tricky. This patch do it by check the
>> >> following:
>> >
>> >
>> > Can you try to read the value of e_flags from the elf header and to determine what ABI version it is?
>> >
>> Do you mean by checking the following?
>>
>> arch/powerpc/kernel/fadump.c:fadump_init_elfcore_header():
>>
>> if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2))
>> elf->e_flags = 2;
>> else if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V1))
>> elf->e_flags = 1;
>> else
>> elf->e_flags = 0;
>>
>> I think this only works for fadump, but it will not work for normal
>
>
> Maybe "not". I did not try it, but I noticed that there is a similar checking in kernel module, please refer to this one: arch/powerpc/kernel/module_64.c
>
> bool module_elf_check_arch(Elf_Ehdr *hdr)
> {
> unsigned long abi_level = hdr->e_flags & 0x3;
>
> if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2))
> return abi_level == 2;
> else
> return abi_level < 2;
> }
>
>
>> kdump. Also for kcore, the e_flags are set as:
>>
>> read_kcore_iter():
>> #ifndef ELF_CORE_EFLAGS
>> #define ELF_CORE_EFLAGS 0
>> #endif
>> .e_flags = ELF_CORE_EFLAGS,
>>
>> So it seems the e_flags is not a suitable approach for me...
>
>
> The ELF_CORE_EFLAGS should be defined in the arch/powerpc/include/asm/elf.h:
>
> #define ELF_CORE_EFLAGS (is_elf2_task() ? 2 : 0)
>
> And also refer to this one(arch/powerpc/include/asm/thread_info.h):
>
> #if defined(CONFIG_PPC64)
> #define is_elf2_task() (test_thread_flag(TIF_ELF2ABI))
> #else
> #define is_elf2_task() (0)
> #endif
>
> Anyway, can you try it? Or have you already tried it?
Yes you are correct, the ELF_CORE_EFLAGS is not 0. But I tried the
code, checking is_elf2_task(), or test_thread_flag(...) is not as easy
as checking the header of vmlinux. Some processes with thread_flag
0x00, some seem correct, not sure why it occurs, so not a stable
approach to me. See the following:
crash> set -p
crash> task -x
PID: 1208 TASK: c0000000087f9800 CPU: 0 COMMAND: "bash"
struct task_struct {
thread_info = {
...
flags = 0x0
...
crash> set 1
crash> task -x
PID: 1 TASK: c000000003714b80 CPU: 2 COMMAND: "systemd"
struct task_struct {
thread_info = {
...
flags = 0x42000
...
I suggest using the vmlinux header check approach, see the comment in [1].
[1]: https://www.mail-archive.com/devel@xxxxxxxxxxxxxxxxxxxxxxxxxxx/msg01167.html
Thanks,
Tao Liu
>
> Lianbo
>
>>
>> Thanks,
>> Tao Liu
>>
>>
>> > Thanks
>> > Lianbo
>> >
>> >>
>> >>
>> >> In arch/powerpc/include/asm/ppc_asm.h:
>> >> #ifdef CONFIG_PPC64_ELF_ABI_V2
>> >> #define STK_GOT 24
>> >> #else
>> >> #define STK_GOT 40
>> >>
>> >> In arch/powerpc/kernel/tm.S:
>> >> _GLOBAL(tm_reclaim)
>> >> mfcr r5
>> >> mflr r0
>> >> stw r5, 8(r1)
>> >> std r0, 16(r1)
>> >> std r2, STK_GOT(r1)
>> >> ...
>> >>
>> >> So a disassemble on tm_reclaim, and extract the STK_GOT value from std
>> >> instruction is used as the approach.
>> >>
>> >> After the patch:
>> >> crash> bt 1
>> >> PID: 1 TASK: c000000003714b80 CPU: 2 COMMAND: "systemd"
>> >> #0 [c0000000037737d0] __schedule at c00000000112e4ec
>> >> #1 [c0000000037738b0] schedule at c00000000112ea80
>> >> ...
>> >>
>> >> Signed-off-by: Tao Liu <ltao@xxxxxxxxxx>
>> >> ---
>> >> defs.h | 1 +
>> >> ppc64.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---
>> >> 2 files changed, 58 insertions(+), 3 deletions(-)
>> >>
>> >> diff --git a/defs.h b/defs.h
>> >> index 2231cb6..d5cb8cc 100644
>> >> --- a/defs.h
>> >> +++ b/defs.h
>> >> @@ -4643,6 +4643,7 @@ struct efi_memory_desc_t {
>> >> #define MSR_PR_LG 14 /* Problem State / Privilege Level */
>> >> /* Used to find the user or kernel-mode frame*/
>> >>
>> >> +#define STACK_SWITCH_FRAME_REGS 48
>> >> #define STACK_FRAME_OVERHEAD 112
>> >> #define EXCP_FRAME_MARKER 0x7265677368657265
>> >>
>> >> diff --git a/ppc64.c b/ppc64.c
>> >> index e8930a1..6e5f155 100644
>> >> --- a/ppc64.c
>> >> +++ b/ppc64.c
>> >> @@ -72,6 +72,7 @@ static ulong pud_page_vaddr_l4(ulong pud);
>> >> static ulong pmd_page_vaddr_l4(ulong pmd);
>> >> static int is_opal_context(ulong sp, ulong nip);
>> >> void opalmsg(void);
>> >> +static bool is_ppc64_elf_abi_v2(void);
>> >>
>> >> static int is_opal_context(ulong sp, ulong nip)
>> >> {
>> >> @@ -2813,6 +2814,51 @@ ppc64_get_sp(ulong task)
>> >> return sp;
>> >> }
>> >>
>> >> +static bool
>> >> +is_ppc64_elf_abi_v2(void)
>> >> +{
>> >> + char buf1[BUFSIZE];
>> >> + char *pos1, *pos2;
>> >> + int errflag = 0;
>> >> + ulong stk_got = 0;
>> >> + static bool ret = false;
>> >> + static bool checked = false;
>> >> +
>> >> + if (checked == true || !symbol_exists("tm_reclaim"))
>> >> + return ret;
>> >> +
>> >> + sprintf(buf1, "x/16i tm_reclaim");
>> >> + open_tmpfile();
>> >> + if (!gdb_pass_through(buf1, pc->tmpfile, GNU_RETURN_ON_ERROR))
>> >> + goto out;
>> >> + checked = true;
>> >> + rewind(pc->tmpfile);
>> >> + while (fgets(buf1, BUFSIZE, pc->tmpfile)) {
>> >> + // "std r2, STK_GOT(r1)" is expected
>> >> + if (strstr(buf1, "std") &&
>> >> + strstr(buf1, "(r1)") &&
>> >> + (pos1 = strstr(buf1, "r2,"))) {
>> >> + pos1 += strlen("r2,");
>> >> + for (pos2 = pos1; *pos2 != '\0' && *pos2 != '('; pos2++);
>> >> + *pos2 = '\0';
>> >> + stk_got = stol(pos1, RETURN_ON_ERROR|QUIET, &errflag);
>> >> + break;
>> >> + }
>> >> + }
>> >> +
>> >> + if (!errflag) {
>> >> + switch (stk_got) {
>> >> + case 24:
>> >> + ret = true;
>> >> + case 40:
>> >> + goto out;
>> >> + }
>> >> + }
>> >> + error(WARNING, "Unstable elf_abi v1/v2 detection.\n");
>> >> +out:
>> >> + close_tmpfile();
>> >> + return ret;
>> >> +}
>> >>
>> >> /*
>> >> * get the SP and PC values for idle tasks.
>> >> @@ -2834,9 +2880,17 @@ get_ppc64_frame(struct bt_info *bt, ulong *getpc, ulong *getsp)
>> >> sp = ppc64_get_sp(task);
>> >> if (!INSTACK(sp, bt))
>> >> goto out;
>> >> - readmem(sp+STACK_FRAME_OVERHEAD, KVADDR, ®s,
>> >> - sizeof(struct ppc64_pt_regs),
>> >> - "PPC64 pt_regs", FAULT_ON_ERROR);
>> >> +
>> >> + if (THIS_KERNEL_VERSION >= LINUX(6,2,0) && is_ppc64_elf_abi_v2()) {
>> >> + readmem(sp+STACK_SWITCH_FRAME_REGS, KVADDR, ®s,
>> >> + sizeof(struct ppc64_pt_regs),
>> >> + "PPC64 pt_regs", FAULT_ON_ERROR);
>> >> + } else {
>> >> + readmem(sp+STACK_FRAME_OVERHEAD, KVADDR, ®s,
>> >> + sizeof(struct ppc64_pt_regs),
>> >> + "PPC64 pt_regs", FAULT_ON_ERROR);
>> >> + }
>> >> +
>> >> ip = regs.nip;
>> >> closest = closest_symbol(ip);
>> >> if (STREQ(closest, ".__switch_to") || STREQ(closest, "__switch_to")) {
>> >> --
>> >> 2.40.1
>>
--
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