[Crash-utility] Re: [PATCH v1 1/3] ppc64: Fix bt printing error stack trace

[lijiang <lijiang@xxxxxxxxxx>]

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.

 

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?

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, &regs,
-               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, &regs,
+                       sizeof(struct ppc64_pt_regs),
+                       "PPC64 pt_regs", FAULT_ON_ERROR);
+       } else {
+               readmem(sp+STACK_FRAME_OVERHEAD, KVADDR, &regs,
+                       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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