[Crash-utility] [PATCH] ppc64: Fix bt printing error stack trace

[Tao Liu <ltao@xxxxxxxxxx>]

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.

To determine if ABI_V2 enabled is tricky. This patch do it by check the
following:

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>
---

This patch is the follow-up of gdb stack unwinding support v7 discussion[1],
where a "gdb bt" fail is observed. After applying the patch, the "gdb bt" can
also work normal for gdb stack unwinding support v7.

[1]: https://www.mail-archive.com/devel@xxxxxxxxxxxxxxxxxxxxxxxxxxx/msg01120.html

---
 defs.h  |  1 +
 ppc64.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 57 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..5e2595e 100644
--- a/ppc64.c
+++ b/ppc64.c
@@ -2813,6 +2813,51 @@ 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 +2879,17 @@ 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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