11:55 a.m.
Hi Tao,
On 18/09/24 05:12, Tao Liu wrote:
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(a)redhat.com>
---
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)
+{
Thanks for fixing these issues on ppc64 !
It is good. I am also checking if there is a way to implement
'is_ppc64_elf_abi_v2' by getting ABI version from the ELF notes, as
'file' command somehow does know:
$ file vmlinux-little-endian vmlinux-little-endian: ELF 64-bit LSB
executable, 64-bit PowerPC or cisco 7500, OpenPOWER ELF V2 ABI, version
1 (SYSV), statically linked,
BuildID[sha1]=f6449970e6af6cddeed1e260393e2377ccc0f369, not stripped
That might be more dependable (if we can do that).
Thanks,
Aditya Gupta
> + 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")) {