Hi Tao,
On 04/10/24 10:40, Tao Lou wrote:
Hi Aditya & lianbo,
On Tue, Sep 24, 2024 at 2:28 AM Aditya Gupta <adityag@xxxxxxxxxxxxx> wrote:
Hi Tao,
On 24/09/22 10:25PM, Aditya Gupta wrote:
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@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)
+{
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).
How about this approach ?
I feel this might be more dependable, as the file command also uses
this, as well as fadump (PowerPC firmware-assisted dump) in the kernel.
As a sidenote, there is still some issue either in patch #1 or #3
causing all secondary CPUs (where swapper task is running) to show all
threads as '_end'
What do you think ?
I think your approach will work, thanks for your code! Please see my
comments inlined in the code:
Either way what you chose, I do realise the idea to utilise the
'std r2, STK_GOT(r1)' in such a way, was interesting and smart.
static bool
is_ppc64_elf_abi_v2(void)
{
const char *kernel_file = pc->namelist;
int fd, swap;
char eheader[BUFSIZE];
Elf64_Ehdr *elf64;
if ((fd = open(kernel_file, O_RDONLY)) < 0) {
error(INFO, "%s: %s\n", kernel_file, strerror(errno));
return FALSE;
}
if (read(fd, eheader, BUFSIZE) != BUFSIZE) {
error(INFO, "%s: %s\n", kernel_file, strerror(errno));
close(fd);
return FALSE;
}
close(fd);
if (!STRNEQ(eheader, ELFMAG) || eheader[EI_VERSION] != EV_CURRENT)
return FALSE;
elf64 = (Elf64_Ehdr *)&eheader[0];
swap = (((eheader[EI_DATA] == ELFDATA2LSB) &&
(__BYTE_ORDER == __BIG_ENDIAN)) ||
((eheader[EI_DATA] == ELFDATA2MSB) &&
(__BYTE_ORDER == __LITTLE_ENDIAN)));
The above code seems duplicated with the one in is_kernel(), in fact,
is_kernel() will be invoked at the very beginning to determine if one
file is vmlinux, so I would suggest to add our abi_v2 check here,
like:
in ppc64.c:
int ppc64_elf_abi = 0;
static bool is_ppc64_elf_abi_v2(void)
{
if (ppc64_elf_abi == 1)
...
else if (ppc64_elf_abi == 2)
...
else
...
}
in symbols.c:is_kernel():
...
} else if ((elf64->e_ident[EI_CLASS] == ELFCLASS64) &&
((swap16(elf64->e_type, swap) == ET_EXEC) ||
...
case EM_PPC64:
if (machine_type_mismatch(file, "PPC64", NULL, 0))
goto bailout;
+ else
+ ppc64_elf_abi = swap32(elf64->e_flags, swap);
break;
So we can initial the abi version at crash start only once, and get
rid of the code duplication.
Yes, I actually copied pasted the initial part from is_kernel.
The approach is good, just to clarify, we know that is_kernel will be
called everytime before this check right ?
Thanks,
Aditya Gupta
/*
* The ABI version is stored in E_FLAGS in the ELF header, atleast for
* ppc64 binaries.
*
* These logic is also used by the 'file' command, which states this in
* its magic file:
*
* >18 leshort 20 PowerPC or cisco 4500,
* >18 leshort 21 64-bit PowerPC or cisco 7500,
* >>48 lelong 0 Unspecified or Power ELF V1 ABI,
* >>48 lelong 1 Power ELF V1 ABI,
* >>48 lelong 2 OpenPOWER ELF V2 ABI,
*
* The '>18' above means, data at 18 (0x12), which is basically
* 'elf64->e_machine', which will be 20 for PPC, and 21 for PPC64
*
* Similarly, '>>48' is offset 48 (0x30) in the file, which is
* basically 'elf64->e_flags', which has the ELF ABI version
*/
if (elf64->e_flags == 2) {
/* ABI v2 */
return TRUE;
} else if (elf64->e_flags == 1) {
/* ABI v1 */
return FALSE;
}
error(WARNING, "Unstable elf_abi v1/v2 detection.\n");
return FALSE;
}
Also, we can those values in the ELF header:
$ hexdump vmlinux-little-endian
0000000 457f 464c 0102 0001 0000 0000 0000 0000
0000010 0002 0015 (= 21 = E_MACHINE) 0001 0000 0000 0000 0000 c000
0000020 0040 0000 0000 0000 8bf8 0040 0000 0000
0000030 0002 (= E_FLAGS = ABI) 0000 0040 0038 0002 0040 0027 0026
0000040 0001 0000 0007 0000 0000 0001 0000 0000
I agree with the elf header check on the vmlinux file, it is much
simpler. Also I compiled the kernel with CONFIG_PPC64_ELF_ABI_V1 on,
the file cmd will give: Power ELF V1 ABI string. So the approach can
work.
Also, I see 'pc->namelist' is basically the kernel filename, is that
correct ? Can that be renamed to kernel_filename or something ?
Yes, by reading through the code, pc->namelist is vmlinux, and
pc->namelist_debug is the debug symbol if vmlinux doesn't have the
symbol. But I didn't see the need for the rename.
Thanks,
Tao Liu
Thanks,
Aditya Gupta
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")) {
--
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