Hi Aditya,
On Tue, Oct 8, 2024 at 10:18 PM Aditya Gupta <adityag@xxxxxxxxxxxxx> wrote:
>
> 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 ?
Actually I used another approach rather than is_kernel(), see [1] for
v2 patchset of ppc64 fixing.
The reason is keeping a ppc64 specific variable in the multi-cpu arch
used function is_kernel(), it is hard to make the code as clean.
[1]: https://www.mail-archive.com/devel@xxxxxxxxxxxxxxxxxxxxxxxxxxx/msg01170.html
Thanks,
Tao Liu
>
>
> 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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