Hi Aditya & Lianbo,
Thanks for your review on this ppc fix. Recently I'm working on
another high priority task, so I may not respond to your comments in
time, sorry for that.
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 ?
Yes, I like the idea of extracting the abi version through vmlinux.
Thanks a lot for your approach and code, but I haven't tried your code
yet. I will test it when my current task finishes.
Thanks,
Tao Liu
>
> 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 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
>
> Also, I see 'pc->namelist' is basically the kernel filename, is that
> correct ? Can that be renamed to kernel_filename or something ?
>
> 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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