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 ?
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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