Hi Lianbo,
On Mon, Dec 18, 2023 at 07:43:27PM +0800, Lianbo Jiang wrote:
> Thank you for the update, Aditya.
>
> On 12/15/23 15:59, Aditya Gupta wrote:
> > Currently, gdb passthroughs of 'bt', 'frame', 'up', 'down', 'info
> > locals' don't work. This is due to gdb not knowing the register values to
> > unwind the stack frames
> >
> > Every gdb passthrough goes through `gdb_interface`. And then, gdb expects
> > `crash_target::fetch_registers` to give it the register values, which is
> > dependent on `machdep->get_cpu_reg` to read the register values for
> > specific architecture.
> >
> > ┌────────────────────────┐
> > gdb passthrough (eg. "bt") │ │
> > crash ─────────────────────────▶│ │
> > │ gdb_interface │
> > │ │
> > │ │
> > │ ┌────────────────────┐ │
> > fetch_registers │ │ │ │
> > crash_target◀────────────────────────┼─┤ gdb │ │
> > ─────────────────────────┼▶│ │ │
> > Registers (SP,NIP, etc.)│ │ │ │
> > │ │ │ │
> > │ └────────────────────┘ │
> > └────────────────────────┘
> >
> > Implement `machdep->get_cpu_reg` on PPC64, so that crash provides the
> > register values to gdb to unwind stack frames properly
> >
> > With these changes, on powerpc, 'bt' command output in gdb mode, will look
> > like this:
> >
> > gdb> bt
> > #0 0xc0000000002a53e8 in crash_setup_regs (oldregs=<optimized out>,
> > newregs=0xc00000000486f8d8) at ./arch/powerpc/include/asm/kexec.h:69
> > #1 __crash_kexec (regs=<optimized out>) at kernel/kexec_core.c:974
> > #2 0xc000000000168918 in panic (fmt=<optimized out>) at
> > kernel/panic.c:358
> > #3 0xc000000000b735f8 in sysrq_handle_crash (key=<optimized out>) at
> > drivers/tty/sysrq.c:155
> > #4 0xc000000000b742cc in __handle_sysrq (key=key@entry=99,
> > check_mask=check_mask@entry=false) at drivers/tty/sysrq.c:602
> > #5 0xc000000000b7506c in write_sysrq_trigger (file=<optimized out>,
> > buf=<optimized out>, count=2, ppos=<optimized out>) at
> > drivers/tty/sysrq.c:1163
> > #6 0xc00000000069a7bc in pde_write (ppos=<optimized out>,
> > count=<optimized out>, buf=<optimized out>, file=<optimized out>,
> > pde=0xc000000009ed3a80) at fs/proc/inode.c:340
> > #7 proc_reg_write (file=<optimized out>, buf=<optimized out>,
> > count=<optimized out>, ppos=<optimized out>) at fs/proc/inode.c:352
> > #8 0xc0000000005b3bbc in vfs_write
> > (file=file@entry=0xc00000009dda7d00, buf=buf@entry=0xebcfc7c6040 <error:
> > Cannot access memory at address 0xebcfc7c6040>, count=count@entry=2,
> > pos=pos@entry=0xc00000000486fda0) at fs/read_write.c:582
> >
> > instead of earlier output without this patch:
> >
> > gdb> bt
> > #0 <unavailable> in ?? ()
> > Backtrace stopped: previous frame identical to this frame (corrupt
> > stack?)
> >
> > Also, 'get_dumpfile_regs' has been introduced to get registers from
> > multiple supported vmcore formats. Correspondingly a flag 'BT_NO_PRINT_REGS'
> > has been introduced to tell helper functions to get registers, to not
> > print registers with every call to backtrace in gdb.
> >
> > Note: This feature to support GDB unwinding doesn't support live debugging
> >
> > Signed-off-by: Aditya Gupta <[email protected]>
> > ---
> > defs.h | 124 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > kernel.c | 33 +++++++++++++++
> > ppc64.c | 108 ++++++++++++++++++++++++++++++++++++++++++++++--
> > 3 files changed, 262 insertions(+), 3 deletions(-)
> >
> > diff --git a/defs.h b/defs.h
> > index 5218a94fe4a4..0c80de72e89e 100644
> > --- a/defs.h
> > +++ b/defs.h
> > @@ -6023,6 +6023,7 @@ int load_module_symbols_helper(char *);
> > void unlink_module(struct load_module *);
> > int check_specified_module_tree(char *, char *);
> > int is_system_call(char *, ulong);
> > +void get_dumpfile_regs(struct bt_info*, ulong*, ulong*);
> > void generic_dump_irq(int);
> > void generic_get_irq_affinity(int);
> > void generic_show_interrupts(int, ulong *);
> > @@ -6121,6 +6122,7 @@ ulong cpu_map_addr(const char *type);
> > #define BT_REGS_NOT_FOUND (0x4000000000000ULL)
> > #define BT_OVERFLOW_STACK (0x8000000000000ULL)
> > #define BT_SKIP_IDLE (0x10000000000000ULL)
> > +#define BT_NO_PRINT_REGS (0x20000000000000ULL)
> > #define BT_SYMBOL_OFFSET (BT_SYMBOLIC_ARGS)
> > #define BT_REF_HEXVAL (0x1)
> > @@ -6662,6 +6664,8 @@ struct machine_specific {
> > void ppc64_init(int);
> > void ppc64_dump_machdep_table(ulong);
> > +int ppc64_get_cpu_reg(int cpu, int regno, const char *name, int size,
> > + void *value);
>
> This is only invoked in ppc64 module, so it should be good to define this
> function in the ppc64.c, and use the keywork 'static'.
>
> Given that, no need to add it in defs.h.
Sure, I will make it static, and remove it from defs.h.
>
> > #define display_idt_table() \
> > error(FATAL, "-d option is not applicable to PowerPC
> > architecture\n")
> > #define KSYMS_START (0x1)
> > @@ -7854,4 +7858,124 @@ enum x86_64_regnum {
> > LAST_REGNUM
> > };
> > +/*
> > + * Register numbers to make crash_target->fetch_registers()
> > + * ---> machdep->get_cpu_reg() work properly.
> > + *
> > + * These register numbers and names are given according to output of
> > + * `rs6000_register_name`, because that is what was being used by
> > + * crash_target::fetch_registers in case of PPC64
> > + */
>
> Some register number constants are defined in the gdb/ppc-tdep.h:
>
> enum {
> PPC_R0_REGNUM = 0,
> PPC_F0_REGNUM = 32,
> PPC_PC_REGNUM = 64,
> ...
Thanks for the reference.
>
> }
>
> Do you mean that other undefined registers won't be used in this case? Just
> a confirmation.
Yes, other registers won't be handled, since they are not in the stack frame
according to the ABI at
https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi.html#STACK
In 'ppc64_get_cpu_reg' we simply return from the function for any undefined
register number.
>
> > +enum ppc64_renum {
> > + PPC64_R0_REGNUM = 0,
> > + PPC64_R1_REGNUM,
> > + PPC64_R2_REGNUM,
> > + PPC64_R3_REGNUM,
> > + PPC64_R4_REGNUM,
> > + PPC64_R5_REGNUM,
> > + PPC64_R6_REGNUM,
> > + PPC64_R7_REGNUM,
> > + PPC64_R8_REGNUM,
> > + PPC64_R9_REGNUM,
> > + PPC64_R10_REGNUM,
> > + PPC64_R11_REGNUM,
> > + PPC64_R12_REGNUM,
> > + PPC64_R13_REGNUM,
> > + PPC64_R14_REGNUM,
> > + PPC64_R15_REGNUM,
> > + PPC64_R16_REGNUM,
> > + PPC64_R17_REGNUM,
> > + PPC64_R18_REGNUM,
> > + PPC64_R19_REGNUM,
> > + PPC64_R20_REGNUM,
> > + PPC64_R21_REGNUM,
> > + PPC64_R22_REGNUM,
> > + PPC64_R23_REGNUM,
> > + PPC64_R24_REGNUM,
> > + PPC64_R25_REGNUM,
> > + PPC64_R26_REGNUM,
> > + PPC64_R27_REGNUM,
> > + PPC64_R28_REGNUM,
> > + PPC64_R29_REGNUM,
> > + PPC64_R30_REGNUM,
> > + PPC64_R31_REGNUM,
> > +
> > + PPC64_F0_REGNUM = 32,
> > + PPC64_F1_REGNUM,
> > + PPC64_F2_REGNUM,
> > + PPC64_F3_REGNUM,
> > + PPC64_F4_REGNUM,
> > + PPC64_F5_REGNUM,
> > + PPC64_F6_REGNUM,
> > + PPC64_F7_REGNUM,
> > + PPC64_F8_REGNUM,
> > + PPC64_F9_REGNUM,
> > + PPC64_F10_REGNUM,
> > + PPC64_F11_REGNUM,
> > + PPC64_F12_REGNUM,
> > + PPC64_F13_REGNUM,
> > + PPC64_F14_REGNUM,
> > + PPC64_F15_REGNUM,
> > + PPC64_F16_REGNUM,
> > + PPC64_F17_REGNUM,
> > + PPC64_F18_REGNUM,
> > + PPC64_F19_REGNUM,
> > + PPC64_F20_REGNUM,
> > + PPC64_F21_REGNUM,
> > + PPC64_F22_REGNUM,
> > + PPC64_F23_REGNUM,
> > + PPC64_F24_REGNUM,
> > + PPC64_F25_REGNUM,
> > + PPC64_F26_REGNUM,
> > + PPC64_F27_REGNUM,
> > + PPC64_F28_REGNUM,
> > + PPC64_F29_REGNUM,
> > + PPC64_F30_REGNUM,
> > + PPC64_F31_REGNUM,
> > +
> > + PPC64_PC_REGNUM = 64,
> > + PPC64_MSR_REGNUM = 65,
> > + PPC64_CR_REGNUM = 66,
> > + PPC64_LR_REGNUM = 67,
> > + PPC64_CTR_REGNUM = 68,
> > + PPC64_XER_REGNUM = 69,
> > + PPC64_FPSCR_REGNUM = 70,
> > +
> > + PPC64_VR0_REGNUM = 106,
> > + PPC64_VR1_REGNUM,
> > + PPC64_VR2_REGNUM,
> > + PPC64_VR3_REGNUM,
> > + PPC64_VR4_REGNUM,
> > + PPC64_VR5_REGNUM,
> > + PPC64_VR6_REGNUM,
> > + PPC64_VR7_REGNUM,
> > + PPC64_VR8_REGNUM,
> > + PPC64_VR9_REGNUM,
> > + PPC64_VR10_REGNUM,
> > + PPC64_VR11_REGNUM,
> > + PPC64_VR12_REGNUM,
> > + PPC64_VR13_REGNUM,
> > + PPC64_VR14_REGNUM,
> > + PPC64_VR15_REGNUM,
> > + PPC64_VR16_REGNUM,
> > + PPC64_VR17_REGNUM,
> > + PPC64_VR18_REGNUM,
> > + PPC64_VR19_REGNUM,
> > + PPC64_VR20_REGNUM,
> > + PPC64_VR21_REGNUM,
> > + PPC64_VR22_REGNUM,
> > + PPC64_VR23_REGNUM,
> > + PPC64_VR24_REGNUM,
> > + PPC64_VR25_REGNUM,
> > + PPC64_VR26_REGNUM,
> > + PPC64_VR27_REGNUM,
> > + PPC64_VR28_REGNUM,
> > + PPC64_VR29_REGNUM,
> > + PPC64_VR30_REGNUM,
> > + PPC64_VR31_REGNUM,
> > +
> > + PPC64_VSCR_REGNUM = 138,
> > + PPC64_VRSAVE_REGNU = 139
> > +};
> > +
> > #endif /* !GDB_COMMON */
> > diff --git a/kernel.c b/kernel.c
> > index 6dcf414693e6..52b7ba09f390 100644
> > --- a/kernel.c
> > +++ b/kernel.c
> > @@ -3533,6 +3533,39 @@ get_lkcd_regs(struct bt_info *bt, ulong *eip, ulong
> > *esp)
> > machdep->get_stack_frame(bt, eip, esp);
> > }
> > +void
> > +get_dumpfile_regs(struct bt_info *bt, ulong *eip, ulong *esp)
> > +{
> > + bt->flags |= BT_NO_PRINT_REGS;
> > +
> > + if (NETDUMP_DUMPFILE())
> > + get_netdump_regs(bt, eip, esp);
> > + else if (KDUMP_DUMPFILE())
> > + get_kdump_regs(bt, eip, esp);
> > + else if (DISKDUMP_DUMPFILE())
> > + get_diskdump_regs(bt, eip, esp);
> > + else if (KVMDUMP_DUMPFILE())
> > + get_kvmdump_regs(bt, eip, esp);
> > + else if (LKCD_DUMPFILE())
> > + get_lkcd_regs(bt, eip, esp);
> > + else if (XENDUMP_DUMPFILE())
> > + get_xendump_regs(bt, eip, esp);
> > + else if (SADUMP_DUMPFILE())
> > + get_sadump_regs(bt, eip, esp);
> > + else if (VMSS_DUMPFILE())
> > + get_vmware_vmss_regs(bt, eip, esp);
> > + else if (REMOTE_PAUSED()) {
> > + if (!is_task_active(bt->task) || !get_remote_regs(bt, eip, esp))
> > + machdep->get_stack_frame(bt, eip, esp);
> > + } else
> > + machdep->get_stack_frame(bt, eip, esp);
> > +
> > + bt->flags &= ~BT_NO_PRINT_REGS;
> > +
> > + bt->instptr = *eip;
> > + bt->stkptr = *esp;
> > +}
> > +
> > /*
> > * Store the head of the kernel module list for future use.
> > diff --git a/ppc64.c b/ppc64.c
> > index e8930a139e0d..f5b0b7241ea4 100644
> > --- a/ppc64.c
> > +++ b/ppc64.c
> > @@ -55,6 +55,8 @@ static void ppc64_set_bt_emergency_stack(enum
> > emergency_stack_type type,
> > static char * ppc64_check_eframe(struct ppc64_pt_regs *);
> > static void ppc64_print_eframe(char *, struct ppc64_pt_regs *,
> > struct bt_info *);
> > +int ppc64_get_cpu_reg(int cpu, int regno, const char *name, int size,
> > + void *value);
>
> As I mentioned before, we can add a 'static' keyword.
Sure. Will add it.
>
> > static void parse_cmdline_args(void);
> > static int ppc64_paca_percpu_offset_init(int);
> > static void ppc64_init_cpu_info(void);
> > @@ -704,6 +706,8 @@ ppc64_init(int when)
> > error(FATAL, "cannot malloc hwirqstack buffer
> > space.");
> > }
> > + machdep->get_cpu_reg = ppc64_get_cpu_reg;
> > +
> > ppc64_init_paca_info();
> > if (!machdep->hz) {
> > @@ -2501,6 +2505,102 @@ ppc64_print_eframe(char *efrm_str, struct
> > ppc64_pt_regs *regs,
> > ppc64_print_nip_lr(regs, 1);
> > }
> > +int
> > +ppc64_get_cpu_reg(int cpu, int regno, const char *name, int size,
> > + void *value)
> Ditto.
> > +{
> > + struct bt_info bt_info, bt_setup;
> > + struct task_context *tc;
> > + struct ppc64_pt_regs *pt_regs;
> > + ulong ip, sp;
> > +
> > + if (LIVE()) {
> > + /* doesn't support reading registers in live dump */
> > + return FALSE;
> > + }
> > +
> > + /* Currently only handling registers available in pt_regs:
> > + *
> > + * 0-31: r0-r31
> > + * 64: pc/nip
> > + * 65: msr
> > + *
> > + * 67: lr
> > + * 68: ctr
> > + */
> > + switch (regno) {
> > + case PPC64_R0_REGNUM ... PPC64_R31_REGNUM:
> > +
> > + case PPC64_PC_REGNUM:
> > + case PPC64_MSR_REGNUM:
> > + case PPC64_LR_REGNUM:
> > + case PPC64_CTR_REGNUM:
> > + break;
> > +
> > + default:
> > + // return false if we can't get that register
>
> Could you please print the 'regno' value if the given register number is not
> handled for now?
>
> if (CRASHDEBUG(1))
>
> error(WARNING, "unsupported register, regno=%d\n", regno);
>
Sure I will add that message.
> > + return FALSE;
> > + }
> > +
> > + /* FIXME: Always setting the context to CURRENT_CONTEXT irrespective of
> > whicher
> > + * thread we switched to, in gdb
> > + */
>
> The above code comment can be removed, because the latter patch will change
> this behavior.
>
> Or you could explain a little bit why to do this change in the code comment
> if needed.
Okay, sure I will remove it. I kept it signifying that it's a issue in this
patch that will be fixed later.
>
> > + tc = CURRENT_CONTEXT();
> > + BZERO(&bt_setup, sizeof(struct bt_info));
> > + clone_bt_info(&bt_setup, &bt_info, tc);
> > + fill_stackbuf(&bt_info);
> > +
> > + // reusing the get_dumpfile_regs function to get pt regs structure
> > + get_dumpfile_regs(&bt_info, &sp, &ip);
> > + pt_regs = (struct ppc64_pt_regs *)bt_info.machdep;
> > +
> > + if (!pt_regs) {
> > + error(WARNING, "pt_regs not available for cpu %d\n", cpu);
> > + return FALSE;
> > + }
> > +
> > + switch (regno) {
> > + case PPC64_R0_REGNUM ... PPC64_R31_REGNUM:
> > + if (size != sizeof(pt_regs->gpr[regno]))
> > + return FALSE; // size mismatch
> > +
> > + memcpy(value, &pt_regs->gpr[regno], size);
> > + return TRUE;
> > +
> > + case PPC64_PC_REGNUM:
> > + if (size != sizeof(pt_regs->nip))
> > + return FALSE; // size mismatch
> > +
> > + memcpy(value, &pt_regs->nip, size);
> > + return TRUE;
> > +
> > + case PPC64_MSR_REGNUM:
> > + if (size != sizeof(pt_regs->msr))
> > + return FALSE; // size mismatch
> > +
> > + memcpy(value, &pt_regs->msr, size);
> > + return TRUE;
> > +
> > + case PPC64_LR_REGNUM:
> > + if (size != sizeof(pt_regs->link))
> > + return FALSE; // size mismatch
> > +
> > + memcpy(value, &pt_regs->link, size);
> > + return TRUE;
> > +
> > + case PPC64_CTR_REGNUM:
> > + if (size != sizeof(pt_regs->ctr))
> > + return FALSE; // size mismatch
> > +
> > + memcpy(value, &pt_regs->ctr, size);
> > + return TRUE;
> > + }
> > +
> > + printf("error: %s: statement after switch case should be unreachable"
> > + , __func__);
> > + return FALSE;
>
> I would suggest the following changes:
>
> ...
> switch (regno) {
> + case PPC64_R0_REGNUM ... PPC64_R31_REGNUM:
> + if (size != sizeof(pt_regs->gpr[regno]))
> + return FALSE;
> +
> + memcpy(value, &pt_regs->gpr[regno], size);
> + break;
> + case...
> +}
> +return TRUE;
> +}
Makes sense, sure I will move the returns to end, and break instead.
>
>
> The 'printf' and 'return FALSE' should not be reached. I guess this is
> debugging information, if 'yes', we can remove it this time.
Sure, I will remove it.
Thanks,
Aditya Gupta
>
> Thanks
> Lianbo
>
> > +}
> > +
> > /*
> > * For vmcore typically saved with KDump or FADump, get SP and IP values
> > * from the saved ptregs.
> > @@ -2613,9 +2713,11 @@ ppc64_get_dumpfile_stack_frame(struct bt_info
> > *bt_in, ulong *nip, ulong *ksp)
> > pt_regs = (struct ppc64_pt_regs *)bt->machdep;
> > ur_nip = pt_regs->nip;
> > ur_ksp = pt_regs->gpr[1];
> > - /* Print the collected regs for panic task. */
> > - ppc64_print_regs(pt_regs);
> > - ppc64_print_nip_lr(pt_regs, 1);
> > + if (!(bt->flags & BT_NO_PRINT_REGS)) {
> > + /* Print the collected regs for panic task. */
> > + ppc64_print_regs(pt_regs);
> > + ppc64_print_nip_lr(pt_regs, 1);
> > + }
> > } else if ((pc->flags & KDUMP) ||
> > ((pc->flags & DISKDUMP) &&
> > (*diskdump_flags & KDUMP_CMPRS_LOCAL))) {
>
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