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ppc64: correct gdb passthroughs by implementing machdep->get_cpu_reg
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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
    crash-utility#1  __crash_kexec (regs=<optimized out>) at kernel/kexec_core.c:974
    crash-utility#2  0xc000000000168918 in panic (fmt=<optimized out>) at kernel/panic.c:358
    crash-utility#3  0xc000000000b735f8 in sysrq_handle_crash (key=<optimized out>) at drivers/tty/sysrq.c:155
    crash-utility#4  0xc000000000b742cc in __handle_sysrq (key=key@entry=99, check_mask=check_mask@entry=false) at drivers/tty/sysrq.c:602
    crash-utility#5  0xc000000000b7506c in write_sysrq_trigger (file=<optimized out>, buf=<optimized out>, count=2, ppos=<optimized out>) at drivers/tty/sysrq.c:1163
    crash-utility#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
    crash-utility#7  proc_reg_write (file=<optimized out>, buf=<optimized out>, count=<optimized out>, ppos=<optimized out>) at fs/proc/inode.c:352
    crash-utility#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

Cc: Sourabh Jain <[email protected]>
Cc: Hari Bathini <[email protected]>
Cc: Mahesh J Salgaonkar <[email protected]>
Cc: Naveen N. Rao <[email protected]>
Cc: Lianbo Jiang <[email protected]>
Cc: HAGIO KAZUHITO(萩尾 一仁) <[email protected]>
Improved-by: Tao Liu <[email protected]>
Signed-off-by: Aditya Gupta <[email protected]>
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adi-g15-ibm committed Mar 29, 2024
1 parent c5a7ecf commit 40691e9
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123 changes: 123 additions & 0 deletions defs.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -982,6 +982,7 @@ struct bt_info {
ulong eframe_ip;
ulong radix;
ulong *cpumask;
bool need_free;
};

#define STACK_OFFSET_TYPE(OFF) \
Expand Down Expand Up @@ -6095,6 +6096,7 @@ 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 *);
Expand Down Expand Up @@ -6195,6 +6197,7 @@ 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)
Expand Down Expand Up @@ -8052,6 +8055,126 @@ 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
*/
enum ppc64_regnum {
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
};

/* crash_target.c */
extern int gdb_change_thread_context (ulong task);

Expand Down
33 changes: 33 additions & 0 deletions kernel.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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.
Expand Down
126 changes: 119 additions & 7 deletions ppc64.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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 *);
static int ppc64_get_cpu_reg(int cpu, int regno, const char *name, int size,
void *value);
static void parse_cmdline_args(void);
static int ppc64_paca_percpu_offset_init(int);
static void ppc64_init_cpu_info(void);
Expand Down Expand Up @@ -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) {
Expand Down Expand Up @@ -2501,6 +2505,104 @@ ppc64_print_eframe(char *efrm_str, struct ppc64_pt_regs *regs,
ppc64_print_nip_lr(regs, 1);
}

static int
ppc64_get_cpu_reg(int cpu, int regno, const char *name, int size,
void *value)
{
struct bt_info bt_info, bt_setup;
struct task_context *tc;
ulong task;
struct ppc64_pt_regs *pt_regs;
ulong ip, sp;
bool ret = FALSE;

/* Currently only handling registers available in ppc64_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
if (CRASHDEBUG(1))
error(WARNING, "unsupported register, regno=%d\n", regno);
return FALSE;
}

tc = CURRENT_CONTEXT();
if (!tc)
return FALSE;
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);
if (bt_info.stackbuf)
FREEBUF(bt_info.stackbuf);
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])) {
ret = FALSE; break; // size mismatch
}
memcpy(value, &pt_regs->gpr[regno], size);
ret = TRUE; break;

case PPC64_PC_REGNUM:
if (size != sizeof(pt_regs->nip)) {
ret = FALSE; break; // size mismatch
}
memcpy(value, &pt_regs->nip, size);
ret = TRUE; break;

case PPC64_MSR_REGNUM:
if (size != sizeof(pt_regs->msr)) {
ret = FALSE; break; // size mismatch
}
memcpy(value, &pt_regs->msr, size);
ret = TRUE; break;

case PPC64_LR_REGNUM:
if (size != sizeof(pt_regs->link)) {
ret = FALSE; break; // size mismatch
}
memcpy(value, &pt_regs->link, size);
ret = TRUE; break;

case PPC64_CTR_REGNUM:
if (size != sizeof(pt_regs->ctr)) {
ret = FALSE; break; // size mismatch
}
memcpy(value, &pt_regs->ctr, size);
ret = TRUE; break;
}
if (bt_info.need_free) {
FREEBUF(pt_regs);
bt_info.need_free = FALSE;
}

return ret;
}

/*
* For vmcore typically saved with KDump or FADump, get SP and IP values
* from the saved ptregs.
Expand Down Expand Up @@ -2613,9 +2715,11 @@ 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))) {
Expand Down Expand Up @@ -2779,19 +2883,27 @@ static void
ppc64_get_stack_frame(struct bt_info *bt, ulong *pcp, ulong *spp)
{
ulong ksp, nip;

struct ppc64_pt_regs *regs;

nip = ksp = 0;

if (DUMPFILE() && is_task_active(bt->task))
if (DUMPFILE() && is_task_active(bt->task)) {
ppc64_get_dumpfile_stack_frame(bt, &nip, &ksp);
else
bt->need_free = FALSE;
} else {
get_ppc64_frame(bt, &nip, &ksp);
regs = (struct ppc64_pt_regs *)GETBUF(sizeof(struct ppc64_pt_regs));
memset(regs, 0, sizeof(struct ppc64_pt_regs));
regs->nip = nip;
regs->gpr[1] = ksp;
bt->machdep = regs;
bt->need_free = TRUE;
}

if (pcp)
*pcp = nip;
if (spp)
*spp = ksp;

}

static ulong
Expand Down

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