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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]>
Cc: Tao Liu <[email protected]>
Cc: Alexey Makhalov <[email protected]>
Improved-by: Tao Liu <[email protected]>
Signed-off-by: Aditya Gupta <[email protected]>
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adi-g15-ibm committed Jul 31, 2024
1 parent 771602e commit 43625f8
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Showing 4 changed files with 331 additions and 11 deletions.
130 changes: 130 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 @@ -6102,6 +6103,7 @@ 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 @@ -6201,6 +6203,7 @@ 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 @@ -8007,6 +8010,13 @@ extern int have_full_symbols(void);
#define XEN_HYPERVISOR_ARCH
#endif

#ifndef offsetof
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
#endif
#define FIELD_SIZEOF(t, f) (sizeof(((t*)0)->f))
#define REG_SEQ(TYPE, MEMBER) \
(offsetof(struct TYPE, MEMBER) / FIELD_SIZEOF(struct TYPE, MEMBER))

/*
* Register numbers must be in sync with gdb/features/i386/64bit-core.c
* to make crash_target->fetch_registers() ---> machdep->get_cpu_reg()
Expand Down Expand Up @@ -8056,6 +8066,126 @@ enum x86_64_regnum {
LAST_REGNUM
};

/*
* Register numbers to make crash_target->fetch_registers()
* ---> machdep->get_current_task_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 (void);

Expand Down
33 changes: 33 additions & 0 deletions kernel.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3534,6 +3534,39 @@ 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
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