Hi Tao,
I need to see if there is any existing code in crash which is doing it.
I would like to avoid wheel reinvention.
For just stack unwinding, IP/SP is enough. But to see function arguments and local variables
I would like to avoid wheel reinvention.
For just stack unwinding, IP/SP is enough. But to see function arguments and local variables
especially lower frames, gdb needs to know other GPRs.
inactive_task_frame does not use pt_regs layout for saved registers and from the latest Linux sources
__switch_to_asm() does not provide dwarf/debug annotations regarding where the registers
were saved. That's why I ended up with an inactive_task_frame parsing implementation.
About other kernel versions, I need to see how it has evolved over time. AFAIR, at some point
About other kernel versions, I need to see how it has evolved over time. AFAIR, at some point
in the past it was pt_regs based.
Thanks,
Thanks,
--Alexey
On Tue, Mar 26, 2024 at 2:14 AM Tao Liu <ltao@xxxxxxxxxx> wrote:
Hi Alexey,
For the rest of the patch, I didn't see any problem. But since it only
supports modern kernels, could you please implement the rest, so I can
have a testing for variety versions of kernels(ranging from 2.6.x to
5.x), in order to find if there are further problems.
Thanks,
Tao Liu
On Mon, Mar 25, 2024 at 11:34 AM Tao Liu <ltao@xxxxxxxxxx> wrote:
>
> Hi Alexey,
>
> On Fri, Mar 22, 2024 at 7:20 AM Alexey Makhalov
> <alexey.makhalov@xxxxxxxxxxxx> wrote:
> >
> > Hi folks, please take a look on v2 of this patch and give it a try.
> > IMHO, Only remaining piece is to clean up x86_64_get_current_task_reg
> > around getting pt_regs.
> >
> > Things done:
> > 1. Rename machdep->get_cpu_reg to machdep->get_current_task_reg and rename
> > x86_64_get_cpu_reg to x86_64_get_current_task_reg, plus corresponding changes
> > for arm64 and ppc64.
> > 2. Untied gdb's TPID from any tasks or CPUs ID. Always use CURRENT_CONTEXT
> > for regs and properties fetching.
> > 3. When CURRENT switched, gdb_change_thread_context() must be called to
> > invalidate caches.
> > 4. Update x86_64_get_current_task_reg to support inactive tasks for offline
> > debugging.
> > 5. Fixed frame selection issue. It was caused by multiple calls of set_context()
> > which calls gdb_change_thread_context() unnecessarily dropping gdb caches.
> >
> > TODO:
> > 1. x86_64_get_current_task_reg is questionable about fetching pt_regs for
> > inactive tasks. How do you gyus get pt_regs structure on modern linux kernels?
> > PS: I added my approach. More testing required.
> >
> > Known issues
> > 1. After switching from all tasks to one thread:
> > b. unwinding started to work differently around top (garbaged) frames - Not quite
> > an issue for me.
> >
> > Signed-off-by: Alexey Makhalov <alexey.makhalov@xxxxxxxxxxxx>
> > ---
> > arm64.c | 4 ++--
> > crash_target.c | 48 ++++++++++++++++++-------------------
> > defs.h | 10 +++-----
> > gdb_interface.c | 8 +++----
> > kernel.c | 23 ------------------
> > ppc64.c | 8 +++----
> > task.c | 16 ++++---------
> > x86_64.c | 64 ++++++++++++++++++++++++++++++++++++++++++++-----
> > 8 files changed, 99 insertions(+), 82 deletions(-)
> >
> > diff --git a/arm64.c b/arm64.c
> > index 8ff10bf..340db2d 100644
> > --- a/arm64.c
> > +++ b/arm64.c
> > @@ -153,7 +153,7 @@ static void arm64_calc_kernel_start(void)
> > }
> >
> > static int
> > -arm64_get_cpu_reg(int cpu, int regno, const char *name,
> > +arm64_get_current_task_reg(int regno, const char *name,
> > int size, void *value)
> > {
> > struct bt_info bt_info, bt_setup;
> > @@ -511,7 +511,7 @@ arm64_init(int when)
> > machdep->dumpfile_init = NULL;
> > machdep->verify_line_number = NULL;
> > machdep->init_kernel_pgd = arm64_init_kernel_pgd;
> > - machdep->get_cpu_reg = arm64_get_cpu_reg;
> > + machdep->get_current_task_reg = arm64_get_current_task_reg;
> >
> > /* use machdep parameters */
> > arm64_calc_phys_offset();
> > diff --git a/crash_target.c b/crash_target.c
> > index fb3b634..6e96506 100644
> > --- a/crash_target.c
> > +++ b/crash_target.c
> > @@ -26,11 +26,8 @@
> > void crash_target_init (void);
> >
> > extern "C" int gdb_readmem_callback(unsigned long, void *, int, int);
> > -extern "C" int crash_get_cpu_reg (int cpu, int regno, const char *regname,
> > +extern "C" int crash_get_current_task_reg (int regno, const char *regname,
> > int regsize, void *val);
> > -extern "C" void gdb_refresh_regcache(unsigned int cpu);
> > -extern "C" int set_cpu(int cpu, int print_context);
> > -extern "C" int crash_set_thread(ulong);
> > extern "C" int gdb_change_thread_context (ulong);
> > extern "C" void crash_get_current_task_info(unsigned long *pid, char **comm);
> >
> > @@ -72,22 +69,27 @@ public:
> >
> > };
> >
> > -/* We just get all the registers, so we don't use regno. */
> > void
> > crash_target::fetch_registers (struct regcache *regcache, int regno)
> > {
> > + int r;
> > gdb_byte regval[16];
> > - int cpu = inferior_ptid.tid();
> > struct gdbarch *arch = regcache->arch ();
> >
> > - for (int r = 0; r < gdbarch_num_regs (arch); r++)
> > + if (regno >= 0) {
> > + r = regno;
> > + goto onetime;
> > + }
> > +
> > + for (r = 0; regno == -1 && r < gdbarch_num_regs (arch); r++)
> > {
> > +onetime:
> > const char *regname = gdbarch_register_name(arch, r);
> > int regsize = register_size (arch, r);
> > if (regsize > sizeof (regval))
> > error (_("fatal error: buffer size is not enough to fit register value"));
> >
> > - if (crash_get_cpu_reg (cpu, r, regname, regsize, (void *)®val))
> > + if (crash_get_current_task_reg (r, regname, regsize, (void *)®val))
> > regcache->raw_supply (r, regval);
> > else
> > regcache->raw_supply (r, NULL);
> > @@ -142,19 +144,17 @@ crash_target_init (void)
> > extern "C" int
> > gdb_change_thread_context (ulong task)
> > {
> > - inferior* inf = current_inferior();
> > - int cpu = crash_set_thread(task);
> > - if (cpu < 0)
> > - return FALSE;
> > -
> > - ptid_t ptid = ptid_t(CRASH_INFERIOR_PID, 0, cpu);
> > - thread_info *tp = find_thread_ptid (inf, ptid);
> > -
> > - if (tp == nullptr)
> > - return FALSE;
> > -
> > - target_fetch_registers(get_thread_regcache(tp), -1);
> > - switch_to_thread(tp);
> > - reinit_frame_cache ();
> > - return TRUE;
> > -}
> > \ No newline at end of file
> > + static ulong prev_task = 0;
> > +
> > + /*
> > + * Crash calls this method even if CURRENT task is not updated.
> > + * Ignore it and keep gdb caches active.
> > + */
> > + if (task == prev_task)
> > + return TRUE;
> > + prev_task = task;
> > +
> > + registers_changed();
> > + reinit_frame_cache();
> > + return TRUE;
> > +}
> > diff --git a/defs.h b/defs.h
> > index d7e3b18..7596179 100644
> > --- a/defs.h
> > +++ b/defs.h
> > @@ -1081,7 +1081,7 @@ struct machdep_table {
> > void (*get_irq_affinity)(int);
> > void (*show_interrupts)(int, ulong *);
> > int (*is_page_ptr)(ulong, physaddr_t *);
> > - int (*get_cpu_reg)(int, int, const char *, int, void *);
> > + int (*get_current_task_reg)(int, const char *, int, void *);
> > int (*is_cpu_prstatus_valid)(int cpu);
> > };
> >
> > @@ -6124,7 +6124,6 @@ void dump_kernel_table(int);
> > void dump_bt_info(struct bt_info *, char *where);
> > void dump_log(int);
> > void parse_kernel_version(char *);
> > -int crash_set_thread(ulong);
> >
> > #define LOG_LEVEL(v) ((v) & 0x07)
> > #define SHOW_LOG_LEVEL (0x1)
> > @@ -8023,7 +8022,7 @@ extern int have_full_symbols(void);
> >
> > /*
> > * Register numbers must be in sync with gdb/features/i386/64bit-core.c
> > - * to make crash_target->fetch_registers() ---> machdep->get_cpu_reg()
> > + * to make crash_target->fetch_registers() ---> machdep->get_current_task_reg()
> > * working properly.
> > */
> > enum x86_64_regnum {
> > @@ -8081,7 +8080,7 @@ enum arm64_regnum {
> >
> > /*
> > * Register numbers to make crash_target->fetch_registers()
> > - * ---> machdep->get_cpu_reg() work properly.
> > + * ---> 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
> > @@ -8199,7 +8198,4 @@ enum ppc64_regnum {
> > PPC64_VRSAVE_REGNU = 139
> > };
> >
> > -/* crash_target.c */
> > -extern void gdb_refresh_regcache (unsigned int cpu);
> > -
> > #endif /* !GDB_COMMON */
> > diff --git a/gdb_interface.c b/gdb_interface.c
> > index 28264c2..2e9117a 100644
> > --- a/gdb_interface.c
> > +++ b/gdb_interface.c
> > @@ -1073,14 +1073,14 @@ unsigned long crash_get_kaslr_offset(void)
> > }
> >
> > /* Callbacks for crash_target */
> > -int crash_get_cpu_reg (int cpu, int regno, const char *regname,
> > +int crash_get_current_task_reg (int regno, const char *regname,
> > int regsize, void *val);
> >
> > -int crash_get_cpu_reg (int cpu, int regno, const char *regname,
> > +int crash_get_current_task_reg (int regno, const char *regname,
> > int regsize, void *value)
> > {
> > - if (!machdep->get_cpu_reg)
> > + if (!machdep->get_current_task_reg)
> > return FALSE;
> > - return machdep->get_cpu_reg(cpu, regno, regname, regsize, value);
> > + return machdep->get_current_task_reg(regno, regname, regsize, value);
> > }
> >
> > diff --git a/kernel.c b/kernel.c
> > index 446fd78..15b00dc 100644
> > --- a/kernel.c
> > +++ b/kernel.c
> > @@ -6543,29 +6543,6 @@ set_cpu(int cpu, int print_context)
> > show_context(CURRENT_CONTEXT());
> > }
> >
> > -int
> > -crash_set_thread(ulong task)
> > -{
> > - bool found = FALSE;
> > - struct task_context *tc = FIRST_CONTEXT();
> > -
> > - for (int i = 0; i < RUNNING_TASKS(); i++, tc++) {
> > - if (tc->task == task) {
> > - found = TRUE;
> > - break;
> > - }
> > - }
> > -
> > - if (!found)
> > - return -1;
> > -
> > - if (CURRENT_TASK() == tc->task)
> > - return 0;
> > -
> > - set_context(tc->task, NO_PID, TRUE);
> > - return 0;
> > -}
> > -
> > /*
> > * Collect the irq_desc[] entry along with its associated handler and
> > * action structures.
> > diff --git a/ppc64.c b/ppc64.c
> > index a87e621..aeccb70 100644
> > --- a/ppc64.c
> > +++ b/ppc64.c
> > @@ -55,7 +55,7 @@ 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,
> > +static int ppc64_get_current_task_reg(int regno, const char *name, int size,
> > void *value);
> > static void parse_cmdline_args(void);
> > static int ppc64_paca_percpu_offset_init(int);
> > @@ -706,7 +706,7 @@ ppc64_init(int when)
> > error(FATAL, "cannot malloc hwirqstack buffer space.");
> > }
> >
> > - machdep->get_cpu_reg = ppc64_get_cpu_reg;
> > + machdep->get_current_task_reg = ppc64_get_current_task_reg;
> >
> > ppc64_init_paca_info();
> >
> > @@ -2506,7 +2506,7 @@ ppc64_print_eframe(char *efrm_str, struct ppc64_pt_regs *regs,
> > }
> >
> > static int
> > -ppc64_get_cpu_reg(int cpu, int regno, const char *name, int size,
> > +ppc64_get_current_task_reg(int regno, const char *name, int size,
> > void *value)
> > {
> > struct bt_info bt_info, bt_setup;
> > @@ -2555,7 +2555,7 @@ ppc64_get_cpu_reg(int cpu, int regno, const char *name, int size,
> > pt_regs = (struct ppc64_pt_regs *)bt_info.machdep;
> >
> > if (!pt_regs) {
> > - error(WARNING, "pt_regs not available for cpu %d\n", cpu);
> > + error(WARNING, "pt_regs not available for cpu %d\n", tc->processor);
> > return FALSE;
> > }
> >
> > diff --git a/task.c b/task.c
> > index f7e5b05..5f1ddad 100644
> > --- a/task.c
> > +++ b/task.c
> > @@ -11286,19 +11286,11 @@ check_stack_end_magic:
> > fprintf(fp, "No stack overflows detected\n");
> > }
> >
> > +void crash_get_current_task_info(unsigned long *pid, char **comm);
> > void crash_get_current_task_info(unsigned long *pid, char **comm)
> > {
> > - int i;
> > - struct task_context *tc;
> > + struct task_context *tc = CURRENT_CONTEXT();
> >
> > - tc = FIRST_CONTEXT();
> > - for (i = 0; i < RUNNING_TASKS(); i++, tc++)
> > - if (tc->task == CURRENT_TASK()) {
> > - *pid = tc->pid;
> > - *comm = tc->comm;
> > - return;
> > - }
> > - *pid = 0;
> > - *comm = NULL;
> > - return;
> > + *pid = tc->pid;
> > + *comm = tc->comm;
> > }
> > diff --git a/x86_64.c b/x86_64.c
> > index 41e67c6..73bb353 100644
> > --- a/x86_64.c
> > +++ b/x86_64.c
> > @@ -126,7 +126,7 @@ static int x86_64_get_framesize(struct bt_info *, ulong, ulong, char *);
> > static void x86_64_framesize_debug(struct bt_info *);
> > static void x86_64_get_active_set(void);
> > static int x86_64_get_kvaddr_ranges(struct vaddr_range *);
> > -static int x86_64_get_cpu_reg(int, int, const char *, int, void *);
> > +static int x86_64_get_current_task_reg(int, const char *, int, void *);
> > static int x86_64_verify_paddr(uint64_t);
> > static void GART_init(void);
> > static void x86_64_exception_stacks_init(void);
> > @@ -207,7 +207,7 @@ x86_64_init(int when)
> > machdep->machspec->irq_eframe_link = UNINITIALIZED;
> > machdep->machspec->irq_stack_gap = UNINITIALIZED;
> > machdep->get_kvaddr_ranges = x86_64_get_kvaddr_ranges;
> > - machdep->get_cpu_reg = x86_64_get_cpu_reg;
> > + machdep->get_current_task_reg = x86_64_get_current_task_reg;
> > if (machdep->cmdline_args[0])
> > parse_cmdline_args();
> > if ((string = pc->read_vmcoreinfo("relocate"))) {
> > @@ -898,7 +898,7 @@ x86_64_dump_machdep_table(ulong arg)
> > fprintf(fp, " is_page_ptr: x86_64_is_page_ptr()\n");
> > fprintf(fp, " verify_paddr: x86_64_verify_paddr()\n");
> > fprintf(fp, " get_kvaddr_ranges: x86_64_get_kvaddr_ranges()\n");
> > - fprintf(fp, " get_cpu_reg: x86_64_get_cpu_reg()\n");
> > + fprintf(fp, "get_current_task_reg: x86_64_get_current_task_reg()\n");
> > fprintf(fp, " init_kernel_pgd: x86_64_init_kernel_pgd()\n");
> > fprintf(fp, "clear_machdep_cache: x86_64_clear_machdep_cache()\n");
> > fprintf(fp, " xendump_p2m_create: %s\n", PVOPS_XEN() ?
> > @@ -9186,7 +9186,7 @@ x86_64_get_kvaddr_ranges(struct vaddr_range *vrp)
> > }
> >
> > static int
> > -x86_64_get_cpu_reg(int cpu, int regno, const char *name,
> > +x86_64_get_current_task_reg(int regno, const char *name,
> > int size, void *value)
> > {
> > struct bt_info bt_info, bt_setup;
> > @@ -9195,8 +9195,6 @@ x86_64_get_cpu_reg(int cpu, int regno, const char *name,
> > ulong ip, sp;
> > bool ret = FALSE;
> >
> > - if (VMSS_DUMPFILE())
> > - return vmware_vmss_get_cpu_reg(cpu, regno, name, size, value);
> > switch (regno) {
> > case RAX_REGNUM ... GS_REGNUM:
> > case FS_BASE_REGNUM ... ORIG_RAX_REGNUM:
> > @@ -9208,6 +9206,60 @@ x86_64_get_cpu_reg(int cpu, int regno, const char *name,
> > tc = CURRENT_CONTEXT();
> > if (!tc)
> > return FALSE;
> > +
> > + /*
> > + * For inactive task, grab rip, rbp, rbx, r12, r13, r14 and r15 from
> > + * inactive_task_frame (see __switch_to_asm). Other regs saved on
> > + * regular frame.
> > + */
> > + if (!is_task_active(tc->task)) {
> > + int frame_size = STRUCT_SIZE("inactive_task_frame");
> > +
> > + /* Only modern kernels supported. */
> > + if (tt->flags & THREAD_INFO && frame_size == 7 * 8) {
> > + ulong rsp;
> > + int offset = 0;
> > + switch (regno) {
> > + case RSP_REGNUM:
> > + readmem(tc->task + OFFSET(task_struct_thread) +
> > + OFFSET(thread_struct_rsp), KVADDR,
> > + &rsp, sizeof(void *),
> > + "thread_struct rsp", FAULT_ON_ERROR);
> > + rsp += frame_size;
> > + memcpy(value, &rsp, size);
> > + return TRUE;
> > + case RIP_REGNUM:
> > + offset += 8;
> > + case RBP_REGNUM:
> > + offset += 8;
> > + case RBX_REGNUM:
> > + offset += 8;
> > + case R12_REGNUM:
> > + offset += 8;
> > + case R13_REGNUM:
> > + offset += 8;
> > + case R14_REGNUM:
> > + offset += 8;
> > + case R15_REGNUM:
> > + readmem(tc->task + OFFSET(task_struct_thread) +
> > + OFFSET(thread_struct_rsp), KVADDR,
> > + &rsp, sizeof(void *),
> > + "thread_struct rsp", FAULT_ON_ERROR);
> > + readmem(rsp + offset, KVADDR, value, sizeof(void *),
> > + "inactive_thread_frame saved regs", FAULT_ON_ERROR);
> > + return TRUE;
> > + }
>
> For this part, it looks similar to what
> x86_64.c:x86_64_get_stack_frame():5016 is trying to do, which is
> extracting reg values from stack. Is there a special consideration to
> put it in here?
>
> IMHO, the x86_64_get_stack_frame() is responsible for extracting reg
> values from stack frame or elf notes(aka the regs value reproducer).
> And it will give a universal data structure, aka pt_regs, to
> x86_64_get_current_task_reg() (aka the regs value consumer).
>
> In this design, the x86_64_get_current_task_reg() is decoupled from
> stack, no matter inactive_task_frame or traditional linked list stack
> frame or active tasks regs coming from elf notes, the consumer won't
> care, all it need is a pt_regs structure and get values from it.
> Personally I prefer this design. Any comments?
>
> For other parts of the patch, I'm still reviewing and testing.
>
> Thanks,
> Tao Liu
>
> > + }
> > + /* TBD: older kernels support. */
> > + return FALSE;
> > + }
> > +
> > + /*
> > + * Task is active, grab CPU's registers
> > + */
> > + if (VMSS_DUMPFILE())
> > + return vmware_vmss_get_cpu_reg(tc->processor, regno, name, size, value);
> > +
> > BZERO(&bt_setup, sizeof(struct bt_info));
> > clone_bt_info(&bt_setup, &bt_info, tc);
> > fill_stackbuf(&bt_info);
> > --
> > 2.39.0
> >
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