[Crash-utility] Re: [[PATCH v2]] Clean up on top of one-thread-v2

Hi Alexey, On Fri, Mar 22, 2024 at 7:20 AM Alexey Makhalov <alexey.makhalov(a)broadcom.com&gt; 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(a)broadcom.com&gt; > --- > 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 *)&regval)) > + if (crash_get_current_task_reg (r, regname, regsize, (void *)&regval)) > 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 >