From 5f5ddfb3605d2a4f555a7ff034859e623eafcd27 Mon Sep 17 00:00:00 2001 From: Jason Wessel Date: Fri, 1 Aug 2008 08:39:34 -0500 Subject: [PATCH 1/3] kgdb: remove the requirement for CONFIG_FRAME_POINTER There is no technical reason that the kgdb core requires frame pointers. It is up to the end user of KGDB to decide if they need them or not. [ anemo@mba.ocn.ne.jp: removed frame pointers on mips ] Signed-off-by: Jason Wessel --- Documentation/DocBook/kgdb.tmpl | 8 ++++++++ lib/Kconfig.kgdb | 11 +++++++---- 2 files changed, 15 insertions(+), 4 deletions(-) diff --git a/Documentation/DocBook/kgdb.tmpl b/Documentation/DocBook/kgdb.tmpl index e8acd1f0345..54d3b158d08 100644 --- a/Documentation/DocBook/kgdb.tmpl +++ b/Documentation/DocBook/kgdb.tmpl @@ -98,6 +98,14 @@ "Kernel debugging" select "KGDB: kernel debugging with remote gdb". + It is advised, but not required that you turn on the + CONFIG_FRAME_POINTER kernel option. This option inserts code to + into the compiled executable which saves the frame information in + registers or on the stack at different points which will allow a + debugger such as gdb to more accurately construct stack back traces + while debugging the kernel. + + Next you should choose one of more I/O drivers to interconnect debugging host and debugged target. Early boot debugging requires a KGDB I/O driver that supports early debugging and the driver must be diff --git a/lib/Kconfig.kgdb b/lib/Kconfig.kgdb index 2cfd2721f7e..9b5d1d7f2ef 100644 --- a/lib/Kconfig.kgdb +++ b/lib/Kconfig.kgdb @@ -4,14 +4,17 @@ config HAVE_ARCH_KGDB menuconfig KGDB bool "KGDB: kernel debugging with remote gdb" - select FRAME_POINTER depends on HAVE_ARCH_KGDB depends on DEBUG_KERNEL && EXPERIMENTAL help If you say Y here, it will be possible to remotely debug the - kernel using gdb. Documentation of kernel debugger is available - at http://kgdb.sourceforge.net as well as in DocBook form - in Documentation/DocBook/. If unsure, say N. + kernel using gdb. It is recommended but not required, that + you also turn on the kernel config option + CONFIG_FRAME_POINTER to aid in producing more reliable stack + backtraces in the external debugger. Documentation of + kernel debugger is available at http://kgdb.sourceforge.net + as well as in DocBook form in Documentation/DocBook/. If + unsure, say N. if KGDB From a9b60bf4c29e07a5a2f26a6f74937972fee9b58b Mon Sep 17 00:00:00 2001 From: Jason Wessel Date: Fri, 1 Aug 2008 08:39:34 -0500 Subject: [PATCH 2/3] kgdb: fix kgdb_validate_break_address to perform a mem write A regression to the kgdb core was found in the case of using the CONFIG_DEBUG_RODATA kernel option. When this option is on, a breakpoint cannot be written into any readonly memory page. When an external debugger requests a breakpoint to get set, the kgdb_validate_break_address() was only checking to see if the address to place the breakpoint was readable and lacked a write check. This patch changes the validate routine to try reading (via the breakpoint set request) and also to try immediately writing the break point. If either fails, an error is correctly returned and the debugger behaves correctly. Then an end user can make the descision to use hardware breakpoints. Also update the documentation to reflect that using CONFIG_DEBUG_RODATA will inhibit the use of software breakpoints. Signed-off-by: Jason Wessel --- Documentation/DocBook/kgdb.tmpl | 10 ++++++++++ kernel/kgdb.c | 26 +++++++++++++++++++------- 2 files changed, 29 insertions(+), 7 deletions(-) diff --git a/Documentation/DocBook/kgdb.tmpl b/Documentation/DocBook/kgdb.tmpl index 54d3b158d08..372dec20c8d 100644 --- a/Documentation/DocBook/kgdb.tmpl +++ b/Documentation/DocBook/kgdb.tmpl @@ -106,6 +106,16 @@ while debugging the kernel. + If the architecture that you are using supports the kernel option + CONFIG_DEBUG_RODATA, you should consider turning it off. This + option will prevent the use of software breakpoints because it + marks certain regions of the kernel's memory space as read-only. + If kgdb supports it for the architecture you are using, you can + use hardware breakpoints if you desire to run with the + CONFIG_DEBUG_RODATA option turned on, else you need to turn off + this option. + + Next you should choose one of more I/O drivers to interconnect debugging host and debugged target. Early boot debugging requires a KGDB I/O driver that supports early debugging and the driver must be diff --git a/kernel/kgdb.c b/kernel/kgdb.c index 3ec23c3ec97..c0d45b2c4d7 100644 --- a/kernel/kgdb.c +++ b/kernel/kgdb.c @@ -166,13 +166,6 @@ early_param("nokgdbroundup", opt_nokgdbroundup); * Weak aliases for breakpoint management, * can be overriden by architectures when needed: */ -int __weak kgdb_validate_break_address(unsigned long addr) -{ - char tmp_variable[BREAK_INSTR_SIZE]; - - return probe_kernel_read(tmp_variable, (char *)addr, BREAK_INSTR_SIZE); -} - int __weak kgdb_arch_set_breakpoint(unsigned long addr, char *saved_instr) { int err; @@ -191,6 +184,25 @@ int __weak kgdb_arch_remove_breakpoint(unsigned long addr, char *bundle) (char *)bundle, BREAK_INSTR_SIZE); } +int __weak kgdb_validate_break_address(unsigned long addr) +{ + char tmp_variable[BREAK_INSTR_SIZE]; + int err; + /* Validate setting the breakpoint and then removing it. In the + * remove fails, the kernel needs to emit a bad message because we + * are deep trouble not being able to put things back the way we + * found them. + */ + err = kgdb_arch_set_breakpoint(addr, tmp_variable); + if (err) + return err; + err = kgdb_arch_remove_breakpoint(addr, tmp_variable); + if (err) + printk(KERN_ERR "KGDB: Critical breakpoint error, kernel " + "memory destroyed at: %lx", addr); + return err; +} + unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs) { return instruction_pointer(regs); From 25fc999913839a45cbb48ac7872e67f7521e7ed9 Mon Sep 17 00:00:00 2001 From: Jason Wessel Date: Fri, 1 Aug 2008 08:39:35 -0500 Subject: [PATCH 3/3] kgdb: fix gdb serial thread queries The command "info threads" did not work correctly with kgdb. It would result in a silent kernel hang if used. This patach addresses several problems. - Fix use of deprecated NR_CPUS - Fix kgdb to not walk linearly through the pid space - Correctly implement shadow pids - Change the threads per query to a #define - Fix kgdb_hex2long to work with negated values The threads 0 and -1 are reserved to represent the current task. That means that CPU 0 will start with a shadow thread id of -2, and CPU 1 will have a shadow thread id of -3, etc... From the debugger you can switch to a shadow thread to see what one of the other cpus was doing, however it is not possible to execute run control operations on any other cpu execept the cpu executing the kgdb_handle_exception(). Signed-off-by: Jason Wessel --- kernel/kgdb.c | 68 +++++++++++++++++++++++++++++++++++++-------------- 1 file changed, 50 insertions(+), 18 deletions(-) diff --git a/kernel/kgdb.c b/kernel/kgdb.c index c0d45b2c4d7..eaa21fc9ad1 100644 --- a/kernel/kgdb.c +++ b/kernel/kgdb.c @@ -56,12 +56,14 @@ static int kgdb_break_asap; +#define KGDB_MAX_THREAD_QUERY 17 struct kgdb_state { int ex_vector; int signo; int err_code; int cpu; int pass_exception; + unsigned long thr_query; unsigned long threadid; long kgdb_usethreadid; struct pt_regs *linux_regs; @@ -445,9 +447,14 @@ int kgdb_hex2long(char **ptr, unsigned long *long_val) { int hex_val; int num = 0; + int negate = 0; *long_val = 0; + if (**ptr == '-') { + negate = 1; + (*ptr)++; + } while (**ptr) { hex_val = hex(**ptr); if (hex_val < 0) @@ -458,6 +465,9 @@ int kgdb_hex2long(char **ptr, unsigned long *long_val) (*ptr)++; } + if (negate) + *long_val = -*long_val; + return num; } @@ -527,10 +537,16 @@ static void int_to_threadref(unsigned char *id, int value) static struct task_struct *getthread(struct pt_regs *regs, int tid) { /* - * Non-positive TIDs are remapped idle tasks: + * Non-positive TIDs are remapped to the cpu shadow information */ - if (tid <= 0) - return idle_task(-tid); + if (tid == 0 || tid == -1) + tid = -atomic_read(&kgdb_active) - 2; + if (tid < 0) { + if (kgdb_info[-tid - 2].task) + return kgdb_info[-tid - 2].task; + else + return idle_task(-tid - 2); + } /* * find_task_by_pid_ns() does not take the tasklist lock anymore @@ -737,14 +753,15 @@ setundefined: } /* - * Remap normal tasks to their real PID, idle tasks to -1 ... -NR_CPUs: + * Remap normal tasks to their real PID, + * CPU shadow threads are mapped to -CPU - 2 */ static inline int shadow_pid(int realpid) { if (realpid) return realpid; - return -1-raw_smp_processor_id(); + return -raw_smp_processor_id() - 2; } static char gdbmsgbuf[BUFMAX + 1]; @@ -838,7 +855,7 @@ static void gdb_cmd_getregs(struct kgdb_state *ks) local_debuggerinfo = kgdb_info[ks->cpu].debuggerinfo; } else { local_debuggerinfo = NULL; - for (i = 0; i < NR_CPUS; i++) { + for_each_online_cpu(i) { /* * Try to find the task on some other * or possibly this node if we do not @@ -972,10 +989,13 @@ static int gdb_cmd_reboot(struct kgdb_state *ks) /* Handle the 'q' query packets */ static void gdb_cmd_query(struct kgdb_state *ks) { - struct task_struct *thread; + struct task_struct *g; + struct task_struct *p; unsigned char thref[8]; char *ptr; int i; + int cpu; + int finished = 0; switch (remcom_in_buffer[1]) { case 's': @@ -985,22 +1005,34 @@ static void gdb_cmd_query(struct kgdb_state *ks) break; } - if (remcom_in_buffer[1] == 'f') - ks->threadid = 1; - + i = 0; remcom_out_buffer[0] = 'm'; ptr = remcom_out_buffer + 1; - - for (i = 0; i < 17; ks->threadid++) { - thread = getthread(ks->linux_regs, ks->threadid); - if (thread) { - int_to_threadref(thref, ks->threadid); + if (remcom_in_buffer[1] == 'f') { + /* Each cpu is a shadow thread */ + for_each_online_cpu(cpu) { + ks->thr_query = 0; + int_to_threadref(thref, -cpu - 2); pack_threadid(ptr, thref); ptr += BUF_THREAD_ID_SIZE; *(ptr++) = ','; i++; } } + + do_each_thread(g, p) { + if (i >= ks->thr_query && !finished) { + int_to_threadref(thref, p->pid); + pack_threadid(ptr, thref); + ptr += BUF_THREAD_ID_SIZE; + *(ptr++) = ','; + ks->thr_query++; + if (ks->thr_query % KGDB_MAX_THREAD_QUERY == 0) + finished = 1; + } + i++; + } while_each_thread(g, p); + *(--ptr) = '\0'; break; @@ -1023,15 +1055,15 @@ static void gdb_cmd_query(struct kgdb_state *ks) error_packet(remcom_out_buffer, -EINVAL); break; } - if (ks->threadid > 0) { + if ((int)ks->threadid > 0) { kgdb_mem2hex(getthread(ks->linux_regs, ks->threadid)->comm, remcom_out_buffer, 16); } else { static char tmpstr[23 + BUF_THREAD_ID_SIZE]; - sprintf(tmpstr, "Shadow task %d for pid 0", - (int)(-ks->threadid-1)); + sprintf(tmpstr, "shadowCPU%d", + (int)(-ks->threadid - 2)); kgdb_mem2hex(tmpstr, remcom_out_buffer, strlen(tmpstr)); } break;