From 6be7045c7756caf2d445dc66473e45ac5779cd55 Mon Sep 17 00:00:00 2001 From: Illia Ostapyshyn Date: Sat, 3 May 2025 14:32:31 +0200 Subject: scripts/gdb: fix kgdb probing on single-core systems Patch series "scripts/gdb: Fixes related to lx_per_cpu()". These patches (1) fix kgdb detection on systems featuring a single CPU and (2) update the documentation to reflect the current usage of lx_per_cpu() and update an outdated example of its usage. This patch (of 2): When requested the list of threads via qfThreadInfo, gdb_cmd_query in kernel/debug/gdbstub.c first returns "shadow" threads for CPUs followed by the actual tasks in the system. Extended qThreadExtraInfo queries yield "shadowCPU%d" as the name for the CPU core threads. This behavior is used by get_gdbserver_type() to probe for KGDB by matching the name for the thread 2 against "shadowCPU". This breaks down on single-core systems, where thread 2 is the first nonshadow thread. Request the name for thread 1 instead. As GDB assigns thread IDs in the order of their appearance, it is safe to assume shadowCPU0 at ID 1 as long as CPU0 is not hotplugged. Before: (gdb) info threads Id Target Id Frame 1 Thread 4294967294 (shadowCPU0) kgdb_breakpoint () * 2 Thread 1 (swapper/0) kgdb_breakpoint () 3 Thread 2 (kthreadd) 0x0000000000000000 in ?? () ... (gdb) p $lx_current().comm Sorry, obtaining the current CPU is not yet supported with this gdb server. After: (gdb) info threads Id Target Id Frame 1 Thread 4294967294 (shadowCPU0) kgdb_breakpoint () * 2 Thread 1 (swapper/0) kgdb_breakpoint () 3 Thread 2 (kthreadd) 0x0000000000000000 in ?? () ... (gdb) p $lx_current().comm $1 = "swapper/0\000\000\000\000\000\000" Link: https://lkml.kernel.org/r/20250503123234.2407184-1-illia@yshyn.com Link: https://lkml.kernel.org/r/20250503123234.2407184-2-illia@yshyn.com Signed-off-by: Illia Ostapyshyn Cc: Alex Shi Cc: Brendan Jackman Cc: Dongliang Mu Cc: Florian Rommel Cc: Hu Haowen <2023002089@link.tyut.edu.cn> Cc: Jan Kiszka Cc: Jonathan Corbet Cc: Kieran Bingham Cc: Yanteng Si Signed-off-by: Andrew Morton --- scripts/gdb/linux/utils.py | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'scripts/gdb/linux/utils.py') diff --git a/scripts/gdb/linux/utils.py b/scripts/gdb/linux/utils.py index 03ebdccf5f69..877404e92dbb 100644 --- a/scripts/gdb/linux/utils.py +++ b/scripts/gdb/linux/utils.py @@ -200,7 +200,7 @@ def get_gdbserver_type(): def probe_kgdb(): try: - thread_info = gdb.execute("info thread 2", to_string=True) + thread_info = gdb.execute("info thread 1", to_string=True) return "shadowCPU" in thread_info except gdb.error: return False -- cgit v1.2.3 From 3545414f2590177a76f86c985130dc4824d3adc9 Mon Sep 17 00:00:00 2001 From: Ilya Leoshkevich Date: Thu, 15 May 2025 17:52:11 +0200 Subject: scripts/gdb/symbols: factor out get_vmlinux() Patch series "scripts/gdb/symbols: determine KASLR offset on s390 during early boot". I noticed that debugging s390 early boot using the support I introduced in commit 28939c3e9925 ("scripts/gdb/symbols: determine KASLR offset on s390") does not work. The reason is that decompressor does not provide the vmcoreinfo note, so KASLR offset needs to be extracted in a different way, which this series implements. Patches 1-2 are trivial refactorings, and patch 3 is the implementation. This patch (of 3): Move the code that determines the current vmlinux file into a separate function. It will be useful later in order to analyze the kernel image in physical memory during s390 early boot. Link: https://lkml.kernel.org/r/20250515155811.114392-1-iii@linux.ibm.com Link: https://lkml.kernel.org/r/20250515155811.114392-2-iii@linux.ibm.com Signed-off-by: Ilya Leoshkevich Cc: Alexander Gordeev Cc: Heiko Carstens Cc: Jan Kiszka Cc: Kieran Bingham Cc: Vasily Gorbik Signed-off-by: Andrew Morton --- scripts/gdb/linux/symbols.py | 6 +----- scripts/gdb/linux/utils.py | 9 +++++++++ 2 files changed, 10 insertions(+), 5 deletions(-) (limited to 'scripts/gdb/linux/utils.py') diff --git a/scripts/gdb/linux/symbols.py b/scripts/gdb/linux/symbols.py index b255177301e9..25c4627c60e5 100644 --- a/scripts/gdb/linux/symbols.py +++ b/scripts/gdb/linux/symbols.py @@ -178,11 +178,7 @@ lx-symbols command.""" saved_states.append({'breakpoint': bp, 'enabled': bp.enabled}) # drop all current symbols and reload vmlinux - orig_vmlinux = 'vmlinux' - for obj in gdb.objfiles(): - if (obj.filename.endswith('vmlinux') or - obj.filename.endswith('vmlinux.debug')): - orig_vmlinux = obj.filename + orig_vmlinux = utils.get_vmlinux() gdb.execute("symbol-file", to_string=True) kerneloffset = get_kerneloffset() if kerneloffset is None: diff --git a/scripts/gdb/linux/utils.py b/scripts/gdb/linux/utils.py index 877404e92dbb..6e125830d3f2 100644 --- a/scripts/gdb/linux/utils.py +++ b/scripts/gdb/linux/utils.py @@ -251,3 +251,12 @@ def parse_vmcore(s): else: kerneloffset = int(match.group(1), 16) return VmCore(kerneloffset=kerneloffset) + + +def get_vmlinux(): + vmlinux = 'vmlinux' + for obj in gdb.objfiles(): + if (obj.filename.endswith('vmlinux') or + obj.filename.endswith('vmlinux.debug')): + vmlinux = obj.filename + return vmlinux -- cgit v1.2.3 From e97c4a27cb9c4c06fdc6d0760d7ea031c98b58a5 Mon Sep 17 00:00:00 2001 From: Ilya Leoshkevich Date: Thu, 15 May 2025 17:52:12 +0200 Subject: scripts/gdb/symbols: factor out pagination_off() Move the code that turns off pagination into a separate function. It will be useful later in order to prevent hangs when loading symbols for kernel image in physical memory during s390 early boot. Link: https://lkml.kernel.org/r/20250515155811.114392-3-iii@linux.ibm.com Signed-off-by: Ilya Leoshkevich Cc: Alexander Gordeev Cc: Heiko Carstens Cc: Jan Kiszka Cc: Kieran Bingham Cc: Vasily Gorbik Signed-off-by: Andrew Morton --- scripts/gdb/linux/symbols.py | 20 +++++++------------- scripts/gdb/linux/utils.py | 11 +++++++++++ 2 files changed, 18 insertions(+), 13 deletions(-) (limited to 'scripts/gdb/linux/utils.py') diff --git a/scripts/gdb/linux/symbols.py b/scripts/gdb/linux/symbols.py index 25c4627c60e5..0c7af712c44c 100644 --- a/scripts/gdb/linux/symbols.py +++ b/scripts/gdb/linux/symbols.py @@ -38,19 +38,13 @@ if hasattr(gdb, 'Breakpoint'): # Disable pagination while reporting symbol (re-)loading. # The console input is blocked in this context so that we would # get stuck waiting for the user to acknowledge paged output. - show_pagination = gdb.execute("show pagination", to_string=True) - pagination = show_pagination.endswith("on.\n") - gdb.execute("set pagination off") - - if module_name in cmd.loaded_modules: - gdb.write("refreshing all symbols to reload module " - "'{0}'\n".format(module_name)) - cmd.load_all_symbols() - else: - cmd.load_module_symbols(module) - - # restore pagination state - gdb.execute("set pagination %s" % ("on" if pagination else "off")) + with utils.pagination_off(): + if module_name in cmd.loaded_modules: + gdb.write("refreshing all symbols to reload module " + "'{0}'\n".format(module_name)) + cmd.load_all_symbols() + else: + cmd.load_module_symbols(module) return False diff --git a/scripts/gdb/linux/utils.py b/scripts/gdb/linux/utils.py index 6e125830d3f2..e11f6f67961a 100644 --- a/scripts/gdb/linux/utils.py +++ b/scripts/gdb/linux/utils.py @@ -260,3 +260,14 @@ def get_vmlinux(): obj.filename.endswith('vmlinux.debug')): vmlinux = obj.filename return vmlinux + + +@contextlib.contextmanager +def pagination_off(): + show_pagination = gdb.execute("show pagination", to_string=True) + pagination = show_pagination.endswith("on.\n") + gdb.execute("set pagination off") + try: + yield + finally: + gdb.execute("set pagination %s" % ("on" if pagination else "off")) -- cgit v1.2.3