From b29c62868f58af09b600118a394a0263bab5e52d Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Tue, 21 May 2019 21:16:15 -0400 Subject: [PATCH] Introduce callstack stackwalk implementation header Introduce a new implementation header for the stackwalk-based API, added in Linux 5.2 and gradually integrated within each architecture. Signed-off-by: Mathieu Desnoyers --- lttng-context-callstack-stackwalk-impl.h | 230 +++++++++++++++++++++++ lttng-context-callstack.c | 4 + 2 files changed, 234 insertions(+) create mode 100644 lttng-context-callstack-stackwalk-impl.h diff --git a/lttng-context-callstack-stackwalk-impl.h b/lttng-context-callstack-stackwalk-impl.h new file mode 100644 index 00000000..dfb60c55 --- /dev/null +++ b/lttng-context-callstack-stackwalk-impl.h @@ -0,0 +1,230 @@ +/* SPDX-License-Identifier: (GPL-2.0 or LGPL-2.1) + * + * lttng-context-callstack-stackwalk-impl.h + * + * LTTng callstack event context, stackwalk implementation. Targets + * kernels and architectures using the stacktrace common infrastructure + * introduced in the upstream Linux kernel by commit 214d8ca6ee + * "stacktrace: Provide common infrastructure" (merged in Linux 5.2, + * then gradually introduced within architectures). + * + * Copyright (C) 2014-2019 Mathieu Desnoyers + * Copyright (C) 2014 Francis Giraldeau + */ + +#define MAX_ENTRIES 128 + +enum lttng_cs_ctx_modes { + CALLSTACK_KERNEL = 0, + CALLSTACK_USER = 1, + NR_CALLSTACK_MODES, +}; + +struct lttng_stack_trace { + unsigned long entries[MAX_ENTRIES]; + unsigned int nr_entries; +}; + +struct lttng_cs { + struct lttng_stack_trace stack_trace[RING_BUFFER_MAX_NESTING]; +}; + +struct field_data { + struct lttng_cs __percpu *cs_percpu; + enum lttng_cs_ctx_modes mode; +}; + +static +unsigned int (*save_func_kernel)(unsigned long *store, unsigned int size, + unsigned int skipnr); +static +unsigned int (*save_func_user)(unsigned long *store, unsigned int size); + +static +const char *lttng_cs_ctx_mode_name(enum lttng_cs_ctx_modes mode) +{ + switch (mode) { + case CALLSTACK_KERNEL: + return "callstack_kernel"; + case CALLSTACK_USER: + return "callstack_user"; + default: + return NULL; + } +} + +static +int init_type_callstack_kernel(void) +{ + unsigned long func; + const char *func_name = "stack_trace_save"; + + if (save_func_kernel) + return 0; + func = kallsyms_lookup_funcptr(func_name); + if (!func) { + printk(KERN_WARNING "LTTng: symbol lookup failed: %s\n", + func_name); + return -EINVAL; + } + save_func_kernel = (void *) func; + return 0; +} + +static +int init_type_callstack_user(void) +{ + unsigned long func; + const char *func_name = "stack_trace_save_user"; + + if (save_func_user) + return 0; + func = kallsyms_lookup_funcptr(func_name); + if (!func) { + printk(KERN_WARNING "LTTng: symbol lookup failed: %s\n", + func_name); + return -EINVAL; + } + save_func_user = (void *) func; + return 0; +} + +static +int init_type(enum lttng_cs_ctx_modes mode) +{ + switch (mode) { + case CALLSTACK_KERNEL: + return init_type_callstack_kernel(); + case CALLSTACK_USER: + return init_type_callstack_user(); + default: + return -EINVAL; + } +} + +static +void lttng_cs_set_init(struct lttng_cs __percpu *cs_set) +{ +} + +/* Keep track of nesting inside userspace callstack context code */ +DEFINE_PER_CPU(int, callstack_user_nesting); + +static +struct lttng_stack_trace *stack_trace_context(struct lttng_ctx_field *field, + struct lib_ring_buffer_ctx *ctx) +{ + int buffer_nesting, cs_user_nesting; + struct lttng_cs *cs; + struct field_data *fdata = field->priv; + + /* + * Do not gather the userspace callstack context when the event was + * triggered by the userspace callstack context saving mechanism. + */ + cs_user_nesting = per_cpu(callstack_user_nesting, ctx->cpu); + + if (fdata->mode == CALLSTACK_USER && cs_user_nesting >= 1) + return NULL; + + /* + * get_cpu() is not required, preemption is already + * disabled while event is written. + * + * max nesting is checked in lib_ring_buffer_get_cpu(). + * Check it again as a safety net. + */ + cs = per_cpu_ptr(fdata->cs_percpu, ctx->cpu); + buffer_nesting = per_cpu(lib_ring_buffer_nesting, ctx->cpu) - 1; + if (buffer_nesting >= RING_BUFFER_MAX_NESTING) + return NULL; + + return &cs->stack_trace[buffer_nesting]; +} + +/* + * In order to reserve the correct size, the callstack is computed. The + * resulting callstack is saved to be accessed in the record step. + */ +static +size_t lttng_callstack_get_size(size_t offset, struct lttng_ctx_field *field, + struct lib_ring_buffer_ctx *ctx, + struct lttng_channel *chan) +{ + struct lttng_stack_trace *trace; + struct field_data *fdata = field->priv; + size_t orig_offset = offset; + + /* do not write data if no space is available */ + trace = stack_trace_context(field, ctx); + if (unlikely(!trace)) { + offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned int)); + offset += sizeof(unsigned int); + offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned long)); + return offset - orig_offset; + } + + /* reset stack trace, no need to clear memory */ + trace->nr_entries = 0; + + switch (fdata->mode) { + case CALLSTACK_KERNEL: + /* do the real work and reserve space */ + trace->nr_entries = save_func_kernel(trace->entries, + MAX_ENTRIES, 0); + break; + case CALLSTACK_USER: + ++per_cpu(callstack_user_nesting, ctx->cpu); + /* do the real work and reserve space */ + trace->nr_entries = save_func_user(trace->entries, + MAX_ENTRIES); + per_cpu(callstack_user_nesting, ctx->cpu)--; + break; + default: + WARN_ON_ONCE(1); + } + + /* + * If the array is filled, add our own marker to show that the + * stack is incomplete. + */ + offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned int)); + offset += sizeof(unsigned int); + offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned long)); + offset += sizeof(unsigned long) * trace->nr_entries; + /* Add our own ULONG_MAX delimiter to show incomplete stack. */ + if (trace->nr_entries == MAX_ENTRIES) + offset += sizeof(unsigned long); + return offset - orig_offset; +} + +static +void lttng_callstack_record(struct lttng_ctx_field *field, + struct lib_ring_buffer_ctx *ctx, + struct lttng_channel *chan) +{ + struct lttng_stack_trace *trace = stack_trace_context(field, ctx); + unsigned int nr_seq_entries; + + if (unlikely(!trace)) { + nr_seq_entries = 0; + lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned int)); + chan->ops->event_write(ctx, &nr_seq_entries, sizeof(unsigned int)); + lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned long)); + return; + } + lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned int)); + nr_seq_entries = trace->nr_entries; + if (trace->nr_entries == MAX_ENTRIES) + nr_seq_entries++; + chan->ops->event_write(ctx, &nr_seq_entries, sizeof(unsigned int)); + lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned long)); + chan->ops->event_write(ctx, trace->entries, + sizeof(unsigned long) * trace->nr_entries); + /* Add our own ULONG_MAX delimiter to show incomplete stack. */ + if (trace->nr_entries == MAX_ENTRIES) { + unsigned long delim = ULONG_MAX; + + chan->ops->event_write(ctx, &delim, sizeof(unsigned long)); + } +} diff --git a/lttng-context-callstack.c b/lttng-context-callstack.c index 4a440040..195990a6 100644 --- a/lttng-context-callstack.c +++ b/lttng-context-callstack.c @@ -49,7 +49,11 @@ #include "wrapper/vmalloc.h" #include "lttng-tracer.h" +#ifdef CONFIG_ARCH_STACKWALK +#include "lttng-context-callstack-stackwalk-impl.h" +#else #include "lttng-context-callstack-legacy-impl.h" +#endif static void field_data_free(struct field_data *fdata) -- 2.34.1