csky: Add perf callchain support

This patch add support for perf callchain sampling on csky platform.
As fp is used to unwind the stack, the program being sampled and the
C library need to be compiled with -mbacktrace for user callchains,
kernel callchains require CONFIG_STACKTRACE = y.

Changelog:
 - Coding convention with Christoph's advice for riscv's.

Signed-off-by: Mao Han <han_mao@c-sky.com>
Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Cc: Christoph Hellwig <hch@infradead.org>

diff --git a/arch/csky/kernel/Makefile b/arch/csky/kernel/Makefile
index 484e6d3a364719b521c6586a4a06df9d57d12b82..4c462f584dd1a904a006083f75e73bcb6282cd8b 100644 (file)
--- a/arch/csky/kernel/Makefile
+++ b/arch/csky/kernel/Makefile
@@ -9,6 +9,7 @@ obj-$(CONFIG_SMP)                       += smp.o
 obj-$(CONFIG_FUNCTION_TRACER)          += ftrace.o
 obj-$(CONFIG_STACKTRACE)               += stacktrace.o
 obj-$(CONFIG_CSKY_PMU_V1)              += perf_event.o
+obj-$(CONFIG_PERF_EVENTS)              += perf_callchain.o
 
 ifdef CONFIG_FUNCTION_TRACER
 CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)

diff --git a/arch/csky/kernel/perf_callchain.c b/arch/csky/kernel/perf_callchain.c
new file mode 100644 (file)
index 0000000..e68ff37
--- /dev/null
+++ b/arch/csky/kernel/perf_callchain.c
@@ -0,0 +1,119 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2019 Hangzhou C-SKY Microsystems co.,ltd.
+
+#include <linux/perf_event.h>
+#include <linux/uaccess.h>
+
+/* Kernel callchain */
+struct stackframe {
+       unsigned long fp;
+       unsigned long lr;
+};
+
+static int unwind_frame_kernel(struct stackframe *frame)
+{
+       if (kstack_end((void *)frame->fp))
+               return -EPERM;
+       if (frame->fp & 0x3 || frame->fp < TASK_SIZE)
+               return -EPERM;
+
+       *frame = *(struct stackframe *)frame->fp;
+       if (__kernel_text_address(frame->lr)) {
+               int graph = 0;
+
+               frame->lr = ftrace_graph_ret_addr(NULL, &graph, frame->lr,
+                               NULL);
+       }
+       return 0;
+}
+
+static void notrace walk_stackframe(struct stackframe *fr,
+                       struct perf_callchain_entry_ctx *entry)
+{
+       do {
+               perf_callchain_store(entry, fr->lr);
+       } while (unwind_frame_kernel(fr) >= 0);
+}
+
+/*
+ * Get the return address for a single stackframe and return a pointer to the
+ * next frame tail.
+ */
+static unsigned long user_backtrace(struct perf_callchain_entry_ctx *entry,
+                       unsigned long fp, unsigned long reg_lr)
+{
+       struct stackframe buftail;
+       unsigned long lr = 0;
+       unsigned long *user_frame_tail = (unsigned long *)fp;
+
+       /* Check accessibility of one struct frame_tail beyond */
+       if (!access_ok(user_frame_tail, sizeof(buftail)))
+               return 0;
+       if (__copy_from_user_inatomic(&buftail, user_frame_tail,
+                                     sizeof(buftail)))
+               return 0;
+
+       if (reg_lr != 0)
+               lr = reg_lr;
+       else
+               lr = buftail.lr;
+
+       fp = buftail.fp;
+       perf_callchain_store(entry, lr);
+
+       return fp;
+}
+
+/*
+ * This will be called when the target is in user mode
+ * This function will only be called when we use
+ * "PERF_SAMPLE_CALLCHAIN" in
+ * kernel/events/core.c:perf_prepare_sample()
+ *
+ * How to trigger perf_callchain_[user/kernel] :
+ * $ perf record -e cpu-clock --call-graph fp ./program
+ * $ perf report --call-graph
+ *
+ * On C-SKY platform, the program being sampled and the C library
+ * need to be compiled with * -mbacktrace, otherwise the user
+ * stack will not contain function frame.
+ */
+void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
+                        struct pt_regs *regs)
+{
+       unsigned long fp = 0;
+
+       /* C-SKY does not support virtualization. */
+       if (perf_guest_cbs && perf_guest_cbs->is_in_guest())
+               return;
+
+       fp = regs->regs[4];
+       perf_callchain_store(entry, regs->pc);
+
+       /*
+        * While backtrace from leaf function, lr is normally
+        * not saved inside frame on C-SKY, so get lr from pt_regs
+        * at the sample point. However, lr value can be incorrect if
+        * lr is used as temp register
+        */
+       fp = user_backtrace(entry, fp, regs->lr);
+
+       while (fp && !(fp & 0x3) && entry->nr < entry->max_stack)
+               fp = user_backtrace(entry, fp, 0);
+}
+
+void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
+                          struct pt_regs *regs)
+{
+       struct stackframe fr;
+
+       /* C-SKY does not support virtualization. */
+       if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
+               pr_warn("C-SKY does not support perf in guest mode!");
+               return;
+       }
+
+       fr.fp = regs->regs[4];
+       fr.lr = regs->lr;
+       walk_stackframe(&fr, entry);
+}