Merge tag 'trace-v4.21' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing updates from Steven Rostedt:

 - Rework of the kprobe/uprobe and synthetic events to consolidate all
   the dynamic event code. This will make changes in the future easier.

 - Partial rewrite of the function graph tracing infrastructure. This
   will allow for multiple users of hooking onto functions to get the
   callback (return) of the function. This is the ground work for having
   kprobes and function graph tracer using one code base.

 - Clean up of the histogram code that will facilitate adding more
   features to the histograms in the future.

 - Addition of str_has_prefix() and a few use cases. There currently is
   a similar function strstart() that is used in a few places, but only
   returns a bool and not a length. These instances will be removed in
   the future to use str_has_prefix() instead.

 - A few other various clean ups as well.

* tag 'trace-v4.21' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: (57 commits)
  tracing: Use the return of str_has_prefix() to remove open coded numbers
  tracing: Have the historgram use the result of str_has_prefix() for len of prefix
  tracing: Use str_has_prefix() instead of using fixed sizes
  tracing: Use str_has_prefix() helper for histogram code
  string.h: Add str_has_prefix() helper function
  tracing: Make function ‘ftrace_exports’ static
  tracing: Simplify printf'ing in seq_print_sym
  tracing: Avoid -Wformat-nonliteral warning
  tracing: Merge seq_print_sym_short() and seq_print_sym_offset()
  tracing: Add hist trigger comments for variable-related fields
  tracing: Remove hist trigger synth_var_refs
  tracing: Use hist trigger's var_ref array to destroy var_refs
  tracing: Remove open-coding of hist trigger var_ref management
  tracing: Use var_refs[] for hist trigger reference checking
  tracing: Change strlen to sizeof for hist trigger static strings
  tracing: Remove unnecessary hist trigger struct field
  tracing: Fix ftrace_graph_get_ret_stack() to use task and not current
  seq_buf: Use size_t for len in seq_buf_puts()
  seq_buf: Make seq_buf_puts() null-terminate the buffer
  arm64: Use ftrace_graph_get_ret_stack() instead of curr_ret_stack
  ...

2 files changed, 26 insertions, 23 deletions

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 7ee8067cbf45..8257a59704ae 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -733,18 +733,20 @@ union ftrace_op_code_union {
 	} __attribute__((packed));
 };
 
+#define RET_SIZE		1
+
 static unsigned long
 create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 {
-	unsigned const char *jmp;
 	unsigned long start_offset;
 	unsigned long end_offset;
 	unsigned long op_offset;
 	unsigned long offset;
 	unsigned long size;
-	unsigned long ip;
+	unsigned long retq;
 	unsigned long *ptr;
 	void *trampoline;
+	void *ip;
 	/* 48 8b 15 <offset> is movq <offset>(%rip), %rdx */
 	unsigned const char op_ref[] = { 0x48, 0x8b, 0x15 };
 	union ftrace_op_code_union op_ptr;
@@ -764,27 +766,27 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 
 	/*
 	 * Allocate enough size to store the ftrace_caller code,
-	 * the jmp to ftrace_epilogue, as well as the address of
-	 * the ftrace_ops this trampoline is used for.
+	 * the iret , as well as the address of the ftrace_ops this
+	 * trampoline is used for.
 	 */
-	trampoline = alloc_tramp(size + MCOUNT_INSN_SIZE + sizeof(void *));
+	trampoline = alloc_tramp(size + RET_SIZE + sizeof(void *));
 	if (!trampoline)
 		return 0;
 
-	*tramp_size = size + MCOUNT_INSN_SIZE + sizeof(void *);
+	*tramp_size = size + RET_SIZE + sizeof(void *);
 
 	/* Copy ftrace_caller onto the trampoline memory */
 	ret = probe_kernel_read(trampoline, (void *)start_offset, size);
-	if (WARN_ON(ret < 0)) {
-		tramp_free(trampoline, *tramp_size);
-		return 0;
-	}
+	if (WARN_ON(ret < 0))
+		goto fail;
 
-	ip = (unsigned long)trampoline + size;
+	ip = trampoline + size;
 
-	/* The trampoline ends with a jmp to ftrace_epilogue */
-	jmp = ftrace_jmp_replace(ip, (unsigned long)ftrace_epilogue);
-	memcpy(trampoline + size, jmp, MCOUNT_INSN_SIZE);
+	/* The trampoline ends with ret(q) */
+	retq = (unsigned long)ftrace_stub;
+	ret = probe_kernel_read(ip, (void *)retq, RET_SIZE);
+	if (WARN_ON(ret < 0))
+		goto fail;
 
 	/*
 	 * The address of the ftrace_ops that is used for this trampoline
@@ -794,17 +796,15 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 	 * the global function_trace_op variable.
 	 */
 
-	ptr = (unsigned long *)(trampoline + size + MCOUNT_INSN_SIZE);
+	ptr = (unsigned long *)(trampoline + size + RET_SIZE);
 	*ptr = (unsigned long)ops;
 
 	op_offset -= start_offset;
 	memcpy(&op_ptr, trampoline + op_offset, OP_REF_SIZE);
 
 	/* Are we pointing to the reference? */
-	if (WARN_ON(memcmp(op_ptr.op, op_ref, 3) != 0)) {
-		tramp_free(trampoline, *tramp_size);
-		return 0;
-	}
+	if (WARN_ON(memcmp(op_ptr.op, op_ref, 3) != 0))
+		goto fail;
 
 	/* Load the contents of ptr into the callback parameter */
 	offset = (unsigned long)ptr;
@@ -819,6 +819,9 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 	ops->flags |= FTRACE_OPS_FL_ALLOC_TRAMP;
 
 	return (unsigned long)trampoline;
+fail:
+	tramp_free(trampoline, *tramp_size);
+	return 0;
 }
 
 static unsigned long calc_trampoline_call_offset(bool save_regs)
diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 91b2cff4b79a..75f2b36b41a6 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -171,9 +171,6 @@ GLOBAL(ftrace_call)
 	restore_mcount_regs
 
 	/*
-	 * The copied trampoline must call ftrace_epilogue as it
-	 * still may need to call the function graph tracer.
-	 *
 	 * The code up to this label is copied into trampolines so
 	 * think twice before adding any new code or changing the
 	 * layout here.
@@ -185,7 +182,10 @@ GLOBAL(ftrace_graph_call)
 	jmp ftrace_stub
 #endif
 
-/* This is weak to keep gas from relaxing the jumps */
+/*
+ * This is weak to keep gas from relaxing the jumps.
+ * It is also used to copy the retq for trampolines.
+ */
 WEAK(ftrace_stub)
 	retq
 ENDPROC(ftrace_caller)