ftrace/x86_32: Remove support for non DYNAMIC_FTRACE (518049d9) · Commits · 戴 / test

When DYNAMIC_FTRACE is enabled in the kernel, all the functions that can be traced by the function tracer have a "nop" placeholder at the start of the function. When function tracing is enabled, the nop is converted into a call to the tracing infrastructure where the functions get traced. This also allows for specifying specific functions to trace, and a lot of infrastructure is built on top of this. When DYNAMIC_FTRACE is not enabled, all the functions have a call to the ftrace trampoline. A check is made to see if a function pointer is the ftrace_stub or not, and if it is not, it calls the function pointer to trace the code. This adds over 10% overhead to the kernel even when tracing is disabled. When an architecture supports DYNAMIC_FTRACE there really is no reason to use the static tracing. I have kept non DYNAMIC_FTRACE available in x86 so that the generic code for non DYNAMIC_FTRACE can be tested. There is no reason to support non DYNAMIC_FTRACE for both x86_64 and x86_32. As the non DYNAMIC_FTRACE for x86_32 does not even support fentry, and we want to remove mcount completely, there's no reason to keep non DYNAMIC_FTRACE around for x86_32. Signed-off-by:

Steven Rostedt (VMware) <rostedt@goodmis.org>

arch/x86/Kconfig

+11 −0

Original line number	Diff line number	Diff line
		@@ -31,6 +31,17 @@ config X86_64
		select X86_DEV_DMA_OPS
		select ARCH_HAS_SYSCALL_WRAPPER

		config FORCE_DYNAMIC_FTRACE
		def_bool y
		depends on X86_32
		depends on FUNCTION_TRACER
		select DYNAMIC_FTRACE
		help
		We keep the static function tracing (!DYNAMIC_FTRACE) around
		in order to test the non static function tracing in the
		generic code, as other architectures still use it. But we
		only need to keep it around for x86_64. No need to keep it
		for x86_32. For x86_32, force DYNAMIC_FTRACE.
		#
		# Arch settings
		#

arch/x86/kernel/ftrace_32.S

+0 −39

Original line number	Diff line number	Diff line
		@@ -18,8 +18,6 @@ EXPORT_SYMBOL(__fentry__)
		EXPORT_SYMBOL(mcount)
		#endif

		#ifdef CONFIG_DYNAMIC_FTRACE

		/* mcount uses a frame pointer even if CONFIG_FRAME_POINTER is not set */
		#if !defined(CC_USING_FENTRY) \|\| defined(CONFIG_FRAME_POINTER)
		# define USING_FRAME_POINTER
		@@ -170,43 +168,6 @@ GLOBAL(ftrace_regs_call)
		lea 34(%esp), %esp / Skip orig_ax, ip and cs */

		jmp .Lftrace_ret
		#else /* ! CONFIG_DYNAMIC_FTRACE */

		ENTRY(function_hook)
		cmpl $__PAGE_OFFSET, %esp
		jb ftrace_stub /* Paging not enabled yet? */

		cmpl $ftrace_stub, ftrace_trace_function
		jnz .Ltrace
		#ifdef CONFIG_FUNCTION_GRAPH_TRACER
		cmpl $ftrace_stub, ftrace_graph_return
		jnz ftrace_graph_caller

		cmpl $ftrace_graph_entry_stub, ftrace_graph_entry
		jnz ftrace_graph_caller
		#endif
		.globl ftrace_stub
		ftrace_stub:
		ret

		/* taken from glibc */
		.Ltrace:
		pushl %eax
		pushl %ecx
		pushl %edx
		movl 0xc(%esp), %eax
		movl 0x4(%ebp), %edx
		subl $MCOUNT_INSN_SIZE, %eax

		movl ftrace_trace_function, %ecx
		CALL_NOSPEC %ecx

		popl %edx
		popl %ecx
		popl %eax
		jmp ftrace_stub
		END(function_hook)
		#endif /* CONFIG_DYNAMIC_FTRACE */

		#ifdef CONFIG_FUNCTION_GRAPH_TRACER
		ENTRY(ftrace_graph_caller)

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