From 518049d9d3e25dcd7be6e3d728e86f292ad0c922 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (VMware)" Date: Fri, 10 May 2019 12:05:46 -0400 Subject: [PATCH] ftrace/x86_32: Remove support for non DYNAMIC_FTRACE 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) --- arch/x86/Kconfig | 11 +++++++++++ arch/x86/kernel/ftrace_32.S | 39 --------------------------------------- 2 files changed, 11 insertions(+), 39 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 5ad92419be19..0544041ae3a2 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -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 # diff --git a/arch/x86/kernel/ftrace_32.S b/arch/x86/kernel/ftrace_32.S index 4c8440de3355..459e6b4a19bc 100644 --- a/arch/x86/kernel/ftrace_32.S +++ b/arch/x86/kernel/ftrace_32.S @@ -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 3*4(%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) -- 2.11.0