Messages in this thread Patch in this message | | | Date | Wed, 28 Oct 2020 09:15:43 -0400 | From | Steven Rostedt <> | Subject | [RFC][PATCH 1/2] ftrace/x86: Allow for arguments to be passed in to REGS by default |
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From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
Currently, the only way to get access to the registers of a function via a ftrace callback is to set the "FL_FLAGS" bit in the ftrace_ops. But as this saves all regs as if a breakpoint were to trigger (for use with kprobes), it is expensive.
The regs are already saved on the stack for the default ftrace callbacks, as that is required otherwise a function being traced will get the wrong arguments and possibly crash. And on x86, the argumentes are already stored where they would be on a pt_regs structure to use that code for both the regs version of a callback, it makes sense to pass that information always to all functions.
If an architecture does this (as x86 now does), it is to set HAVE_DYNAMIC_FTRACE_WITH_ARGS, and this will let the generic code that it could use the regs without having to set the flags if it wants to access the arguments from the regs pointer.
The stack pointer is also saved in the regs, and this could be useful for having the function graph tracer not require its own trampoline!
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> --- arch/x86/Kconfig | 1 + arch/x86/kernel/ftrace_64.S | 12 +++++++----- kernel/trace/Kconfig | 9 +++++++++ 3 files changed, 17 insertions(+), 5 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 7101ac64bb20..b4d2b1fcfd09 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -167,6 +167,7 @@ config X86 select HAVE_DMA_CONTIGUOUS select HAVE_DYNAMIC_FTRACE select HAVE_DYNAMIC_FTRACE_WITH_REGS + select HAVE_DYNAMIC_FTRACE_WITH_ARGS if X86_64 select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS select HAVE_EBPF_JIT select HAVE_EFFICIENT_UNALIGNED_ACCESS diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S index ac3d5f22fe64..77c512334b4c 100644 --- a/arch/x86/kernel/ftrace_64.S +++ b/arch/x86/kernel/ftrace_64.S @@ -86,6 +86,11 @@ movq %r8, R8(%rsp) movq %r9, R9(%rsp) movq $0, ORIG_RAX(%rsp) + + /* Stack - skipping return address and flags */ + leaq MCOUNT_REG_SIZE+\added+8(%rsp), %rcx + movq %rcx, RSP(%rsp) + /* * Save the original RBP. Even though the mcount ABI does not * require this, it helps out callers. @@ -144,8 +149,8 @@ SYM_INNER_LABEL(ftrace_caller_op_ptr, SYM_L_GLOBAL) /* Load the ftrace_ops into the 3rd parameter */ movq function_trace_op(%rip), %rdx - /* regs go into 4th parameter (but make it NULL) */ - movq $0, %rcx + /* regs go into 4th parameter */ + leaq (%rsp), %rcx SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) call ftrace_stub @@ -204,9 +209,6 @@ SYM_INNER_LABEL(ftrace_regs_caller_op_ptr, SYM_L_GLOBAL) movq %rcx, SS(%rsp) movq $__KERNEL_CS, %rcx movq %rcx, CS(%rsp) - /* Stack - skipping return address and flags */ - leaq MCOUNT_REG_SIZE+8*2(%rsp), %rcx - movq %rcx, RSP(%rsp) ENCODE_FRAME_POINTER diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index a4020c0b4508..6a5b7a818d7d 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -31,6 +31,15 @@ config HAVE_DYNAMIC_FTRACE_WITH_REGS config HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS bool +config HAVE_DYNAMIC_FTRACE_WITH_ARGS + bool + help + If this is set, then arguments and stack can be found from + the pt_regs passed into the function callback regs parameter + by default, even without setting the REGS flag in the ftrace_ops. + This allows for use of regs_get_kernel_argument() and + kernel_stack_pointer(). + config HAVE_FTRACE_MCOUNT_RECORD bool help -- 2.28.0
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