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ftrace/x86_32: Remove support for non DYNAMIC_FTRACE

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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>
This commit is contained in:
Steven Rostedt (VMware) 2019-05-10 12:05:46 -04:00
parent a15fd609ad
commit 518049d9d3
2 changed files with 11 additions and 39 deletions
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11
arch/x86/Kconfig
View File

@ -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
#

39
arch/x86/kernel/ftrace_32.S
View File

@ -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)