无法在MAKO中初始化ftrace

Question

I am trying to use ftrace in MAKO (Nexus 4)

With android-msm-mako-3.4-lollipop-release branch from msm.git, I just added below configuration in mako_defconfig

CONFIG_TRACING=y
CONFIG_FUNCTION_TRACER=y
CONFIG_DYNAMIC_FTRACE=y
CONFIG_STACK_TRACER=y
CONFIG_FUNCTION_GRAPH_TRACER=y

However, ftrace_init is failed in booting time There are some failed logs in kmsg

<6>[    0.002197] ftrace: allocating 32821 entries in 97 pages
<4>[    0.033053] ------------[ cut here ]------------
<4>[    0.033084] WARNING: at kernel/trace/ftrace.c:1590 ftrace_bug+0xec/0x174()
<4>[    0.033114] [<c0015230>] (unwind_backtrace+0x0/0xec) from [<c08a7dc4>] (dump_stack+0x20/0x24)
<4>[    0.033145] [<c08a7dc4>] (dump_stack+0x20/0x24) from [<c0075c98>] (warn_slowpath_common+0x58/0x70)
<4>[    0.033175] [<c0075c98>] (warn_slowpath_common+0x58/0x70) from [<c0075da8>] (warn_slowpath_null+0x2c/0x34)
<4>[    0.033206] [<c0075da8>] (warn_slowpath_null+0x2c/0x34) from [<c00e0558>] (ftrace_bug+0xec/0x174)
<4>[    0.033236] [<c00e0558>] (ftrace_bug+0xec/0x174) from [<c0d14a50>] (ftrace_init+0x408/0x4bc)
<4>[    0.033267] [<c0d14a50>] (ftrace_init+0x408/0x4bc) from [<c0d0095c>] (start_kernel+0x420/0x48c)
<4>[    0.033297] [<c0d0095c>] (start_kernel+0x420/0x48c) from [<8020803c>] (0x8020803c)
<4>[    0.033358] ---[ end trace d633338057b77c0d ]---
<6>[    0.033358] ftrace faulted on writing [<c010203c>] perf_output_put_handle+0x10/0xec

I think it can not write over 0xC010_0000, so it is a matter of kernel size But, I just added those trace configuration with vanila code, How can I fix this?

add some logs, I blocked ftrace_bug function, it calls ftrace_kill, it disable ftrace. Instead, I logged which function got a fault

<6>[    0.002350] ftrace: allocating 32821 entries in 97 pages
<4>[    0.032778] ftrace failed 2[<c010206c>] perf_output_put_handle+0x10/0xec
<4>[    0.032809] ftrace failed 2[<c057fd00>] iw_get_linkspeed+0x14/0x13c
<4>[    0.032839] ftrace failed 2[<c0886308>] wireless_spy_update+0x10/0xec

It looks like some specific functions are blocked to write;;

Answer 1

I found myself.

The reason was the write protection for kernel code area.

If you want to use ftrace in Nexus, you have to disable CONFIG_STRICT_MEMORY_RWX configuration in defconfig file.

I wish this can help you.