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Date:   Sat, 15 Jan 2022 13:36:04 -0700
From:   Nathan Chancellor <nathan@kernel.org>
To:     Steven Rostedt <rostedt@goodmis.org>,
        Yinan Liu <yinan@linux.alibaba.com>
Cc:     linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        kernel test robot <lkp@intel.com>,
        kernel test robot <oliver.sang@intel.com>,
        llvm@lists.linux.dev
Subject: Re: [for-next][PATCH 10/31] scripts: ftrace - move the
 sort-processing in ftrace_init
Message-ID: <YeMwNEfNaGErFthk@archlinux-ax161>
References: <20220111173030.999527342@goodmis.org>
 <20220111173115.079437896@goodmis.org>
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In-Reply-To: <20220111173115.079437896@goodmis.org>
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Hi Steven and Yinan,

On Tue, Jan 11, 2022 at 12:30:41PM -0500, Steven Rostedt wrote:
> From: Yinan Liu <yinan@linux.alibaba.com>
> 
> When the kernel starts, the initialization of ftrace takes
> up a portion of the time (approximately 6~8ms) to sort mcount
> addresses. We can save this time by moving mcount-sorting to
> compile time.
> 
> Link: https://lkml.kernel.org/r/20211212113358.34208-2-yinan@linux.alibaba.com
> 
> Signed-off-by: Yinan Liu <yinan@linux.alibaba.com>
> Reported-by: kernel test robot <lkp@intel.com>
> Reported-by: kernel test robot <oliver.sang@intel.com>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

This change as commit 72b3942a173c ("scripts: ftrace - move the
sort-processing in ftrace_init") in -next causes a bunch of warnings at
the beginning of the build when using clang as the host compiler:

$ make -skj"$(nproc)" LLVM=1 distclean allmodconfig init/main.o
In file included from scripts/sorttable.c:195:
scripts/sorttable.h:380:6: warning: variable 'mcount_sort_thread' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
        if (!mstruct.init_data_sec || !_start_mcount_loc || !_stop_mcount_loc) {
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:479:6: note: uninitialized use occurs here
        if (mcount_sort_thread) {
            ^~~~~~~~~~~~~~~~~~
scripts/sorttable.h:380:2: note: remove the 'if' if its condition is always false
        if (!mstruct.init_data_sec || !_start_mcount_loc || !_stop_mcount_loc) {
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:380:6: warning: variable 'mcount_sort_thread' is used uninitialized whenever '||' condition is true [-Wsometimes-uninitialized]
        if (!mstruct.init_data_sec || !_start_mcount_loc || !_stop_mcount_loc) {
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:479:6: note: uninitialized use occurs here
        if (mcount_sort_thread) {
            ^~~~~~~~~~~~~~~~~~
scripts/sorttable.h:380:6: note: remove the '||' if its condition is always false
        if (!mstruct.init_data_sec || !_start_mcount_loc || !_stop_mcount_loc) {
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:380:6: warning: variable 'mcount_sort_thread' is used uninitialized whenever '||' condition is true [-Wsometimes-uninitialized]
        if (!mstruct.init_data_sec || !_start_mcount_loc || !_stop_mcount_loc) {
            ^~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:479:6: note: uninitialized use occurs here
        if (mcount_sort_thread) {
            ^~~~~~~~~~~~~~~~~~
scripts/sorttable.h:380:6: note: remove the '||' if its condition is always false
        if (!mstruct.init_data_sec || !_start_mcount_loc || !_stop_mcount_loc) {
            ^~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:288:30: note: initialize the variable 'mcount_sort_thread' to silence this warning
        pthread_t mcount_sort_thread;
                                    ^
                                     = 0
In file included from scripts/sorttable.c:197:
scripts/sorttable.h:380:6: warning: variable 'mcount_sort_thread' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
        if (!mstruct.init_data_sec || !_start_mcount_loc || !_stop_mcount_loc) {
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:479:6: note: uninitialized use occurs here
        if (mcount_sort_thread) {
            ^~~~~~~~~~~~~~~~~~
scripts/sorttable.h:380:2: note: remove the 'if' if its condition is always false
        if (!mstruct.init_data_sec || !_start_mcount_loc || !_stop_mcount_loc) {
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:380:6: warning: variable 'mcount_sort_thread' is used uninitialized whenever '||' condition is true [-Wsometimes-uninitialized]
        if (!mstruct.init_data_sec || !_start_mcount_loc || !_stop_mcount_loc) {
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:479:6: note: uninitialized use occurs here
        if (mcount_sort_thread) {
            ^~~~~~~~~~~~~~~~~~
scripts/sorttable.h:380:6: note: remove the '||' if its condition is always false
        if (!mstruct.init_data_sec || !_start_mcount_loc || !_stop_mcount_loc) {
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:380:6: warning: variable 'mcount_sort_thread' is used uninitialized whenever '||' condition is true [-Wsometimes-uninitialized]
        if (!mstruct.init_data_sec || !_start_mcount_loc || !_stop_mcount_loc) {
            ^~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:479:6: note: uninitialized use occurs here
        if (mcount_sort_thread) {
            ^~~~~~~~~~~~~~~~~~
scripts/sorttable.h:380:6: note: remove the '||' if its condition is always false
        if (!mstruct.init_data_sec || !_start_mcount_loc || !_stop_mcount_loc) {
            ^~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:370:6: warning: variable 'mcount_sort_thread' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
        if (pthread_create(&orc_sort_thread, NULL,
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:479:6: note: uninitialized use occurs here
        if (mcount_sort_thread) {
            ^~~~~~~~~~~~~~~~~~
scripts/sorttable.h:370:2: note: remove the 'if' if its condition is always false
        if (pthread_create(&orc_sort_thread, NULL,
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:360:6: warning: variable 'mcount_sort_thread' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
        if (orc_ip_size % sizeof(int) != 0 ||
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:479:6: note: uninitialized use occurs here
        if (mcount_sort_thread) {
            ^~~~~~~~~~~~~~~~~~
scripts/sorttable.h:360:2: note: remove the 'if' if its condition is always false
        if (orc_ip_size % sizeof(int) != 0 ||
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:360:6: warning: variable 'mcount_sort_thread' is used uninitialized whenever '||' condition is true [-Wsometimes-uninitialized]
        if (orc_ip_size % sizeof(int) != 0 ||
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:479:6: note: uninitialized use occurs here
        if (mcount_sort_thread) {
            ^~~~~~~~~~~~~~~~~~
scripts/sorttable.h:360:6: note: remove the '||' if its condition is always false
        if (orc_ip_size % sizeof(int) != 0 ||
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:360:6: warning: variable 'mcount_sort_thread' is used uninitialized whenever '||' condition is true [-Wsometimes-uninitialized]
        if (orc_ip_size % sizeof(int) != 0 ||
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:479:6: note: uninitialized use occurs here
        if (mcount_sort_thread) {
            ^~~~~~~~~~~~~~~~~~
scripts/sorttable.h:360:6: note: remove the '||' if its condition is always false
        if (orc_ip_size % sizeof(int) != 0 ||
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:353:6: warning: variable 'mcount_sort_thread' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
        if (!g_orc_ip_table || !g_orc_table) {
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:479:6: note: uninitialized use occurs here
        if (mcount_sort_thread) {
            ^~~~~~~~~~~~~~~~~~
scripts/sorttable.h:353:2: note: remove the 'if' if its condition is always false
        if (!g_orc_ip_table || !g_orc_table) {
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
scripts/sorttable.h:353:6: warning: variable 'mcount_sort_thread' is used uninitialized whenever '||' condition is true [-Wsometimes-uninitialized]
        if (!g_orc_ip_table || !g_orc_table) {
            ^~~~~~~~~~~~~~~
scripts/sorttable.h:479:6: note: uninitialized use occurs here
        if (mcount_sort_thread) {
            ^~~~~~~~~~~~~~~~~~
scripts/sorttable.h:353:6: note: remove the '||' if its condition is always false
        if (!g_orc_ip_table || !g_orc_table) {
            ^~~~~~~~~~~~~~~~~~
scripts/sorttable.h:288:30: note: initialize the variable 'mcount_sort_thread' to silence this warning
        pthread_t mcount_sort_thread;
                                    ^
                                     = 0
12 warnings generated.

Should mcount_sort_thread be zero initialized or is there something else
going on here? I am currently hunting down a bunch of other regressions
so apologies for just the report rather than a patch to fix it.

Cheers,
Nathan