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Message-ID: <0d37f1a0-7045-130c-9d01-7d26625acab4@windriver.com>
Date: Fri, 28 Jul 2023 13:39:02 +0800
From: Xiangyu Chen <xiangyu.chen@....windriver.com>
To: Jiri Olsa <olsajiri@...il.com>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] libbpf: fix warnings "'pad_type' 'pad_bits' 'new_off' may
be used uninitialized"
On 7/27/23 19:01, Jiri Olsa wrote:
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> On Thu, Jul 27, 2023 at 04:25:36PM +0800, Xiangyu Chen wrote:
>> From: Xiangyu Chen <xiangyu.chen@...driver.com>
>>
>> When turn on the yocto DEBUG_BUILD flag, the build options for gcc would enable maybe-uninitialized,
>> and following warnings would be reported as below:
> curious, what's the gcc version? I can't reproduce that,
Indeed, it's also strange to me, the compiler using gcc-11.3.0 which is
generated by yocto 4.2.2(mickledore branch).
The warning happens on turn on DEBUG_BUILD flag in yocto configuration,
but when disable the DEBUG_BUILD flag, this
warning disappeared.
I have compared w/wo the DEBUG_BUILD's kernel build parameters this
morning, when enabled the flag, the kernel build
parameters as normal, the warning won't happen. When I enabled the
DEBUG_BUILD, the cflags with -Og -g -feliminate-unused-debug-types
seems the debug cflags caused the false warning behavior.
> and we already have all warnings enabled:
>
> CFLAGS += -Werror -Wall
>
> they seem like false warnings also, because ARRAY_SIZE(pads)
> will be always > 0
>
> jirka
>
>> | btf_dump.c: In function 'btf_dump_emit_bit_padding':
>> | btf_dump.c:916:4: error: 'pad_type' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>> | 916 | btf_dump_printf(d, "\n%s%s: %d;", pfx(lvl), pad_type,
>> | | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> | 917 | in_bitfield ? new_off - cur_off : 0);
>> | | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> | btf_dump.c:929:6: error: 'pad_bits' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>> | 929 | if (bits == pad_bits) {
>> | | ^
>> | btf_dump.c:913:28: error: 'new_off' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>> | 913 | (new_off == next_off && roundup(cur_off, next_align * 8) != new_off) ||
>> | | ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> | HOSTLD scripts/mod/modpost
>>
>> Signed-off-by: Xiangyu Chen <xiangyu.chen@...driver.com>
>> ---
>> tools/lib/bpf/btf_dump.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
>> index 4d9f30bf7f01..79923c3b8777 100644
>> --- a/tools/lib/bpf/btf_dump.c
>> +++ b/tools/lib/bpf/btf_dump.c
>> @@ -867,8 +867,8 @@ static void btf_dump_emit_bit_padding(const struct btf_dump *d,
>> } pads[] = {
>> {"long", d->ptr_sz * 8}, {"int", 32}, {"short", 16}, {"char", 8}
>> };
>> - int new_off, pad_bits, bits, i;
>> - const char *pad_type;
>> + int new_off = 0, pad_bits = 0, bits, i;
>> + const char *pad_type = NULL;
>>
>> if (cur_off >= next_off)
>> return; /* no gap */
>> --
>> 2.34.1
>>
>>
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