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Groups > linux.kernel > #1591545
| From | Arnd Bergmann <arnd@arndb.de> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings |
| Date | 2017-03-03 00:20 +0100 |
| Message-ID | <tgIaR-Qo-9@gated-at.bofh.it> (permalink) |
| References | (6 earlier) <tgdJM-4r7-19@gated-at.bofh.it> <tgemt-4Vt-9@gated-at.bofh.it> <tggeC-6gA-7@gated-at.bofh.it> <tgleh-1ix-9@gated-at.bofh.it> <tgnzr-34a-7@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Thu, Mar 2, 2017 at 2:03 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> On Wed, Mar 01, 2017 at 11:42:54PM +0100, Arnd Bergmann wrote:
>> On Wed, Mar 1, 2017 at 5:53 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>> > On Wed, Mar 01, 2017 at 04:27:29PM +0100, Arnd Bergmann wrote:
>>
>> > I see no apparent reason for the ud2.
>>
>> It's the possible division by zero. This change would avoid the ud2:
>>
>> diff --git a/drivers/i2c/busses/i2c-img-scb.c b/drivers/i2c/busses/i2c-img-scb.c
>> index db8e8b40569d..a2b09c518225 100644
>> --- a/drivers/i2c/busses/i2c-img-scb.c
>> +++ b/drivers/i2c/busses/i2c-img-scb.c
>> @@ -1196,6 +1196,8 @@ static int img_i2c_init(struct img_i2c *i2c)
>> clk_khz /= prescale;
>>
>> /* Setup the clock increment value */
>> + if (clk_khz < 1)
>> + clk_khz = 1;
>> inc = (256 * 16 * bitrate_khz) / clk_khz;
>>
>> /*
>
> Ok, I see what gcc is doing.
>
> clk_khz = clk_get_rate(i2c->scb_clk) / 1000;
> ...
> inc = (256 * 16 * bitrate_khz) / clk_khz;
>
> Because CONFIG_HAVE_CLK isn't set, clk_get_rate() returns 0, which means
> clk_khz is always zero, so the last statement *always* results in a
> divide-by-zero. So that looks like a bug in the code.
>
> However, I'm baffled by how gcc handles it. Instead of:
>
> a) reporting a compile-time warning/error; or
>
> b) letting the #DE (divide error) exception happen;
>
> it inserts a 'ud2', resulting in a #UD (invalid opcode). Why?!?
Just FYI, I found another one like this:
0000000000000000 <hibvt_pwm_get_state>:
0: e8 00 00 00 00 callq 5 <hibvt_pwm_get_state+0x5>
1: R_X86_64_PC32 __fentry__-0x4
5: 8b 46 10 mov 0x10(%rsi),%eax
8: 55 push %rbp
9: 48 89 e5 mov %rsp,%rbp
c: c1 e0 05 shl $0x5,%eax
f: 48 03 47 48 add 0x48(%rdi),%rax
13: 8b 00 mov (%rax),%eax
15: 0f 0b ud2
17: 66 0f 1f 84 00 00 00 nopw 0x0(%rax,%rax,1)
1e: 00 00
static inline unsigned long clk_get_rate(struct clk *clk)
{
return 0;
}
static void hibvt_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
struct pwm_state *state)
{
struct hibvt_pwm_chip *hi_pwm_chip = to_hibvt_pwm_chip(chip);
void __iomem *base;
u32 freq, value;
freq = div_u64(clk_get_rate(hi_pwm_chip->clk), 1000000);
base = hi_pwm_chip->base;
value = readl(base + PWM_CFG0_ADDR(pwm->hwpwm));
state->period = div_u64(value * 1000, freq);
value = readl(base + PWM_CFG1_ADDR(pwm->hwpwm));
state->duty_cycle = div_u64(value * 1000, freq);
value = readl(base + PWM_CTRL_ADDR(pwm->hwpwm));
state->enabled = (PWM_ENABLE_MASK & value);
}
Arnd
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Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Arnd Bergmann <arnd@arndb.de> - 2017-03-01 10:40 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Arnd Bergmann <arnd@arndb.de> - 2017-03-01 11:00 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-01 15:50 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-01 18:30 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Arnd Bergmann <arnd@arndb.de> - 2017-03-01 23:10 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Arnd Bergmann <arnd@arndb.de> - 2017-03-01 23:50 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-02 02:20 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Ingo Molnar <mingo@kernel.org> - 2017-03-02 07:40 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Ingo Molnar <mingo@kernel.org> - 2017-03-02 15:00 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-02 15:30 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Ingo Molnar <mingo@kernel.org> - 2017-03-02 15:50 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-02 15:10 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Arnd Bergmann <arnd@arndb.de> - 2017-03-03 00:20 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-03 01:00 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Arnd Bergmann <arnd@arndb.de> - 2017-03-03 10:30 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Arnd Bergmann <arnd@arndb.de> - 2017-03-03 16:40 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Arnd Bergmann <arnd@arndb.de> - 2017-03-01 16:30 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-02 19:40 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Arnd Bergmann <arnd@arndb.de> - 2017-03-03 00:00 +0100
Re: [PATCH] objtool: fix another gcc jump table detection issue Arnd Bergmann <arnd@arndb.de> - 2017-03-03 00:10 +0100
[PATCH] objtool: fix another gcc jump table detection issue Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-03 04:20 +0100
Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-01 16:30 +0100
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