Warning spi.c in function 'spi_tostring'

[Livius90]

Hi!

There are some "directive" warning in the spi.c.
Can you fix it to keep the "clean-coding"?

c-periphery/src/spi.c: In function 'spi_tostring':
c-periphery/src/spi.c:300:65: warning: '%u' directive output may be truncated writing between 1 and 3 bytes into a region of size 2 [-Wformat-truncation=]
         snprintf(bits_per_word_str, sizeof(bits_per_word_str), "%u", bits_per_word);
                                                                 ^~
c-periphery/src/spi.c:300:64: note: directive argument in the range [0, 255]
         snprintf(bits_per_word_str, sizeof(bits_per_word_str), "%u", bits_per_word);
                                                                ^~~~
c-periphery/src/spi.c:300:9: note: 'snprintf' output between 2 and 4 bytes into a destination of size 2
         snprintf(bits_per_word_str, sizeof(bits_per_word_str), "%u", bits_per_word);
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[vsergeev]

That's a pretty smart compiler to know it's not a problem with mode_str. I think the two choices for silencing this are either masking off bits_per_word in spi_get_bits_per_word() or increasing the size of bits_per_word_str to 4. Increasing the size is probably the better way.

[vsergeev]

Actually I do see the mode_str truncation warning, along with others:

src/pwm.c: In function ‘pwm_tostring’:
src/pwm.c:424:51: warning: ‘%f’ directive output may be truncated writing between 3 and 317 bytes into a region of size 16 [-Wformat-truncation=]
  424 |         snprintf(period_str, sizeof(period_str), "%f", period);
      |                                                   ^~
src/pwm.c:424:50: note: assuming directive output of 8 bytes
  424 |         snprintf(period_str, sizeof(period_str), "%f", period);
      |                                                  ^~~~
src/pwm.c:424:9: note: ‘snprintf’ output between 4 and 318 bytes into a destination of size 16
  424 |         snprintf(period_str, sizeof(period_str), "%f", period);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/pwm.c:429:59: warning: ‘%f’ directive output may be truncated writing between 3 and 317 bytes into a region of size 16 [-Wformat-truncation=]
  429 |         snprintf(duty_cycle_str, sizeof(duty_cycle_str), "%f", duty_cycle);
      |                                                           ^~
src/pwm.c:429:58: note: assuming directive output of 8 bytes
  429 |         snprintf(duty_cycle_str, sizeof(duty_cycle_str), "%f", duty_cycle);
      |                                                          ^~~~
src/pwm.c:429:9: note: ‘snprintf’ output between 4 and 318 bytes into a destination of size 16
  429 |         snprintf(duty_cycle_str, sizeof(duty_cycle_str), "%f", duty_cycle);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc -std=gnu99 -pedantic -Wall -Wextra -Wno-unused-parameter  -fPIC -Wformat-truncation=2 -DPERIPHERY_VERSION_COMMIT=\"v2.2.3-dirty\" -DPERIPHERY_GPIO_CDEV_SUPPORT=1  -c src/spi.c -o obj/spi.o
src/spi.c: In function ‘spi_tostring’:
src/spi.c:285:47: warning: ‘%u’ directive output may be truncated writing between 1 and 10 bytes into a region of size 2 [-Wformat-truncation=]
  285 |         snprintf(mode_str, sizeof(mode_str), "%u", mode);
      |                                               ^~
src/spi.c:285:9: note: ‘snprintf’ output between 2 and 11 bytes into a destination of size 2
  285 |         snprintf(mode_str, sizeof(mode_str), "%u", mode);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/spi.c:300:65: warning: ‘%u’ directive output may be truncated writing between 1 and 3 bytes into a region of size 2 [-Wformat-truncation=]
  300 |         snprintf(bits_per_word_str, sizeof(bits_per_word_str), "%u", bits_per_word);
      |                                                                 ^~
src/spi.c:300:9: note: ‘snprintf’ output between 2 and 4 bytes into a destination of size 2
  300 |         snprintf(bits_per_word_str, sizeof(bits_per_word_str), "%u", bits_per_word);
      |         ^~~~~~~~~

It doesn't make much sense to address the mode_str, period_str, duty_cycle_str warnings, since we're relying on truncation for the period and duty cycle floating point values, and we know know the mode is limited to values of 0 to 3 by the mask in spi_get_mode(). There's no memory safety concerns, since snprintf() will limit the total number of bytes written to the sizeof().

The bits_per_word one is a legitimate bug, so I've gone ahead and fixed that and included it in the v2.2.3 release.

[Livius90]

Thanks for fixing, now it builds well in new release.