Does not build for strict C99

[miniwinwm]

If compiler option -std=c99 is added the build fails because of some inline assembly instructions. While this is not a major problem, some projects require it.

[kilograham]

Helpful if you give build output; also how you chose to add -std=c99

[miniwinwm]

In my project I added the -std=c99 compiler flag in CMakeCache.txt, after running cmake, like this...

//Flags used by the C compiler during all build types.
CMAKE_C_FLAGS:STRING=-mcpu=cortex-m0plus -mthumb -std=c99

This line...

#include "pico/stdlib.h"

eventually includes platform.h, and it's this code that causes the error...

inline static int32_t __mul_instruction(int32_t a, int32_t b) {
asm ("mul %0, %1" : "+l" (a) : "l" (b) : );
return a;

The errors are first it thinks asm is a function and complains about an implicit declaration, then it barfs on the : in the middle as it's not C.

I have tried reproducing it using the standard examples, for example blink.c. I made the same change to pico-examples/build/CMakeCache.txt, but the blink project built without error so somehow the -std=c99 compiler flags I made is not getting transmitted through the examples build process.

My cmake file is unremarkable...

cmake_minimum_required(VERSION 3.12)
include(pico_sdk_import.cmake)
project(MiniWinSimple)
pico_sdk_init()

add_compile_definitions(RASPBERRY_PI_PICO)

include_directories(
...
)

add_executable(MiniWinSimple
...
)

target_link_libraries(MiniWinSimple pico_stdlib hardware_spi hardware_flash)

pico_add_extra_outputs(MiniWinSimple)

If it helps, the project I tried it on is here...

https://github.com/miniwinwm/miniwinwm/tree/master/RaspberryPi/Pico/MiniWinSimple

[kilograham]

Does it work with __asm instead of asm?

[miniwinwm]

It gets through the asm problem, but then fails on static_assert in address_mapped.h. I think typeof in sem.c is going to be a problem as well. It looks like that one needs to be __typeof.

[kilograham]

Note the best way to specify C99 is to do

project(MiniWinSimple C ASM)
set(CMAKE_C_STANDARD 99)

which will do --std=gnu99 which gets use the asm/typeof stuff. You can add the follow

#ifndef static_assert
#define static_assert _Static_Assert
#endif

for now. you can edit a header, or inject it via the PICO_CONFIG_HEADER_FILES variable:

list(APPEND PICO_CONFIG_HEADER_FILES path/to/foo.h)

and it will be included in all files.

[kilograham]

note that we don't claim to work with C99, however if the changes needed for support arer non invasive we will fix them individually

[miniwinwm]

Thanks for your input. I shall work through the problems to see if I can make progress and if it's only trivial changes needed to get it to work I'll add them here.

[Wirtos]

C99 has no static assert, but one might use typedef trick to create one if there's no compiler-specific way

#define concat_(a, b) a##b
#define concat(a, b) concat_(a, b)
#define static_assert(cond, message) typedef char assertion_on_line_##__LINE__[(cond) ? 1 : -1]

static_assert(0, "message"); <- compilation error here

[DwayneGit]

I am running into this problem now with trying to compile.

error: expected declaration specifiers or '...' before string constant
  106 |     static_assert( NUM_TIMERS == 4, "");

if i comment it out all good.

any thoughts to adding a check to all the static_asserts:

#if __STDC_VERSION__ >= 201112L
    static_assert( NUM_TIMERS == 4, "");
#endif

or piggy backing off of @Wirtos adding something like this to pico/assert.h:

#if __STDC_VERSION__ < 201112L
  #define concat_(a, b) a##b
  #define concat(a, b) concat_(a, b)
  #define static_assert(cond, message) typedef char assertion_on_line_##__LINE__[(cond) ? 1 : -1]
#endif

[Wirtos]

I am running into this problem now with trying to compile.

error: expected declaration specifiers or '...' before string constant
  106 |     static_assert( NUM_TIMERS == 4, "");

if i comment it out all good.

any thoughts to adding a check to all the static_asserts:

#if __STDC_VERSION__ >= 201112L
    static_assert( NUM_TIMERS == 4, "");
#endif

or piggy backing off of @Wirtos adding something like this to pico/assert.h:

#if __STDC_VERSION__ >= 201112L
  #define concat_(a, b) a##b
  #define concat(a, b) concat_(a, b)
  #define static_assert(cond, message) typedef char assertion_on_line_##__LINE__[(cond) ? 1 : -1]
#endif

Whoops, that one had a little mistake with concat being unused. Indeed this solution should work in most of the use-cases except static asserts declared inside structs or unions, also could add compiler-specific flags to silence unused warnings about declared typedefs

#define concat_(a, b) a##b
#define concat(a, b) concat_(a, b)
#define static_assert(cond, message) typedef char concat(assertion_on_line_, __LINE__)[(cond) ? 1 : -1]