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arm-none-eabi-gcc default parameters

mastupristi

how to know exactly which parameters are enabled/disabled by default for arm-none-eabi-gcc?

I have the doubt thinking about the parameter `-fshort-enum`.

Try to compile this example (main.c):

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#include <stdio.h>
typedef enum
{
A,
B,
C,
max_e,
} e_t;
/* static assert for detect size of e_t @compile time using DIM symbol */
_Static_assert(DIM == sizeof(e_t), "sizeof do not match");
void f(e_t p)
{
if(p<0 || p>=max_e){
printf("out of range %d\n", p);
return;
}
printf("p %d\n", p);
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

First I used gcc on my ubuntu 18.04 (with '-DDIM=x -std=gnu11 -Wall -Wextra' parameters):

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max@resfw04:~/progs/test_enum_signed$ gcc --version
gcc (Ubuntu 7.4.0-1ubuntu1~18.04.1) 7.4.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
max@resfw04:~/progs/test_enum_signed$ gcc -DDIM=1 -std=gnu11 -Wall -Wextra main.c -c -o main.o
main.c:12:1: error: static assertion failed: "sizeof do not match"
max@resfw04:~/progs/test_enum_signed$ gcc -DDIM=2 -std=gnu11 -Wall -Wextra main.c -c -o main.o
main.c:12:1: error: static assertion failed: "sizeof do not match"
max@resfw04:~/progs/test_enum_signed$ gcc -DDIM=4 -std=gnu11 -Wall -Wextra main.c -c -o main.o
max@resfw04:~/progs/test_enum_signed$
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

As you can see I have gcc 7.4.0 on my machine, and it seems that the default is '-fno-short-enum', in fact the build fails with DIM other than 4.

The I tried to compile with arm toolchain (same parameters):

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max@resfw04:~/progs/test_enum_signed$ arm-none-eabi-gcc --version
arm-none-eabi-gcc (GNU Tools for Arm Embedded Processors 7-2018-q2-update) 7.3.1 20180622 (release) [ARM/embedded-7-branch revision 261907]
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
max@resfw04:~/progs/test_enum_signed$ arm-none-eabi-gcc -DDIM=1 -std=gnu11 -Wall -Wextra main.c -c -o main.o
main.c: In function 'f':
main.c:16:6: warning: comparison is always false due to limited range of data type [-Wtype-limits]
if(p<0 || p>=max_e){
^
max@resfw04:~/progs/test_enum_signed$ arm-none-eabi-gcc -DDIM=2 -std=gnu11 -Wall -Wextra main.c -c -o main.o
main.c:12:1: error: static assertion failed: "sizeof do not match"
_Static_assert(DIM == sizeof(e_t), "sizeof do not match");
^~~~~~~~~~~~~~
main.c: In function 'f':
main.c:16:6: warning: comparison is always false due to limited range of data type [-Wtype-limits]
if(p<0 || p>=max_e){
^
max@resfw04:~/progs/test_enum_signed$ arm-none-eabi-gcc -DDIM=4 -std=gnu11 -Wall -Wextra main.c -c -o main.o
main.c:12:1: error: static assertion failed: "sizeof do not match"
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

In this case it seems that is enabled '-fshort-enum' by default, in fact the build fails with DIM other than 1, and I have also a warning.

So I must deduce that the default of the two gcc's is different, I guess for other parameters, maybe even many.

Where can I find the default parameters for arm-none-eabi-gcc? Is it a document distributed with the toolchain or online? Or should I look at the sources? And in the latter case exactly where?

best regards

Max

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