Hello! I've got a problem because I don't understand what this message means:

In file included from /usr/src/linux/include/linux/spinlock.h:6,
from /usr/src/linux/include/linux/module.h:12,
from driver/modules/hostap_cs.c:8:
/usr/src/linux/include/asm/system.h: In function `__set_64bit_var':
/usr/src/linux/include/asm/system.h:190: warning: dereferencing type-punned pointer will break strict-aliasing rules
/usr/src/linux/include/asm/system.h:190: warning: dereferencing type-punned pointer will break strict-aliasing rules

Could anyone help me?thank you very much! lucs

Albeit annoying, I don't think these warnings are very serious. Does the build fail? What exactly is it you're compiling?

looks like he's compiling a kernel; those warnings are just warnings. Errors are what you need to worry about

In fact...these aren't errors and the system compiles the file but I would like to know: why these warnings appear? And how can I read these lines?For example....what is the file that cause warning?

the red is the file that gcc is complaining about

the blue is the line number where the error/warning occurs

I've noticed this and other oddities since I started using 10.1.

from the gcc manual:

-fstrict-aliasing
Allows the compiler to assume the strictest aliasing rules applicable to the language being compiled. For C (and C++), this activates optimizations based on the type of expressions. In particular, an object of one type is assumed never to reside at the same address as an object of a different type, unless the types are almost the same. For example, an unsigned int can alias an int, but not a void* or a double. A character type may alias any other type.

Pay special attention to code like this:

union a_union {
int i;
double d;
};

int f() {
a_union t;
t.d = 3.0;
return t.i;
}


The practice of reading from a different union member than the one most recently written to (called “type-punning”) is common. Even with -fstrict-aliasing, type-punning is allowed, provided the memory is accessed through the union type. So, the code above will work as expected. However, this code might not:

int f() {
a_union t;
int* ip;
t.d = 3.0;
ip = &t.i;
return *ip;
}


Every language that wishes to perform language-specific alias analysis should define a function that computes, given an tree node, an alias set for the node. Nodes in different alias sets are not allowed to alias. For an example, see the C front-end function c_get_alias_set.

Enabled at levels -O2, -O3, -Os.

keep in mind it also depends on the version of gcc being used. a recent version is going to spit out more warnings than an older version due to depecated features and such.