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GCC allows specifying declaration attributes using the keyword __attribute__((__packed__)). When this attribute is present, the compiler will not add padding bytes for memory alignment unless an unless an explicit alignment specifier for a structure member requires the introduction of padding bytes.
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#include <stddef.h>
struct test {
int a;
char b;
int c;
} __attribute__((__packed__));
/* Safely copy bytes to user space */
extern int copy_to_user(void *dest, void *src, size_t size);
void do_stuff(void *usr_buf) {
struct test arg = {.a = 1, .b = 2, .c = 3};
copy_to_user(usr_buf, &arg, sizeof(arg));
}
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