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DaggyStyle
Watchman
Joined: 22 Mar 2006
Posts: 5909
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 Posted: Wed Aug 21, 2019 5:27 am Post subject: handling undefined reference with lto |
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Greetings,
I've stumbled on this topic: https://stackoverflow.com/questions/4156585/how-to-get-the-length-of-a-function-in-bytes, I took the second example and tried it with lto enabled, when I compile it I get undefined reference to vars, see:
| Code: |
$ cat test.c
#include <stdio.h>
int i;
__attribute__((noinline, section(".mysection"))) void test_func (void)
{
i++;
}
int main (void)
{
extern unsigned char mysec_start[];
extern unsigned char mysec_end[];
printf ("Func len: %lu\n", mysec_end - mysec_start);
test_func ();
return 0;
}
$ gcc-7.3.0 -flto test.c -o test -DUSING_LTO
/tmp/ccSaKQu6.ltrans0.ltrans.o: In function `main':
<artificial>:(.text+0x5): undefined reference to `mysec_end'
<artificial>:(.text+0xa): undefined reference to `mysec_start'
collect2: error: ld returned 1 exit status |
any idea how to make it compile?
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Only two things are infinite, the universe and human stupidity and I'm not sure about the former - Albert Einstein |
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DaggyStyle
Watchman
Joined: 22 Mar 2006
Posts: 5909
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| Posted: Wed Aug 21, 2019 6:07 pm Post subject: |
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after looking into the thread, this seems to work:
| Code: |
#include <stdio.h>
int i;
__attribute__((noinline, section("mysection"))) void test_func (void)
{
i++;
}
int main (void)
{
extern unsigned char __start_mysection[];
extern unsigned char __stop_mysection[];
printf ("Func len: %lu\n", __stop_mysection - __start_mysection);
test_func ();
return 0;
} |
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Only two things are infinite, the universe and human stupidity and I'm not sure about the former - Albert Einstein |
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