https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93873
Bug ID: 93873
Summary: gcc or lto-wrapper does not consider individual
bitfield values on static analysis and instead tests
the whole value of all bitfield bits combined
Product: gcc
Version: 6.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: emil.fihlman at aalto dot fi
Target Milestone: ---
On gcc version 6.3.0 20170516 (Debian 6.3.0-18+deb9u1)
Given these two files (and stdtypes.h being available from
https://emil.fi/d/stdtypes.h but it's basically just include stdint.h and
typedef u?int\d+_t to the correct [su]\d+
$cat ltobuglib.h
#include <stdtypes.h>
#include <stdlib.h>
#include <unistd.h>
struct thing
{
u64 v;
struct
{
u64 dox:1;
u64 freeme:1;
} flags;
};
struct thing *makeit(struct thing *t)
{
u8 dynamic=!t;
if(dynamic)
{
t=calloc(1, sizeof(*t));
if(!t)
{
return(NULL);
}
}
t->v=0;
t->flags.dox=1;
t->flags.freeme=dynamic;
return(t);
}
void freeit(struct thing *t)
{
if(t->flags.freeme)
{
free(t);
}
}
$cat ltobug.c
#include <stdtypes.h>
#include <stdio.h>
#include "ltobuglib.h"
s32 main(void)
{
struct thing t={0};
if(!makeit(&t))
{
return(-1);
}
printf("%lu %u %u\n", t.v, t.flags.dox, t.flags.freeme);
freeit(&t);
return(0);
}
$gcc -Wall -Werror -Wextra -O3 -flto -o ltobug ltobug.c
produces
In function ‘freeit’,
inlined from ‘main’ at ltobug.c:13:2:
ltobuglib.h:36:3: error: attempt to free a non-heap object ‘t’
[-Werror=free-nonheap-object]
free(t);
^
lto1: all warnings being treated as errors
lto-wrapper: fatal error: gcc returned 1 exit status
compilation terminated.
/usr/bin/ld: error: lto-wrapper failed
collect2: error: ld returned 1 exit status
but changing t->flags.dox=1 to 0 compiles cleanly.
Without -flto (and dox set to 1) the result is
In file included from ltobug.c:3:0:
In function ‘freeit’,
inlined from ‘main’ at ltobug.c:13:2:
ltobuglib.h:36:3: error: attempt to free a non-heap object ‘t’
[-Werror=free-nonheap-object]
free(t);
^~~~~~~
cc1: all warnings being treated as errors
On a different project of mine, the code cleanly compiles without -flto (but
fails with -flto as above) but here gcc seems to do the same issue without
-flto, too.
