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* [Bug c/40394] New: Variable values calculated differently depending on storage class
@ 2009-06-10 10:39 goran dot steen at enea dot com
2009-06-10 12:42 ` [Bug c/40394] " goran dot steen at enea dot com
` (8 more replies)
0 siblings, 9 replies; 10+ messages in thread
From: goran dot steen at enea dot com @ 2009-06-10 10:39 UTC (permalink / raw)
To: gcc-bugs
/************* CODE EXAMPLE ***************/
#include <stdio.h>
#include <string.h>
typedef unsigned int U32;
typedef unsigned short U16;
typedef unsigned char U8;
#ifndef __GNUC__
#define __attribute__(a)
#endif /* __GNUC__ */
#define APP6DR_PACK_STRUCT __attribute__((packed))
#define APP6DR_INLINE_FUNC(func) \
__inline__ func __attribute__((always_inline)); \
extern __inline__ __attribute__((gnu_inline)) func
struct app6drIpHdr
{
unsigned int ip_v :4;
unsigned int ip_hl :4;
U8 ip_tos;
U16 ip_len;
U16 ip_id;
U16 ip_off;
U8 ip_ttl;
U8 ip_p;
U16 ip_sum;
struct
{
U32 ip_sa;
U32 ip_da;
} ip_addr_r;
} APP6DR_PACK_STRUCT;
typedef struct app6drIpHdr App6drIpHdr;
#define APP6DR_CALC_CSUM(hdr_p,len,cs) App6dr_calcCs16((const char*)(hdr_p),
(len), &(cs))
APP6DR_INLINE_FUNC(void App6dr_calcCs16(const char* hdr_p,
U32 len,
volatile U16* cs_p))
{
U32 i, sum;
for(i=0, sum=0; i<(len)/2; i++)
{
U32 val = ((U32*)hdr_p)[i];
sum += ((val&0xffff) + (val>>16));
}
if ((len) & 1) sum += ((U16*)hdr_p)[(len)-1];
while(sum>>16) sum = (sum&0xffff)+(sum>>16);
*cs_p = (U16)(~sum);
}
#define APP6DR_CALC_IPV4_CSUM(ipv4_p) \
(ipv4_p)->ip_sum = 0x0000; \
APP6DR_CALC_CSUM((char*)(ipv4_p),sizeof(App6drIpHdr)/2,(ipv4_p)->ip_sum)
#define DOIT() \
memset((void*)&iph, 0xfe, sizeof(App6drIpHdr)); \
iph.ip_v = 4; \
iph.ip_hl = 5; \
iph.ip_tos = 0; \
iph.ip_len = 0; \
iph.ip_id = 0; \
iph.ip_off = 0; \
iph.ip_ttl = 64; /* XXX */ \
iph.ip_p = 50; /* ESP */ \
iph.ip_addr_r.ip_sa = (U32) sa; \
iph.ip_addr_r.ip_da = (U32) da; \
APP6DR_CALC_IPV4_CSUM(&iph);\
fprintf(stderr, "checksum = 0x%04x\n", iph.ip_sum);
void testchksum2(U32 sa, U32 da)
{
static App6drIpHdr iph;
DOIT();
}
void testchksum1(U32 sa, U32 da)
{
App6drIpHdr iph;
DOIT();
}
int main()
{
testchksum1(0x0a0a0a14, 0x0a0a0a01);
testchksum2(0x0a0a0a14, 0x0a0a0a01);
return 0;
}
/************ END OF CODE EXAMPLE **************/
Compiled with
gcc -Os -Wall -pedantic main.c -o runme
Output:
checksum = 0xa89c
checksum = 0xa542
The only difference between outputs are that the variables made calculations on
have different storage classes, ie automatic and static.
--
Summary: Variable values calculated differently depending on
storage class
Product: gcc
Version: 4.2.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: goran dot steen at enea dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40394
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug c/40394] Variable values calculated differently depending on storage class
2009-06-10 10:39 [Bug c/40394] New: Variable values calculated differently depending on storage class goran dot steen at enea dot com
2009-06-10 12:42 ` [Bug c/40394] " goran dot steen at enea dot com
@ 2009-06-10 12:42 ` goran dot steen at enea dot com
2009-06-10 12:43 ` goran dot steen at enea dot com
` (6 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: goran dot steen at enea dot com @ 2009-06-10 12:42 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from goran dot steen at enea dot com 2009-06-10 12:42 -------
*** Bug 40396 has been marked as a duplicate of this bug. ***
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40394
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug c/40394] Variable values calculated differently depending on storage class
2009-06-10 10:39 [Bug c/40394] New: Variable values calculated differently depending on storage class goran dot steen at enea dot com
@ 2009-06-10 12:42 ` goran dot steen at enea dot com
2009-06-10 12:42 ` goran dot steen at enea dot com
` (7 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: goran dot steen at enea dot com @ 2009-06-10 12:42 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from goran dot steen at enea dot com 2009-06-10 12:42 -------
*** Bug 40395 has been marked as a duplicate of this bug. ***
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40394
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug c/40394] Variable values calculated differently depending on storage class
2009-06-10 10:39 [Bug c/40394] New: Variable values calculated differently depending on storage class goran dot steen at enea dot com
` (3 preceding siblings ...)
2009-06-10 12:43 ` goran dot steen at enea dot com
@ 2009-06-10 12:43 ` goran dot steen at enea dot com
2009-06-10 12:44 ` goran dot steen at enea dot com
` (3 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: goran dot steen at enea dot com @ 2009-06-10 12:43 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from goran dot steen at enea dot com 2009-06-10 12:43 -------
*** Bug 40399 has been marked as a duplicate of this bug. ***
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40394
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug c/40394] Variable values calculated differently depending on storage class
2009-06-10 10:39 [Bug c/40394] New: Variable values calculated differently depending on storage class goran dot steen at enea dot com
` (2 preceding siblings ...)
2009-06-10 12:43 ` goran dot steen at enea dot com
@ 2009-06-10 12:43 ` goran dot steen at enea dot com
2009-06-10 12:43 ` goran dot steen at enea dot com
` (4 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: goran dot steen at enea dot com @ 2009-06-10 12:43 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from goran dot steen at enea dot com 2009-06-10 12:43 -------
*** Bug 40398 has been marked as a duplicate of this bug. ***
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40394
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug c/40394] Variable values calculated differently depending on storage class
2009-06-10 10:39 [Bug c/40394] New: Variable values calculated differently depending on storage class goran dot steen at enea dot com
2009-06-10 12:42 ` [Bug c/40394] " goran dot steen at enea dot com
2009-06-10 12:42 ` goran dot steen at enea dot com
@ 2009-06-10 12:43 ` goran dot steen at enea dot com
2009-06-10 12:43 ` goran dot steen at enea dot com
` (5 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: goran dot steen at enea dot com @ 2009-06-10 12:43 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from goran dot steen at enea dot com 2009-06-10 12:42 -------
*** Bug 40397 has been marked as a duplicate of this bug. ***
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40394
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug c/40394] Variable values calculated differently depending on storage class
2009-06-10 10:39 [Bug c/40394] New: Variable values calculated differently depending on storage class goran dot steen at enea dot com
` (4 preceding siblings ...)
2009-06-10 12:43 ` goran dot steen at enea dot com
@ 2009-06-10 12:44 ` goran dot steen at enea dot com
2009-06-10 14:03 ` rguenth at gcc dot gnu dot org
` (2 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: goran dot steen at enea dot com @ 2009-06-10 12:44 UTC (permalink / raw)
To: gcc-bugs
------- Comment #6 from goran dot steen at enea dot com 2009-06-10 12:43 -------
*** Bug 40400 has been marked as a duplicate of this bug. ***
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40394
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug c/40394] Variable values calculated differently depending on storage class
2009-06-10 10:39 [Bug c/40394] New: Variable values calculated differently depending on storage class goran dot steen at enea dot com
` (5 preceding siblings ...)
2009-06-10 12:44 ` goran dot steen at enea dot com
@ 2009-06-10 14:03 ` rguenth at gcc dot gnu dot org
2009-06-12 6:20 ` goran dot steen at enea dot com
2009-06-12 6:57 ` pinskia at gcc dot gnu dot org
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2009-06-10 14:03 UTC (permalink / raw)
To: gcc-bugs
------- Comment #7 from rguenth at gcc dot gnu dot org 2009-06-10 14:02 -------
You are violating C aliasing rules. Use -fno-strict-aliasing.
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40394
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug c/40394] Variable values calculated differently depending on storage class
2009-06-10 10:39 [Bug c/40394] New: Variable values calculated differently depending on storage class goran dot steen at enea dot com
` (6 preceding siblings ...)
2009-06-10 14:03 ` rguenth at gcc dot gnu dot org
@ 2009-06-12 6:20 ` goran dot steen at enea dot com
2009-06-12 6:57 ` pinskia at gcc dot gnu dot org
8 siblings, 0 replies; 10+ messages in thread
From: goran dot steen at enea dot com @ 2009-06-12 6:20 UTC (permalink / raw)
To: gcc-bugs
------- Comment #8 from goran dot steen at enea dot com 2009-06-12 06:20 -------
Since -pedantic was given as compiler option, gcc should have warned about
violating C aliasing rules.
--
goran dot steen at enea dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |goran dot steen at enea dot
| |com
Status|RESOLVED |UNCONFIRMED
Resolution|INVALID |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40394
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug c/40394] Variable values calculated differently depending on storage class
2009-06-10 10:39 [Bug c/40394] New: Variable values calculated differently depending on storage class goran dot steen at enea dot com
` (7 preceding siblings ...)
2009-06-12 6:20 ` goran dot steen at enea dot com
@ 2009-06-12 6:57 ` pinskia at gcc dot gnu dot org
8 siblings, 0 replies; 10+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2009-06-12 6:57 UTC (permalink / raw)
To: gcc-bugs
------- Comment #9 from pinskia at gcc dot gnu dot org 2009-06-12 06:57 -------
Not all aliasing violations can be detected by the compiler :).
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40394
^ permalink raw reply [flat|nested] 10+ messages in thread
end of thread, other threads:[~2009-06-12 6:57 UTC | newest]
Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
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2009-06-10 10:39 [Bug c/40394] New: Variable values calculated differently depending on storage class goran dot steen at enea dot com
2009-06-10 12:42 ` [Bug c/40394] " goran dot steen at enea dot com
2009-06-10 12:42 ` goran dot steen at enea dot com
2009-06-10 12:43 ` goran dot steen at enea dot com
2009-06-10 12:43 ` goran dot steen at enea dot com
2009-06-10 12:43 ` goran dot steen at enea dot com
2009-06-10 12:44 ` goran dot steen at enea dot com
2009-06-10 14:03 ` rguenth at gcc dot gnu dot org
2009-06-12 6:20 ` goran dot steen at enea dot com
2009-06-12 6:57 ` pinskia at gcc dot gnu dot org
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