Messages in this thread | | | Date | Sat, 23 Apr 2005 11:52:48 +0200 (MEST) | From | Mikael Pettersson <> | Subject | gcc-4.0.0 final miscompiles net/ipv4/devinet.c:devinet_sysctl_register() |
| |
gcc-4.0.0 miscompiles a pointer subtraction operation in net/ipv4/devinet.c, resulting in oopses from /sbin/sysctl.
Below is a copy of the test case I just sent to gcc bugzilla.
/Mikael
/* gcc4pointersubtractionbug.c * Written by Mikael Pettersson, mikpe@csd.uu.se, 2005-04-23. * * This program illustrates a code optimisation bug in * gcc-4.0.0 (final) and gcc-4.0.0-20050417, where a pointer * subtraction operation is compiled as a pointer addition. * Observed at -O2. gcc was configured for i686-pc-linux-gnu. * * This bug broke net/ipv4/devinet.c:devinet_sysctl_register() * in the linux-2.6.12-rc2 Linux kernel, causing /sbin/sysctl * to trigger kernel oopses. * * gcc-4.0.0-20050416 and earlier prereleases do not have this bug. */ #include <stdio.h> #include <string.h>
#define NRVARS 5
struct ipv4_devconf { int var[NRVARS]; }; struct ipv4_devconf ipv4_devconf[2];
struct ctl_table { void *data; };
struct devinet_sysctl_table { struct ctl_table devinet_vars[NRVARS]; };
void devinet_sysctl_relocate(struct devinet_sysctl_table *t, struct ipv4_devconf *p) { int i;
for (i = 0; i < NRVARS; i++) /* Initially data points to a field in ipv4_devconf[0]. This code relocates it to the corresponding field in *p. At -O2, gcc-4.0.0-20050417 and gcc-4.0.0 (final) miscompile this pointer subtraction as a pointer addition. */ t->devinet_vars[i].data += (char *)p - (char *)&ipv4_devconf[0]; }
struct devinet_sysctl_table devinet_sysctl;
int main(void) { struct devinet_sysctl_table t; int i;
for(i = 0; i < NRVARS; i++) devinet_sysctl.devinet_vars[i].data = &ipv4_devconf[0].var[i];
memcpy(&t, &devinet_sysctl, sizeof t); devinet_sysctl_relocate(&t, &ipv4_devconf[1]);
for(i = 0; i < NRVARS; i++) if (t.devinet_vars[i].data != &ipv4_devconf[1].var[i]) { fprintf(stderr, "t.devinet_vars[%u].data == %p, should be %p\n", i, t.devinet_vars[i].data, &ipv4_devconf[1].var[i]); return 1; }
printf("all ok\n"); return 0; } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |