Le 28/07/2016 à 13:57, Peter Maydell a écrit :
> For i386, the ABI specifies that 'long long' (8 byte values)
> need only be 4 aligned, but we were requiring them to be
> 8-aligned. This meant we were laying out the target_epoll_event
> structure wrongly. Add a suitable ifdef to abitypes.h to
> specify the i386-specific alignment requirement.
gdb qemu-i386
(gdb) p &(((struct target_epoll_event *)0)->data)
$1 = (target_epoll_data_t *) 0x8
whereas:
gdb qemu-x86_64
(gdb) p &(((struct target_epoll_event *)0)->data)
$1 = (target_epoll_data_t *) 0x4
I've checked on real systems x86_64/i386:
-----
#include <sys/epoll.h>
int main(void)
{
volatile struct epoll_event e;
e.events = 0;
}
----
(gdb) p &(((struct epoll_event *)0)->data)
$1 = (epoll_data_t *) 0x4
but on ppc64, I have
(gdb) p &(((struct epoll_event *)0)->data)
$1 = (epoll_data_t *) 0x8
In fact, the structure should be packed in both cases, something like:
--- a/linux-user/syscall_defs.h
+++ b/linux-user/syscall_defs.h
@@ -2562,7 +2562,7 @@ struct target_mq_attr {
#define FUTEX_CMD_MASK ~(FUTEX_PRIVATE_FLAG |
FUTEX_CLOCK_REALTIME)
#ifdef CONFIG_EPOLL
-#if defined(TARGET_X86_64)
+#if defined(TARGET_X86_64) || defined(TARGET_I386)
#define TARGET_EPOLL_PACKED QEMU_PACKED
#else
#define TARGET_EPOLL_PACKED
on my Fedora systems x86_64/i386:
/usr/include/bits/epoll.h
#define __EPOLL_PACKED __attribute__ ((__packed__))
/usr/include/sys/epoll.h
struct epoll_event
{
uint32_t events; /* Epoll events */
epoll_data_t data; /* User data variable */
} __EPOLL_PACKED;
but I don't understand why in linux source tree we have
#ifdef __x86_64__
#define EPOLL_PACKED __attribute__((packed))
#else
#define EPOLL_PACKED
#endif
struct epoll_event {
__u32 events;
__u64 data;
} EPOLL_PACKED;
Laurent
