On 04/19/2017 03:28 PM, Russell King - ARM Linux wrote:
On Wed, Apr 19, 2017 at 12:03:58PM +0530, Srinivas Ramana wrote:
Hi,
While understanding how the alignment are handled on arm and arm64, we came
across the fixups for LDM/LDRD/STM on arm where as these fixups are not
present on arm64.
There may be some specific reason why these fixups are not ported to arm64.
Can you please help us understand this?
With this difference in how kernel handles 32-bit apps on arm and arm64,
there can be apps which are working without abort on arm, but fail on arm64
(SIGBUS). We have tried to get some history on web, but not successful.
If this is indeed missing on arm64, do you see any issue if its ported (does
it fail any guidance)?
Do you have an application that fails because of this? Your email makes
it sound very theoretical.
I don't have any application with me right now. But i just tried passing
an intentional misaligned address in a test program. When i say
intentional, please note this code is buggy and should be fixed.
So, my question is when arm has such fixups to handle such cases and do
gracefully, is there any reason why those fixups are not ported to
arm64? Again, I do agree that apps has to fix these instances, but we do
have fixups in arch/arm.
I do see that the compiler can detect (if its not intentionally induced)
such cases and avoiding to generate LDM/STM and generates multiple
LDR/STR. So, I just want to know if it is safe to assume that the
compiler would take care of all such misaligned addresses passed to LDM/STM?
------------------------>8---------------------------------------
struct locat {
int a;
int b;
int c;
int d;
};
int test_func()
{
struct locat *int_pool1;
struct locat int_pool2;
struct locat *int_pool3;
char *ptr;
int_pool1 = malloc(sizeof(struct locat) + 16);
ptr = (char *)int_pool1;
int_pool3 = (struct locat *)(ptr+1);
printf("pool1 addr: 0x%08x pool3 addr: 0x%08x \n", &int_pool1,
int_pool3);
int_pool2 = *int_pool3;
}
------------------------8<---------------------------------------
Thanks,
-- Srinivas R
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