http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56997
Bug #: 56997
Summary: Incorrect write to packed field when
strict-volatile-bitfields enabled on aarch32
Classification: Unclassified
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: joey...@arm.com
Target: arm/aarch32
Attached case fails when
Target: all arm aarch32
Optimization level:all optimization levels.
Version: Trunk 197955, 4.7, 4.6
But it passes:
- if -fno-strict-volatile-bitfields is specified, or
- on x86 even if -fstrict-volatile-bitfields is specified
For example:
arm-none-eabi-gcc -mthumb -mcpu=cortex-m0 -Os a.c -o a.s -S
foo:
ldr r3, .L2
lsl r2, r0, #8 ; First byte of input r0 is truncated
ldr r0, [r3]
uxtb r0, r0
orr r0, r2
str r0, [r3]
bx lr
Runtime output:
Write FAIL 0x20304
---------------------
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#ifdef SHORT
#define test_type unsigned short
#define MAGIC 0x102u
#else
#define test_type unsigned int
#define MAGIC 0x1020304u
#endif
typedef struct s{
unsigned char Prefix;
test_type Type;
}__attribute((__packed__)) ss;
volatile ss v;
ss g;
void __attribute__((noinline))
foo (test_type u)
{
v.Type = u;
}
test_type __attribute__((noinline))
bar (void)
{
return v.Type;
}
int main()
{
test_type temp;
int err = 0;
foo(MAGIC);
memcpy(&g, (void *)&v, sizeof(g));
if (g.Type != MAGIC)
{
printf("Write FAIL 0x%x\n", g.Type);
err ++;
}
g.Type = MAGIC;
memcpy((void *)&v, &g, sizeof(v));
temp = bar();
if (temp != MAGIC)
{
printf("Read FAIL 0x%x\n", temp);
err ++;
}
return err;
}
