Re: [Qemu-devel] [PATCH 1/2] linux-user: Define target alignment size
On Sun, Feb 13, 2011 at 4:22 AM, Laurent Vivier laur...@vivier.eu wrote:
Datatype alignment can be found using following application:
int main(void)
{
printf(alignof(short) %ld\n, __alignof__(short));
printf(alignof(int) %ld\n, __alignof__(int));
printf(alignof(long) %ld\n, __alignof__(long));
printf(alignof(long long) %ld\n, __alignof__(long long));
}
This patch includes following alignments:
i386
alignof(short) 2
alignof(int) 4
alignof(long) 4
alignof(long long) 8
x86_64
alignof(short) 2
alignof(int) 4
alignof(long) 8
alignof(long long) 8
arm
alignof(short) 2
alignof(int) 4
alignof(long) 4
alignof(long long) 4
m68k (680x0)
alignof(short) 2
alignof(int) 2
alignof(long) 2
alignof(long long) 2
mips
alignof(short) 2
alignof(int) 4
alignof(long) 4
alignof(long long) 8
ppc
alignof(short) 2
alignof(int) 4
alignof(long) 4
alignof(long long) 8
for other targets, use by default (2,4,4,8).
Please, update for your favorite target...
For Sparc32 (I think also sparc32plus), the default is OK.
For Sparc64, please use 2, 4, 8, 8. I'd guess other 64 bit platforms
(Alpha, MIPS64, PPC64 etc) should use the same.
Does GCC produce correct code using the attributes on strictly aligned
host, when the target is less strictly aligned?
Should the alignment of floating point variables be specified as well?
The strict alignment required for doubles is 4, but recommended
alignment is 8, I'm not sure which one is used for structures
containing doubles.
Re: [Qemu-devel] [PATCH 1/2] linux-user: Define target alignment size
Le dimanche 13 février 2011 à 10:24 +0200, Blue Swirl a écrit :
On Sun, Feb 13, 2011 at 4:22 AM, Laurent Vivier laur...@vivier.eu wrote:
Datatype alignment can be found using following application:
int main(void)
{
printf(alignof(short) %ld\n, __alignof__(short));
printf(alignof(int) %ld\n, __alignof__(int));
printf(alignof(long) %ld\n, __alignof__(long));
printf(alignof(long long) %ld\n, __alignof__(long long));
}
This patch includes following alignments:
i386
alignof(short) 2
alignof(int) 4
alignof(long) 4
alignof(long long) 8
x86_64
alignof(short) 2
alignof(int) 4
alignof(long) 8
alignof(long long) 8
arm
alignof(short) 2
alignof(int) 4
alignof(long) 4
alignof(long long) 4
m68k (680x0)
alignof(short) 2
alignof(int) 2
alignof(long) 2
alignof(long long) 2
mips
alignof(short) 2
alignof(int) 4
alignof(long) 4
alignof(long long) 8
ppc
alignof(short) 2
alignof(int) 4
alignof(long) 4
alignof(long long) 8
for other targets, use by default (2,4,4,8).
Please, update for your favorite target...
For Sparc32 (I think also sparc32plus), the default is OK.
For Sparc64, please use 2, 4, 8, 8. I'd guess other 64 bit platforms
(Alpha, MIPS64, PPC64 etc) should use the same.
OK, I update my patch.
Does GCC produce correct code using the attributes on strictly aligned
host, when the target is less strictly aligned?
It seems it is OK. I did some tests into a mips-linux-user chroot (sparc
one is broken ;-) ) :
mips is a strictly aligned host, from gcc/config/mips/mips.h:
#define STRICT_ALIGNMENT 1
aligments are:
alignof(short) 2
alignof(int) 4
alignof(long) 4
alignof(long long) 8
We try to align int on 2.
#include stdio.h
typedef int target_int __attribute__((aligned(2)));
struct {
char Z;
target_int A;
} B;
int main(void)
{
B.A = 0xdeadbeaf;
printf(%d: %x\n, __alignof__(B.A), B.A);
}
./test_align
2: deadbeaf
disass:
lw $2,%got(B)($28)
li $3,-559087616 # 0xdead
ori $3,$3,0xbeaf
swl $3,2($2)
swr $3,5($2)
normal case:
lw $3,%got(B)($28)
li $2,-559087616 # 0xdead
ori $2,$2,0xbeaf
sw $2,4($3)
So, gcc seems smart enough to split the memory access in several ones
compatible with the strict alignment rules.
Should the alignment of floating point variables be specified as well?
At the moment it seems useless.
The strict alignment required for doubles is 4, but recommended
alignment is 8, I'm not sure which one is used for structures
containing doubles.
if necessary, some tests will be helpfull.
Thank you for your comments.
Regards,
Laurent
--
- laur...@vivier.eu --
Tout ce qui est impossible reste à accomplirJules Verne
Things are only impossible until they're not Jean-Luc Picard
[Qemu-devel] [PATCH 1/2] linux-user: Define target alignment size
Datatype alignment can be found using following application:
int main(void)
{
printf(alignof(short) %ld\n, __alignof__(short));
printf(alignof(int) %ld\n, __alignof__(int));
printf(alignof(long) %ld\n, __alignof__(long));
printf(alignof(long long) %ld\n, __alignof__(long long));
}
This patch includes following alignments:
i386
alignof(short) 2
alignof(int) 4
alignof(long) 4
alignof(long long) 8
x86_64
alignof(short) 2
alignof(int) 4
alignof(long) 8
alignof(long long) 8
arm
alignof(short) 2
alignof(int) 4
alignof(long) 4
alignof(long long) 4
m68k (680x0)
alignof(short) 2
alignof(int) 2
alignof(long) 2
alignof(long long) 2
mips
alignof(short) 2
alignof(int) 4
alignof(long) 4
alignof(long long) 8
ppc
alignof(short) 2
alignof(int) 4
alignof(long) 4
alignof(long long) 8
for other targets, use by default (2,4,4,8).
Please, update for your favorite target...
Signed-off-by: Laurent Vivier laur...@vivier.eu
---
v2: compute align size for each basic datatype
configure | 13 +
cpu-defs.h | 14 ++
2 files changed, 23 insertions(+), 4 deletions(-)
diff --git a/configure b/configure
index 25381e5..efc6fa4 100755
--- a/configure
+++ b/configure
@@ -2919,6 +2919,10 @@ target_nptl=no
interp_prefix1=`echo $interp_prefix | sed s/%M/$target_arch2/g`
echo CONFIG_QEMU_INTERP_PREFIX=\$interp_prefix1\ $config_target_mak
gdb_xml_files=
+target_short_alignment=2
+target_int_alignment=4
+target_long_alignment=4
+target_long_long_alignment=8
TARGET_ARCH=$target_arch2
TARGET_BASE_ARCH=
@@ -2931,6 +2935,7 @@ case $target_arch2 in
x86_64)
TARGET_BASE_ARCH=i386
target_phys_bits=64
+target_long_alignment=8
;;
alpha)
target_phys_bits=64
@@ -2942,6 +2947,7 @@ case $target_arch2 in
target_nptl=yes
gdb_xml_files=arm-core.xml arm-vfp.xml arm-vfp3.xml arm-neon.xml
target_phys_bits=32
+target_long_long_alignment=4
;;
cris)
target_nptl=yes
@@ -2951,6 +2957,9 @@ case $target_arch2 in
bflt=yes
gdb_xml_files=cf-core.xml cf-fp.xml
target_phys_bits=32
+target_int_alignment=2
+target_long_alignment=2
+target_long_long_alignment=2
;;
microblaze)
bflt=yes
@@ -3029,6 +3038,10 @@ case $target_arch2 in
exit 1
;;
esac
+echo TARGET_SHORT_ALIGNMENT=$target_short_alignment $config_target_mak
+echo TARGET_INT_ALIGNMENT=$target_int_alignment $config_target_mak
+echo TARGET_LONG_ALIGNMENT=$target_long_alignment $config_target_mak
+echo TARGET_LONG_LONG_ALIGNMENT=$target_long_long_alignment
$config_target_mak
echo TARGET_ARCH=$TARGET_ARCH $config_target_mak
target_arch_name=`echo $TARGET_ARCH | tr '[:lower:]' '[:upper:]'`
echo TARGET_$target_arch_name=y $config_target_mak
diff --git a/cpu-defs.h b/cpu-defs.h
index 8d4bf86..98c6718 100644
--- a/cpu-defs.h
+++ b/cpu-defs.h
@@ -37,16 +37,22 @@
#define TARGET_LONG_SIZE (TARGET_LONG_BITS / 8)
+typedef int16_t target_short __attribute__ ((aligned(TARGET_SHORT_ALIGNMENT)));
+typedef uint16_t target_ushort
__attribute__((aligned(TARGET_SHORT_ALIGNMENT)));
+typedef int32_t target_int __attribute__((aligned(TARGET_INT_ALIGNMENT)));
+typedef uint32_t target_uint __attribute__((aligned(TARGET_INT_ALIGNMENT)));
+typedef int64_t target_long_long
__attribute__((aligned(TARGET_LONG_LONG_ALIGNMENT)));
+typedef uint64_t target_ulong_long
__attribute__((aligned(TARGET_LONG_LONG_ALIGNMENT)));
/* target_ulong is the type of a virtual address */
#if TARGET_LONG_SIZE == 4
-typedef int32_t target_long;
-typedef uint32_t target_ulong;
+typedef int32_t target_long __attribute__((aligned(TARGET_LONG_ALIGNMENT)));
+typedef uint32_t target_ulong __attribute__((aligned(TARGET_LONG_ALIGNMENT)));
#define TARGET_FMT_lx %08x
#define TARGET_FMT_ld %d
#define TARGET_FMT_lu %u
#elif TARGET_LONG_SIZE == 8
-typedef int64_t target_long;
-typedef uint64_t target_ulong;
+typedef int64_t target_long __attribute__((aligned(TARGET_LONG_ALIGNMENT)));
+typedef uint64_t target_ulong __attribute__((aligned(TARGET_LONG_ALIGNMENT)));
#define TARGET_FMT_lx %016 PRIx64
#define TARGET_FMT_ld % PRId64
#define TARGET_FMT_lu % PRIu64
--
1.7.1
