This page is a draft. Please help enhancing it by adding lines and filling tables. Comments at the bottom of the text are also welcome.
This is just a quick array to recall some of the specifics of the architectures found in the Debian project.
feature |
alpha |
amd64, kfreebsd-amd64 |
arm |
hppa |
i386, kfreebsd-i386, hurd-i386 |
ia64 |
s390 |
||||||
size of short |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
size of int |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
size of long |
8 |
8 |
4 |
4 |
4 |
4 |
8 |
4 |
4 |
4 |
4 |
4 |
4 |
size of long long |
8 |
8 |
8 |
8 |
8 |
8 |
8 |
8 |
8 |
8 |
8 |
8 |
8 |
size of float |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
size of double |
8 |
8 |
8 |
8 |
8 |
8 |
8 |
8 |
8 |
8 |
8 |
8 |
8 |
size of long double |
16 (8) |
16 |
8 |
8 |
8 |
12 |
16 |
12 |
8 |
8 |
16 (8) |
16 (8) |
16 (8) |
size of data pointer |
8 |
8 |
4 |
4 |
4 |
4 |
8 |
4 |
4 |
4 |
4 |
4 |
4 |
max alignment |
8 |
8 |
4 |
8 |
? |
4 (16) |
8 |
? |
8 |
8 |
? |
? |
? |
unaligned access OK |
no |
yes |
yes |
? |
no |
yes |
no |
yes |
no |
no |
yes |
? |
no |
endianness |
little |
little |
little |
little |
big |
little |
little |
big |
big |
little |
big |
big |
big |
char signedness |
? |
s |
u |
u |
s |
s |
s |
s |
s |
s |
u |
? |
s |
stack grows |
down |
down |
down |
down |
up |
down |
down |
down |
down |
down |
down |
? |
down |
func param location |
regs |
regs |
regs |
regs |
? |
stack |
regs |
stack |
regs |
regs |
regs |
regs |
regs |
func return ptr location |
reg |
stack |
reg |
reg |
? |
stack |
reg |
stack |
reg |
reg |
reg |
? |
reg |
page size(s) |
8K |
4K, 2M |
4K |
4K |
? |
4K, 2M/4M |
? |
4K |
4K-64K |
4K-64K |
? |
4K |
? |
Signedness
When programming in C, variables can be signed or unsigned.
Example:
unsigned char c; |
explicit unsigned, 0 <= c <= 255 |
signed char c; |
explicit signed, -128 <= c <= 127 |
char c; |
implicit (un)signedness, depending on architecture |
To force a signedness, either declare it explicitly or use the gcc command line option -f(un)signed-char. The gcc defaults differ only due to optimisation. Other compilers may not have this issue.
Obtaining this information via autoconf
AC_INIT(archtest, 0.1) AC_CHECK_SIZEOF(short) AC_CHECK_SIZEOF(int) AC_CHECK_SIZEOF(long) AC_CHECK_SIZEOF(long long) AC_CHECK_SIZEOF(float) AC_CHECK_SIZEOF(double) AC_CHECK_SIZEOF(long double) AC_CHECK_SIZEOF(void*) AC_C_BIGENDIAN() AC_C_CHAR_UNSIGNED()