Computed lengths are used as 32 bit values, even when they are less
than 128. Symbols assigned values less than 128 and used generate
a one byte immediate in pushl $value, while symbols with computed
lengths appear as 4 byte immediate values, even though they have the
same small value.
Alan
azp:68% cat b.s ; as -a b.s -o b.o
.text
msg: .asciz "hello world.\n"
msglen = .-msg-1 # determine length, an absolute value
#msglen=msglen & 0xff # this crashes the assembler if included
foo = 13
pushl $13 # this generates a 2 byte instruction
pushl $msglen # this generates 4 bytes for the same
pushl $foo # but this generates 2 bytes
pushl msg
GAS LISTING b.s page 1
1 .text
2
3 0000 68656C6C msg: .asciz "hello world.\n"
3 6F20776F
3 726C642E
3 0A00
4 msglen = .-msg-1 # determine length, an
absolute value
5 #msglen=msglen & 0xff # this crashes the
assembler if included
6 foo = 13
7
8 000e 6A0D pushl $13 # this generates a 2
byte instruction
9 0010 680D0000 pushl $msglen # this generates 4 bytes
for the same
9 00
10 0015 6A0D pushl $foo # but this generates 2
bytes
11 0017 FF350000 pushl msg
11 00008D76
11 00
GAS LISTING b.s page 2
DEFINED SYMBOLS
b.s:3 .text:00000000 msg
*ABS*:0000000d msglen
*ABS*:0000000d foo
NO UNDEFINED SYMBOLS
--
Summary: generates non-optimal instruction...
Product: binutils
Version: 2.12.1
Status: NEW
Severity: normal
Priority: P2
Component: gas
AssignedTo: unassigned at sources dot redhat dot com
ReportedBy: larson at w6yx dot stanford dot edu
CC: bug-binutils at gnu dot org
GCC host triplet: Freebsd i386
GCC target triplet: i386
http://sources.redhat.com/bugzilla/show_bug.cgi?id=998
------- You are receiving this mail because: -------
You are on the CC list for the bug, or are watching someone who is.
_______________________________________________
bug-binutils mailing list
bug-binutils@gnu.org
http://lists.gnu.org/mailman/listinfo/bug-binutils
