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i386: make stack size optimization selectable, and allow i486 insns (bswap)

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It's hard to imagine someone still using non-bswap equipped CPU

function                                             old     new   delta
xmalloc_optname_optval                               888     879      -9
write_leases                                         214     205      -9
write32                                               36      27      -9
update_status                                        612     603      -9
udhcpd_main                                         1468    1459      -9
udhcpc_main                                         2708    2699      -9
udhcp_run_script                                     804     795      -9
sha256_process_block64                               423     414      -9
sha1_process_block64                                 337     328      -9
sha1_end                                              80      71      -9
send_ACK                                             161     152      -9
select_lease_time                                     64      55      -9
rpm_getint                                           118     109      -9
readprofile_main                                    1719    1710      -9
read32                                                33      24      -9
rdate_main                                           236     227      -9
machtime                                              39      30      -9
inet_addr_match                                      103      94      -9
get_prefix                                           344     335      -9
f_write32                                             31      22      -9
f_read32                                              31      22      -9
dumpleases_main                                      620     611      -9
KeyExpansion                                         197     188      -9
udhcp_str2optset                                     536     518     -18
read_config                                          222     204     -18
lfp_to_d                                              55      37     -18
ipaddr_modify                                       1226    1208     -18
dnsd_main                                           1278    1260     -18
des_crypt                                           1344    1326     -18
d_to_lfp                                             106      88     -18
bb_bswap_64                                           29      11     -18
INET_setroute                                        827     809     -18
read_leases                                          330     309     -21
zcip_main                                           1256    1229     -27
send_offer                                           476     449     -27
ipcalc_main                                          534     507     -27
handle_incoming_and_exit                            2821    2794     -27
fmt_time_bernstein_25                                131     104     -27
common_traceroute_main                              3804    3768     -36
rpm_gettags                                          451     397     -54
parse_args                                          1412    1358     -54
volume_id_probe_hfs_hfsplus                          627     564     -63
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/42 up/down: 0/-732)          Total: -732 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2018-04-06 18:55:35 +02:00
parent 2ab994f707
commit 2c99702810
2 changed files with 15 additions and 1 deletions
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8
Config.in
View File

@ -518,6 +518,14 @@ config USE_PORTABLE_CODE
compiler other than gcc.
If you do use gcc, this option may needlessly increase code size.
config STACK_OPTIMIZATION_386
bool "Use -mpreferred-stack-boundary=2 on i386 arch"
default y
help
This option makes for smaller code, but some libc versions
do not work with it (they use SSE instructions without
ensuring stack alignment).
comment 'Installation Options ("make install" behavior)'
choice

8
arch/i386/Makefile
View File

@ -2,6 +2,12 @@
# Build system
# ==========================================================================
# Allow i486 insns (basically, bswap insn)
# Do not try to tune for 486+ (might add padding)
CFLAGS += $(call cc-option,-march=i486 -mtune=i386,)
ifeq ($(CONFIG_STACK_OPTIMIZATION_386),y)
# -mpreferred-stack-boundary=2 is essential in preventing gcc 4.2.x
# from aligning stack to 16 bytes. (Which is gcc's way of supporting SSE).
CFLAGS += $(call cc-option,-march=i386 -mpreferred-stack-boundary=2,)
CFLAGS += $(call cc-option,-mpreferred-stack-boundary=2,)
endif