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openssl: avoid OPENSSL_SMALL_FOOTPRINT, no-asm 

Building openssl with OPENSSL_SMALL_FOOTPRINT yelds only from 1% to 3%
decrease in size, dropping performance from 2% to 91%, depending on the
target and algorithm.

For example, using AES256-GCM with 1456-bytes operations, X86_64 appears
to be the least affected with 2% performance penalty and 1% reduction in
size; mips drops performance by 13%, size by 3%;  Arm drops 29% in
performance, 2% in size.

On aarch64, it slows down ghash so much that I consider it broken
(-91%).  SMALL_FOOTPRINT will reduce AES256-GCM performance by 88%, and
size by only 1%.  It makes an AES-capable CPU run AES128-GCM at 35% of
the speed of Chacha20-Poly1305:

Block-size=1456 bytes   AES256-GCM   AES128-GCM  ChaCha20-Poly1305
SMALL_FOOTPRINT           62014.44     65063.23          177090.50
regular                  504220.08    565630.28          182706.16

OpenSSL 1.1.1 numbers are about the same, so this should have been
noticed a long time ago.

This creates an option to use OPENSSL_SMALL_FOOTPRINT, but it is turned
off by default unless SMALL_FLASH or LOW_MEMORY_FOOTPRINT is used.

Compiling with -O3 instead of -Os, for comparison, will increase size by
about 14-15%, with no measureable effect on AES256-GCM performance, and
about 2% increase in Chacha20-Poly1305 performance on Aarch64.

There are no Arm devices with the small flash feature, so drop the
conditional default.  The package is built on phase2, so even if we
include an Arm device with small flash later, a no-asm library would
have to be built from source anyway.

Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>
This commit is contained in:
Eneas U de Queiroz 2023-03-10 17:21:11 -03:00
parent 75f7e2d10b
commit 975036f6f9
No known key found for this signature in database
GPG Key ID: A1FE5A85EFAE657D
2 changed files with 21 additions and 4 deletions
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18
package/libs/openssl/Config.in
View File

@ -12,9 +12,23 @@ config OPENSSL_OPTIMIZE_SPEED
The increase in performance and size depends on the
target CPU. EC and AES seem to benefit the most.
config OPENSSL_SMALL_FOOTPRINT
bool
depends on !OPENSSL_OPTIMIZE_SPEED
default y if SMALL_FLASH || LOW_MEMORY_FOOTPRINT
prompt "Build with OPENSSL_SMALL_FOOTPRINT (read help)"
help
This turns on -DOPENSSL_SMALL_FOOTPRINT. This will save only
1-3% of of the ipk size. The performance drop depends on
architecture and algorithm. MIPS drops 13% of performance for
a 3% decrease in ipk size. On Aarch64, for a 1% reduction in
size, ghash and GCM performance decreases 90%, while
Chacha20-Poly1305 is 15% slower. X86_64 drops 1% of its size
for 3% of performance. Other arches have not been tested.
config OPENSSL_WITH_ASM
bool
default y if !SMALL_FLASH || !arm
default y
prompt "Compile with optimized assembly code"
depends on !arc
help
@ -46,7 +60,7 @@ config OPENSSL_NO_DEPRECATED
config OPENSSL_WITH_ERROR_MESSAGES
bool
default y if !SMALL_FLASH && !LOW_MEMORY_FOOTPRINT
default y if !OPENSSL_SMALL_FOOTPRINT || (!SMALL_FLASH && !LOW_MEMORY_FOOTPRINT)
prompt "Include error messages"
help
This option aids debugging, but increases package size and

7
package/libs/openssl/Makefile
View File

@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
PKG_NAME:=openssl
PKG_VERSION:=3.0.8
PKG_RELEASE:=4
PKG_RELEASE:=5
PKG_BUILD_FLAGS:=no-mips16 gc-sections
PKG_BUILD_PARALLEL:=1
@ -39,6 +39,7 @@ PKG_CONFIG_DEPENDS:= \
CONFIG_OPENSSL_NO_DEPRECATED \
CONFIG_OPENSSL_OPTIMIZE_SPEED \
CONFIG_OPENSSL_PREFER_CHACHA_OVER_GCM \
CONFIG_OPENSSL_SMALL_FOOTPRINT \
CONFIG_OPENSSL_WITH_ARIA \
CONFIG_OPENSSL_WITH_ASM \
CONFIG_OPENSSL_WITH_ASYNC \
@ -258,7 +259,9 @@ endif
ifeq ($(CONFIG_OPENSSL_OPTIMIZE_SPEED),y)
TARGET_CFLAGS := $(filter-out -O%,$(TARGET_CFLAGS)) -O3
else
endif
ifeq ($(CONFIG_OPENSSL_SMALL_FOOTPRINT),y)
OPENSSL_OPTIONS += -DOPENSSL_SMALL_FOOTPRINT
endif