Stack protector adds extra mov, extra stack allocation and extra branch
to save and validate the stack canary. While this feature could be
useful to detect stack corruption in some scenarios, it is not really
needed for liburing which is simple enough to review.
Good code shouldn't corrupt the stack. We don't need this extra
checking at the moment. Just for comparison, let's take a hot function
__io_uring_get_cqe.
Before this patch:
```
0000000000002b80 <__io_uring_get_cqe>:
2b80: f3 0f 1e fa endbr64
2b84: 48 83 ec 28 sub $0x28,%rsp
2b88: 64 48 8b 04 25 28 00 mov %fs:0x28,%rax
2b8f: 00 00
2b91: 48 89 44 24 18 mov %rax,0x18(%rsp)
2b96: 31 c0 xor %eax,%eax
2b98: 89 14 24 mov %edx,(%rsp)
2b9b: 48 89 e2 mov %rsp,%rdx
2b9e: 48 b8 00 00 00 00 08 movabs $0x800000000,%rax
2ba5: 00 00 00
2ba8: 89 4c 24 04 mov %ecx,0x4(%rsp)
2bac: 48 89 44 24 08 mov %rax,0x8(%rsp)
2bb1: 4c 89 44 24 10 mov %r8,0x10(%rsp)
2bb6: e8 45 fe ff ff call 2a00 <_io_uring_get_cqe>
2bbb: 48 8b 54 24 18 mov 0x18(%rsp),%rdx
2bc0: 64 48 2b 14 25 28 00 sub %fs:0x28,%rdx
2bc7: 00 00
2bc9: 75 05 jne 2bd0 <__io_uring_get_cqe+0x50>
2bcb: 48 83 c4 28 add $0x28,%rsp
2bcf: c3 ret
2bd0: e8 9b f5 ff ff call 2170 <__stack_chk_fail@plt>
2bd5: 66 66 2e 0f 1f 84 00 data16 cs nopw 0x0(%rax,%rax,1)
2bdc: 00 00 00 00
```
After this patch:
```
0000000000002ab0 <__io_uring_get_cqe>:
2ab0: f3 0f 1e fa endbr64
2ab4: 48 b8 00 00 00 00 08 movabs $0x800000000,%rax
2abb: 00 00 00
2abe: 48 83 ec 28 sub $0x28,%rsp
2ac2: 89 14 24 mov %edx,(%rsp)
2ac5: 48 89 e2 mov %rsp,%rdx
2ac8: 89 4c 24 04 mov %ecx,0x4(%rsp)
2acc: 48 89 44 24 08 mov %rax,0x8(%rsp)
2ad1: 4c 89 44 24 10 mov %r8,0x10(%rsp)
2ad6: e8 55 fe ff ff call 2930 <_io_uring_get_cqe>
2adb: 48 83 c4 28 add $0x28,%rsp
2adf: c3 ret
```
Previously, we only use `-fno-stack-protector` for nolibc build as the
stack protector needs to call `__stack_chk_fail@plt` function from the
libc. Now, we always use `-fno-stack-protector` for both nolibc and
libc builds to generate shorter Assembly code.
Cc: Nugra <richiisei@gmail.com>
Cc: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>
Cc: GNU/Weeb Mailing List <gwml@vger.gnuweeb.org>
Cc: Tea Inside Mailing List <timl@vger.teainside.org>
Cc: io-uring Mailing List <io-uring@vger.kernel.org>
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---
src/Makefile | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/src/Makefile b/src/Makefile
index cc6c871..3e1192f 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -8,7 +8,7 @@ libdevdir ?= $(prefix)/lib
CPPFLAGS ?=
override CPPFLAGS += -D_GNU_SOURCE \
-Iinclude/ -include ../config-host.h
-CFLAGS ?= -g -fomit-frame-pointer -O2 -Wall -Wextra
+CFLAGS ?= -g -fomit-frame-pointer -O2 -Wall -Wextra -fno-stack-protector
override CFLAGS += -Wno-unused-parameter -Wno-sign-compare -DLIBURING_INTERNAL
SO_CFLAGS=-fPIC $(CFLAGS)
L_CFLAGS=$(CFLAGS)
@@ -36,8 +36,8 @@ liburing_srcs := setup.c queue.c register.c
ifeq ($(CONFIG_NOLIBC),y)
liburing_srcs += nolibc.c
- override CFLAGS += -nostdlib -nodefaultlibs -ffreestanding -fno-stack-protector
- override CPPFLAGS += -nostdlib -nodefaultlibs -ffreestanding -fno-stack-protector
+ override CFLAGS += -nostdlib -nodefaultlibs -ffreestanding
+ override CPPFLAGS += -nostdlib -nodefaultlibs -ffreestanding
override LINK_FLAGS += -nostdlib -nodefaultlibs
else
liburing_srcs += syscall.c
base-commit: 896a1d3ab14a8777a45db6e7b67cf557a44923fb
--
2.32.0