https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92841
Bug ID: 92841
Summary: Optimize -fstack-protector-strong code generation a
bit
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: bp at alien8 dot de
Target Milestone: ---
Created attachment 47435
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47435&action=edit
prepocessed source
Hi,
I'm building the linux kernel with
gcc (Debian 9.2.1-8) 9.2.1 20190909
and -fstack-protector-strong on x86 and from looking at what it generates, it
could be optimized a little:
# arch/x86/kernel/cpu/scattered.c:48: {
movq %gs:40, %rax # MEM[(<address-space-2> long unsigned int
*)40B], tmp125
movq %rax, 16(%rsp) # tmp125, D.21425
xorl %eax, %eax # tmp125
movl $6, %eax #, pretmp_35
jmp .L6 #
AFAICT, the stack protector part would load the canary value from the %gs
offset and use a temp register to stick it on the stack and then clear that
temp register, %rax in this case.
As part of further function processing, it would stick a value in that same
register, which makes the previous clearing superfluous.
I'm being told this could be taken care of in a "late peephole". :)
Attaching preprocessed source.
Thx.
