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compel: x86 parasite_service entry point simplification

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We don't need to push 0 on the stack. This seems to be a remnant of the
initial commit of 2011 that had a `pushq $0`.

The 16 bytes %rsp alignment was added with commit 2a0cea29 in 2012.
This is no longer necessary as we already guarantee that %rsp is 16
bytes aligned. A BUG_ON() is added to enforce this guarantee.

Signed-off-by: Nicolas Viennot <Nicolas.Viennot@twosigma.com>
This commit is contained in:
Nicolas Viennot 2020-07-17 02:39:52 +00:00 • committed by Dmitry Safonov
parent d7353b9bb7
commit ea263bc472
2 changed files with 13 additions and 10 deletions
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12
compel/arch/x86/plugins/std/parasite-head.S
View file

@ -6,14 +6,6 @@
# error 64-bit parasite should compile with CONFIG_X86_64
#endif
.macro PARASITE_ENTRY num
subq $16, %rsp
andq $~15, %rsp
pushq $\num
movq %rsp, %rbp
call parasite_service
.endm
#ifdef CONFIG_COMPAT
.code32
ENTRY(__export_parasite_head_start_compat)
@ -21,7 +13,7 @@ ENTRY(__export_parasite_head_start_compat)
jmp $__USER_CS,$1f
1:
.code64
PARASITE_ENTRY 0
call parasite_service
pushq $__USER32_CS
xor %r11, %r11
movl $2f, %r11d
@ -43,6 +35,6 @@ END(__export_parasite_head_start_compat)
#endif
ENTRY(__export_parasite_head_start)
PARASITE_ENTRY 0
call parasite_service
int $0x03
END(__export_parasite_head_start)

11
compel/src/lib/infect.c
View file

@ -948,6 +948,17 @@ int compel_infect(struct parasite_ctl *ctl, unsigned long nr_threads, unsigned l
p += PARASITE_STACK_SIZE;
ctl->rstack = ctl->remote_map + p;
/*
* x86-64 ABI requires a 16 bytes aligned stack.
* It is already the case as RESTORE_STACK_SIGFRAME is a multiple of
* 64, and PARASITE_STACK_SIZE is 0x4000.
*/
if ((unsigned long)ctl->rstack & (16-1)) {
pr_err("BUG: stack is not 16 bytes aligned: %p\n", ctl->rstack);
ctl->rstack = (void *)round_down((unsigned long)ctl->rstack, 16);
}
if (nr_threads > 1) {
p += PARASITE_STACK_SIZE;
ctl->r_thread_stack = ctl->remote_map + p;