https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83970
Bug ID: 83970
Summary: -mindirect-branch=thunk -fno-plt generates
CET-incompatible thunk
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: hjl.tools at gmail dot com
Target Milestone: ---
Target: x86
[hjl@gnu-bdx-1 indirect-got-1]$ cat x.i
void func (void);
void
bar (void)
{
func ();
}
[hjl@gnu-bdx-1 indirect-got-1]$
/export/build/gnu/gcc-test/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc-test/build-x86_64-linux/gcc/ -O2
-mindirect-branch=thunk -fno-plt -S x.i
[hjl@gnu-bdx-1 indirect-got-1]$ cat x.s
.file "x.i"
.text
.p2align 4,,15
.globl bar
.type bar, @function
bar:
.LFB0:
.cfi_startproc
pushq func@GOTPCREL(%rip)
jmp __x86_indirect_thunk
.cfi_endproc
.LFE0:
.size bar, .-bar
.section
.text.__x86_indirect_thunk,"axG",@progbits,__x86_indirect_thunk,comdat
.globl __x86_indirect_thunk
.hidden __x86_indirect_thunk
.type __x86_indirect_thunk, @function
__x86_indirect_thunk:
.set __x86_return_thunk,__x86_indirect_thunk
.globl __x86_return_thunk
.hidden __x86_return_thunk
.LFB1:
.cfi_startproc
call .LIND1
.LIND0:
pause
lfence
jmp .LIND0
.LIND1:
lea 8(%rsp), %rsp
ret
.cfi_endproc
.LFE1:
.ident "GCC: (GNU) 8.0.1 20180115 (experimental)"
.section .note.GNU-stack,"",@progbits
[hjl@gnu-bdx-1 indirect-got-1]$
For i386, since all registers may be used for function call, there
isn't much we can do. But there are a couple scratch registers
available for function call. We can generate
bar:
.LFB0:
.cfi_startproc
movq func@GOTPCREL(%rip), %r11
jmp __x86_indirect_thunk_r11
.cfi_endproc
.LFE0:
.size bar, .-bar
which is easier to change __x86_indirect_thunk_r11 to be compatible
with CET.
