@@ -213,14 +213,19 @@ __morestack_non_split:
cmpl $0x185d8d4c,(%rax)
je 2f
- # This breaks call/return prediction, as described above.
- incq 8(%rsp) # Increment the return address.
+ movq %rax,-8(%rsp) # Save the incremented return
+ # address to the red-zone below
+ # the stack pointer. It is
+ # guaranteed not to be corrupted.
popq %rax # Restore register.
.cfi_adjust_cfa_offset -8 # Adjust for popped register.
- ret # Return to caller.
+ callq *-16(%rsp) # Call into the caller's
+ # function body.
+
+ ret # Return to caller's prologue.
2:
popq %rax # Restore register.
This patch fixed a broken call/return address prediction in segmented stack implementation on x86_64 by leveraging the red-zone under the stack pointer. 2022-01-06 Zhiyao Ma <zhiyao.ma@yale.edu> libgcc/ChangeLog: * config/i386/morestack.S: Modified instructions. --- libgcc/config/i386/morestack.S | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) -- 2.25.1