From 15c19147a8361b7281519b9784b3b823c447cf7a Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Thu, 26 Apr 2018 05:01:20 -0700 Subject: x86-64/swapcontext: Restore the pointer into %rdx after syscall To prepare for shadow stack support, restore the pointer into %rdx after syscall and use %rdx, instead of %rsi, to restore context. There is no functional change. Signed-off-by: H.J. Lu Reviewed-by: Carlos O'Donell * sysdeps/unix/sysv/linux/x86_64/swapcontext.S (__swapcontext): Restore the pointer into %rdx, after syscall and use %rdx, instead of %rsi, to restore context. --- sysdeps/unix/sysv/linux/x86_64/swapcontext.S | 42 +++++++++++++++------------- 1 file changed, 22 insertions(+), 20 deletions(-) (limited to 'sysdeps/unix/sysv/linux/x86_64/swapcontext.S') diff --git a/sysdeps/unix/sysv/linux/x86_64/swapcontext.S b/sysdeps/unix/sysv/linux/x86_64/swapcontext.S index e577c209b9..1110c479fa 100644 --- a/sysdeps/unix/sysv/linux/x86_64/swapcontext.S +++ b/sysdeps/unix/sysv/linux/x86_64/swapcontext.S @@ -79,38 +79,40 @@ ENTRY(__swapcontext) cmpq $-4095, %rax /* Check %rax for error. */ jae SYSCALL_ERROR_LABEL /* Jump to error handler if error. */ - /* Restore destroyed registers. */ - movq %r12, %rsi + /* Restore destroyed register into RDX. The choice is arbitrary, + but leaving RDI and RSI available for use later can avoid + shuffling values. */ + movq %r12, %rdx /* Restore the floating-point context. Not the registers, only the rest. */ - movq oFPREGS(%rsi), %rcx + movq oFPREGS(%rdx), %rcx fldenv (%rcx) - ldmxcsr oMXCSR(%rsi) + ldmxcsr oMXCSR(%rdx) /* Load the new stack pointer and the preserved registers. */ - movq oRSP(%rsi), %rsp - movq oRBX(%rsi), %rbx - movq oRBP(%rsi), %rbp - movq oR12(%rsi), %r12 - movq oR13(%rsi), %r13 - movq oR14(%rsi), %r14 - movq oR15(%rsi), %r15 + movq oRSP(%rdx), %rsp + movq oRBX(%rdx), %rbx + movq oRBP(%rdx), %rbp + movq oR12(%rdx), %r12 + movq oR13(%rdx), %r13 + movq oR14(%rdx), %r14 + movq oR15(%rdx), %r15 /* The following ret should return to the address set with getcontext. Therefore push the address on the stack. */ - movq oRIP(%rsi), %rcx + movq oRIP(%rdx), %rcx pushq %rcx /* Setup registers used for passing args. */ - movq oRDI(%rsi), %rdi - movq oRDX(%rsi), %rdx - movq oRCX(%rsi), %rcx - movq oR8(%rsi), %r8 - movq oR9(%rsi), %r9 - - /* Setup finally %rsi. */ - movq oRSI(%rsi), %rsi + movq oRDI(%rdx), %rdi + movq oRSI(%rdx), %rsi + movq oRCX(%rdx), %rcx + movq oR8(%rdx), %r8 + movq oR9(%rdx), %r9 + + /* Setup finally %rdx. */ + movq oRDX(%rdx), %rdx /* Clear rax to indicate success. */ xorl %eax, %eax -- cgit 1.4.1