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x86-64/swapcontext: Restore the pointer into %rdx after syscall

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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 <hjl.tools@gmail.com>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

	* 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.
This commit is contained in:
H.J. Lu 2018-04-26 05:01:20 -07:00
parent 556f5c46c7
commit 15c19147a8
1 changed files with 21 additions and 19 deletions
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40
sysdeps/unix/sysv/linux/x86_64/swapcontext.S
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@ -79,38 +79,40 @@ ENTRY(__swapcontext)
cmpq $-4095, %rax /* Check %rax for error. */ cmpq $-4095, %rax /* Check %rax for error. */
jae SYSCALL_ERROR_LABEL /* Jump to error handler if error. */ jae SYSCALL_ERROR_LABEL /* Jump to error handler if error. */
/* Restore destroyed registers. */ /* Restore destroyed register into RDX. The choice is arbitrary,
movq %r12, %rsi 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 /* Restore the floating-point context. Not the registers, only the
rest. */ rest. */
movq oFPREGS(%rsi), %rcx movq oFPREGS(%rdx), %rcx
fldenv (%rcx) fldenv (%rcx)
ldmxcsr oMXCSR(%rsi) ldmxcsr oMXCSR(%rdx)
/* Load the new stack pointer and the preserved registers. */ /* Load the new stack pointer and the preserved registers. */
movq oRSP(%rsi), %rsp movq oRSP(%rdx), %rsp
movq oRBX(%rsi), %rbx movq oRBX(%rdx), %rbx
movq oRBP(%rsi), %rbp movq oRBP(%rdx), %rbp
movq oR12(%rsi), %r12 movq oR12(%rdx), %r12
movq oR13(%rsi), %r13 movq oR13(%rdx), %r13
movq oR14(%rsi), %r14 movq oR14(%rdx), %r14
movq oR15(%rsi), %r15 movq oR15(%rdx), %r15
/* The following ret should return to the address set with /* The following ret should return to the address set with
getcontext. Therefore push the address on the stack. */ getcontext. Therefore push the address on the stack. */
movq oRIP(%rsi), %rcx movq oRIP(%rdx), %rcx
pushq %rcx pushq %rcx
/* Setup registers used for passing args. */ /* Setup registers used for passing args. */
movq oRDI(%rsi), %rdi movq oRDI(%rdx), %rdi
movq oRDX(%rsi), %rdx movq oRSI(%rdx), %rsi
movq oRCX(%rsi), %rcx movq oRCX(%rdx), %rcx
movq oR8(%rsi), %r8 movq oR8(%rdx), %r8
movq oR9(%rsi), %r9 movq oR9(%rdx), %r9
/* Setup finally %rsi. */ /* Setup finally %rdx. */
movq oRSI(%rsi), %rsi movq oRDX(%rdx), %rdx
/* Clear rax to indicate success. */ /* Clear rax to indicate success. */
xorl %eax, %eax xorl %eax, %eax