These changes are the raw update to linux-4.4.6-rt14. Kernel sources

[kvmfornfv.git] / kernel / arch / x86 / entry / vdso / vdso32 / system_call.S

diff --git a/kernel/arch/x86/entry/vdso/vdso32/system_call.S b/kernel/arch/x86/entry/vdso/vdso32/system_call.S
new file mode 100644 (file)
index 0000000..3a1d929
--- /dev/null
+++ b/kernel/arch/x86/entry/vdso/vdso32/system_call.S
@@ -0,0 +1,89 @@
+/*
+ * AT_SYSINFO entry point
+*/
+
+#include <asm/dwarf2.h>
+#include <asm/cpufeature.h>
+#include <asm/alternative-asm.h>
+
+/*
+ * First get the common code for the sigreturn entry points.
+ * This must come first.
+ */
+#include "sigreturn.S"
+
+       .text
+       .globl __kernel_vsyscall
+       .type __kernel_vsyscall,@function
+       ALIGN
+__kernel_vsyscall:
+       CFI_STARTPROC
+       /*
+        * Reshuffle regs so that all of any of the entry instructions
+        * will preserve enough state.
+        *
+        * A really nice entry sequence would be:
+        *  pushl %edx
+        *  pushl %ecx
+        *  movl  %esp, %ecx
+        *
+        * Unfortunately, naughty Android versions between July and December
+        * 2015 actually hardcode the traditional Linux SYSENTER entry
+        * sequence.  That is severely broken for a number of reasons (ask
+        * anyone with an AMD CPU, for example).  Nonetheless, we try to keep
+        * it working approximately as well as it ever worked.
+        *
+        * This link may eludicate some of the history:
+        *   https://android-review.googlesource.com/#/q/Iac3295376d61ef83e713ac9b528f3b50aa780cd7
+        * personally, I find it hard to understand what's going on there.
+        *
+        * Note to future user developers: DO NOT USE SYSENTER IN YOUR CODE.
+        * Execute an indirect call to the address in the AT_SYSINFO auxv
+        * entry.  That is the ONLY correct way to make a fast 32-bit system
+        * call on Linux.  (Open-coding int $0x80 is also fine, but it's
+        * slow.)
+        */
+       pushl   %ecx
+       CFI_ADJUST_CFA_OFFSET   4
+       CFI_REL_OFFSET          ecx, 0
+       pushl   %edx
+       CFI_ADJUST_CFA_OFFSET   4
+       CFI_REL_OFFSET          edx, 0
+       pushl   %ebp
+       CFI_ADJUST_CFA_OFFSET   4
+       CFI_REL_OFFSET          ebp, 0
+
+       #define SYSENTER_SEQUENCE       "movl %esp, %ebp; sysenter"
+       #define SYSCALL_SEQUENCE        "movl %ecx, %ebp; syscall"
+
+#ifdef CONFIG_X86_64
+       /* If SYSENTER (Intel) or SYSCALL32 (AMD) is available, use it. */
+       ALTERNATIVE_2 "", SYSENTER_SEQUENCE, X86_FEATURE_SYSENTER32, \
+                         SYSCALL_SEQUENCE,  X86_FEATURE_SYSCALL32
+#else
+       ALTERNATIVE "", SYSENTER_SEQUENCE, X86_FEATURE_SEP
+#endif
+
+       /* Enter using int $0x80 */
+       int     $0x80
+GLOBAL(int80_landing_pad)
+
+       /*
+        * Restore EDX and ECX in case they were clobbered.  EBP is not
+        * clobbered (the kernel restores it), but it's cleaner and
+        * probably faster to pop it than to adjust ESP using addl.
+        */
+       popl    %ebp
+       CFI_RESTORE             ebp
+       CFI_ADJUST_CFA_OFFSET   -4
+       popl    %edx
+       CFI_RESTORE             edx
+       CFI_ADJUST_CFA_OFFSET   -4
+       popl    %ecx
+       CFI_RESTORE             ecx
+       CFI_ADJUST_CFA_OFFSET   -4
+       ret
+       CFI_ENDPROC
+
+       .size __kernel_vsyscall,.-__kernel_vsyscall
+       .previous