x86/cpu: fix data/stack alignment

3 files changed, 28 insertions, 3 deletions

diff --git a/arch/x86/machine/cpu.c b/arch/x86/machine/cpu.c
index 350c7c49..4ceb5e7f 100644
--- a/arch/x86/machine/cpu.c
+++ b/arch/x86/machine/cpu.c
@@ -118,9 +118,15 @@ struct cpu_pseudo_desc {
     uintptr_t address;
 } __packed;
 
+#ifdef __LP64__
+#define cpu_exc_frame_attrs
+#else /* __LP64__ */
+#define cpu_exc_frame_attrs __packed
+#endif /* __LP64__ */
+
 struct cpu_exc_frame {
     unsigned long words[CPU_EXC_FRAME_SIZE];
-};
+} cpu_exc_frame_attrs;
 
 /*
  * Type for low level exception handlers.
diff --git a/arch/x86/machine/cpu.h b/arch/x86/machine/cpu.h
index 01d1d39f..2ce14028 100644
--- a/arch/x86/machine/cpu.h
+++ b/arch/x86/machine/cpu.h
@@ -90,9 +90,16 @@
 #define CPU_WORD_SIZE (LONG_BIT / 8)
 
 /*
- * Data alignment, normally the word size.
+ * Data alignment.
+ *
+ * This is used to align regions of memory that can store any type of
+ * data, such as stacks and sections. The modern i386 as well as the
+ * amd64 System V ABIs both mandate 16 byte data alignment. Kernel
+ * software could use smaller alignments, but this one is meant to
+ * be linked against static libraries, and in particular libgcc, which
+ * are built for standard ABIs.
  */
-#define CPU_DATA_ALIGN CPU_WORD_SIZE
+#define CPU_DATA_ALIGN 16
 
 /*
  * Function alignment.
diff --git a/arch/x86/machine/cpu_asm.S b/arch/x86/machine/cpu_asm.S
index ff9c6e9a..24d44797 100644
--- a/arch/x86/machine/cpu_asm.S
+++ b/arch/x86/machine/cpu_asm.S
@@ -120,6 +120,10 @@
 .endr
 .endm
 
+/*
+ * Note that, unlike i386, the CPU aligns the stack frame to 16 bytes,
+ * and skipping the red zone keeps the stack pointer correctly aligned.
+ */
 .macro cpu_ll_exc_enter vector
     pushq %rbx                              /* save registers used for */
     pushq %rax                              /* stack switching */
@@ -146,6 +150,7 @@
 .macro cpu_ll_exc_handle vector
     cpu_ll_exc_enter \vector
     movq %rbx, %rdi
+    andq $(~(CPU_DATA_ALIGN - 1)), %rsp
     call cpu_exc_main
     cpu_ll_exc_leave
 .endm
@@ -201,6 +206,11 @@
     movl %esp, %ebx                         /* save frame */
 .endm
 
+.macro cpu_ll_exc_align_stack nr_args
+    andl $(~(CPU_DATA_ALIGN - 1)), %esp
+    addl $((\nr_args * CPU_WORD_SIZE) % CPU_DATA_ALIGN), %esp
+.endm
+
 .macro cpu_ll_exc_leave
     movl %ebx, %esp                         /* restore stack */
     call thread_schedule                    /* schedule threads */
@@ -210,6 +220,7 @@
 
 .macro cpu_ll_exc_handle vector
     cpu_ll_exc_enter \vector
+    cpu_ll_exc_align_stack 1
     pushl %ebx
     call cpu_exc_main
     cpu_ll_exc_leave
@@ -219,6 +230,7 @@
     cpu_ll_exc_enter \vector
     call cpu_get_intr_stack_ptr
     movl %eax, %esp                         /* switch to interrupt stack */
+    cpu_ll_exc_align_stack 1
     pushl %ebx
     call cpu_intr_main
     cpu_ll_exc_leave