2 files changed, 77 insertions, 0 deletions

diff --git a/src/arch/x86/utility.cc b/src/arch/x86/utility.cc
index 3df948986..7f5ae980a 100644
--- a/src/arch/x86/utility.cc
+++ b/src/arch/x86/utility.cc
@@ -268,6 +268,52 @@ setRFlags(ThreadContext *tc, uint64_t val)
     tc->setMiscReg(MISCREG_RFLAGS, val & ~(ccFlagMask | cfofMask | DFBit));
 }
 
+uint8_t
+convX87TagsToXTags(uint16_t ftw)
+{
+    uint8_t ftwx(0);
+    for (int i = 0; i < 8; ++i) {
+        // Extract the tag for the current element on the FP stack
+        const unsigned tag((ftw >> (2 * i)) & 0x3);
+
+        /*
+         * Check the type of the current FP element. Valid values are:
+         * 0 == Valid
+         * 1 == Zero
+         * 2 == Special (Nan, unsupported, infinity, denormal)
+         * 3 == Empty
+         */
+        // The xsave version of the tag word only keeps track of
+        // whether the element is empty or not. Set the corresponding
+        // bit in the ftwx if it's not empty,
+        if (tag != 0x3)
+            ftwx |= 1 << i;
+    }
+
+    return ftwx;
+}
+
+uint16_t
+convX87XTagsToTags(uint8_t ftwx)
+{
+    uint16_t ftw(0);
+    for (int i = 0; i < 8; ++i) {
+        const unsigned xtag(((ftwx >> i) & 0x1));
+
+        // The xtag for an x87 stack position is 0 for empty stack positions.
+        if (!xtag) {
+            // Set the tag word to 3 (empty) for the current element.
+            ftw |= 0x3 << (2 * i);
+        } else {
+            // TODO: We currently assume that non-empty elements are
+            // valid (0x0), but we should ideally reconstruct the full
+            // state (valid/zero/special).
+        }
+    }
+
+    return ftw;
+}
+
 uint16_t
 genX87Tags(uint16_t ftw, uint8_t top, int8_t spm)
 {
diff --git a/src/arch/x86/utility.hh b/src/arch/x86/utility.hh
index 24aca3e0a..dcf61bddb 100644
--- a/src/arch/x86/utility.hh
+++ b/src/arch/x86/utility.hh
@@ -143,6 +143,37 @@ namespace X86ISA
     }
 
     /**
+     * Convert an x87 tag word to abridged tag format.
+     *
+     * Convert from the x87 tag representation to the tag abridged
+     * representation used in the FXSAVE area. The classic format uses
+     * 2 bits per stack position to indicate if a position is valid,
+     * zero, special, or empty. The abridged format only stores
+     * whether a position is empty or not.
+     *
+     * @param ftw Tag word in classic x87 format.
+     * @return Tag word in the abridged format.
+     */
+    uint8_t convX87TagsToXTags(uint16_t ftw);
+
+    /**
+     * Convert an x87 xtag word to normal tags format.
+     *
+     * Convert from the abridged x87 tag representation used in the
+     * FXSAVE area to a full x87 tag. The classic format uses 2 bits
+     * per stack position to indicate if a position is valid, zero,
+     * special, or empty. The abridged format only stores whether a
+     * position is empty or not.
+     *
+     * @todo Reconstruct the correct state of stack positions instead
+     * of just valid/invalid.
+     *
+     * @param ftwx Tag word in the abridged format.
+     * @return Tag word in classic x87 format.
+     */
+    uint16_t convX87XTagsToTags(uint8_t ftwx);
+
+    /**
      * Generate and updated x87 tag register after a push/pop
      * operation.
      *