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authorAndreas Sandberg <andreas@sandberg.pp.se>2013-06-18 16:36:08 +0200
committerAndreas Sandberg <andreas@sandberg.pp.se>2013-06-18 16:36:08 +0200
commitd06064c38613662dfbf68a701052278b4018de8c (patch)
treecc7870da633caf1c52abbd624c37754fe5a99b52
parenta8e8c4f433fb3cce354950ba72136b84abb78015 (diff)
downloadgem5-d06064c38613662dfbf68a701052278b4018de8c.tar.xz
x86: Add support for maintaining the x87 tag word
The current implementation of the x87 never updates the x87 tag word. This is currently not a big issue since the simulated x87 never checks for stack overflows, however this becomes an issue when switching between a virtualized CPU and a simulated CPU. This changeset adds support, which is enabled by default, for updating the tag register to every floating point microop that updates the stack top using the spm mechanism. The new tag words is generated by the helper function X86ISA::genX87Tags(). This function is currently limited to flagging a stack position as valid or invalid and does not try to distinguish between the valid, zero, and special states.
-rw-r--r--src/arch/x86/faults.cc3
-rw-r--r--src/arch/x86/isa/microops/fpop.isa26
-rw-r--r--src/arch/x86/utility.cc20
-rw-r--r--src/arch/x86/utility.hh15
4 files changed, 60 insertions, 4 deletions
diff --git a/src/arch/x86/faults.cc b/src/arch/x86/faults.cc
index 995326562..aa859052e 100644
--- a/src/arch/x86/faults.cc
+++ b/src/arch/x86/faults.cc
@@ -270,6 +270,9 @@ namespace X86ISA
tc->setMiscReg(MISCREG_MXCSR, 0x1f80);
+ // Flag all elements on the x87 stack as empty.
+ tc->setMiscReg(MISCREG_FTW, 0xFFFF);
+
// Update the handy M5 Reg.
tc->setMiscReg(MISCREG_M5_REG, 0);
MicroPC entry = X86ISAInst::RomLabels::extern_label_initIntHalt;
diff --git a/src/arch/x86/isa/microops/fpop.isa b/src/arch/x86/isa/microops/fpop.isa
index 22d6fbcda..142138fb2 100644
--- a/src/arch/x86/isa/microops/fpop.isa
+++ b/src/arch/x86/isa/microops/fpop.isa
@@ -57,6 +57,7 @@ def template MicroFpOpExecute {{
{
%(code)s;
%(flag_code)s;
+ %(tag_code)s;
%(top_code)s;
}
else
@@ -128,11 +129,20 @@ let {{
base = "X86ISA::FpOp"
# Get everything ready for the substitution
+ iop_tag = InstObjParams(name, Name + suffix + "TopTag", base,
+ {"code" : code,
+ "flag_code" : flag_code,
+ "cond_check" : cond_check,
+ "else_code" : else_code,
+ "tag_code" : "FTW = genX87Tags(FTW, TOP, spm);",
+ "top_code" : "TOP = (TOP + spm + 8) % 8;",
+ "op_class" : op_class})
iop_top = InstObjParams(name, Name + suffix + "Top", base,
{"code" : code,
"flag_code" : flag_code,
"cond_check" : cond_check,
"else_code" : else_code,
+ "tag_code" : ";",
"top_code" : "TOP = (TOP + spm + 8) % 8;",
"op_class" : op_class})
iop = InstObjParams(name, Name + suffix, base,
@@ -140,10 +150,14 @@ let {{
"flag_code" : flag_code,
"cond_check" : cond_check,
"else_code" : else_code,
+ "tag_code" : ";",
"top_code" : ";",
"op_class" : op_class})
# Generate the actual code (finally!)
+ header_output += MicroFpOpDeclare.subst(iop_tag)
+ decoder_output += MicroFpOpConstructor.subst(iop_tag)
+ exec_output += MicroFpOpExecute.subst(iop_tag)
header_output += MicroFpOpDeclare.subst(iop_top)
decoder_output += MicroFpOpConstructor.subst(iop_top)
exec_output += MicroFpOpExecute.subst(iop_top)
@@ -191,7 +205,7 @@ let {{
op_class = "FloatAddOp"
def __init__(self, dest, src1, spm=0, \
- SetStatus=False, dataSize="env.dataSize"):
+ SetStatus=False, UpdateFTW=True, dataSize="env.dataSize"):
self.dest = dest
self.src1 = src1
self.src2 = "InstRegIndex(0)"
@@ -201,6 +215,8 @@ let {{
self.className += "Flags"
if spm:
self.className += "Top"
+ if spm and UpdateFTW:
+ self.className += "Tag"
def getAllocator(self, microFlags):
return '''new %(class_name)s(machInst, macrocodeBlock,
@@ -225,7 +241,7 @@ let {{
op_class = "FloatAddOp"
def __init__(self, dest, src1, src2, spm=0, \
- SetStatus=False, dataSize="env.dataSize"):
+ SetStatus=False, UpdateFTW=True, dataSize="env.dataSize"):
self.dest = dest
self.src1 = src1
self.src2 = src2
@@ -235,6 +251,8 @@ let {{
self.className += "Flags"
if spm:
self.className += "Top"
+ if spm and UpdateFTW:
+ self.className += "Tag"
def getAllocator(self, microFlags):
return '''new %(class_name)s(machInst, macrocodeBlock,
@@ -359,10 +377,10 @@ let {{
flag_code = 'FSW = new_fsw;'
class Compfp(FpBinaryOp):
- def __init__(self, src1, src2, spm=0, setStatus=False, \
+ def __init__(self, src1, src2, spm=0, setStatus=False, updateFTW=True, \
dataSize="env.dataSize"):
super(Compfp, self).__init__("InstRegIndex(FLOATREG_MICROFP0)", \
- src1, src2, spm, setStatus, dataSize)
+ src1, src2, spm, setStatus, updateFTW, dataSize)
# This class sets the condition codes in rflags according to the
# rules for comparing floating point.
code = '''
diff --git a/src/arch/x86/utility.cc b/src/arch/x86/utility.cc
index 2398ca073..3df948986 100644
--- a/src/arch/x86/utility.cc
+++ b/src/arch/x86/utility.cc
@@ -268,4 +268,24 @@ setRFlags(ThreadContext *tc, uint64_t val)
tc->setMiscReg(MISCREG_RFLAGS, val & ~(ccFlagMask | cfofMask | DFBit));
}
+uint16_t
+genX87Tags(uint16_t ftw, uint8_t top, int8_t spm)
+{
+ const uint8_t new_top((top + spm + 8) % 8);
+
+ if (spm > 0) {
+ // Removing elements from the stack. Flag the elements as empty.
+ for (int i = top; i != new_top; i = (i + 1 + 8) % 8)
+ ftw |= 0x3 << (2 * i);
+ } else if (spm < 0) {
+ // Adding elements to the stack. Flag the new elements as
+ // valid. We should ideally decode them and "do the right
+ // thing".
+ for (int i = new_top; i != top; i = (i + 1 + 8) % 8)
+ ftw &= ~(0x3 << (2 * i));
+ }
+
+ return ftw;
+}
+
} // namespace X86_ISA
diff --git a/src/arch/x86/utility.hh b/src/arch/x86/utility.hh
index 48840ac77..24aca3e0a 100644
--- a/src/arch/x86/utility.hh
+++ b/src/arch/x86/utility.hh
@@ -141,6 +141,21 @@ namespace X86ISA
inline uint64_t getDoubleBits(double val) {
return *(uint64_t *)(&val);
}
+
+ /**
+ * Generate and updated x87 tag register after a push/pop
+ * operation.
+ *
+ * @note There is currently no support for setting other tags than
+ * valid and invalid. A real x87 will set the tag value to zero or
+ * special for some special floating point values.
+ *
+ * @param ftw Current value of the FTW register.
+ * @param top Current x87 TOP value.
+ * @param spm Stack displacement.
+ * @return New value of the FTW register.
+ */
+ uint16_t genX87Tags(uint16_t ftw, uint8_t top, int8_t spm);
}
#endif // __ARCH_X86_UTILITY_HH__