[Git][cmucl/cmucl][issue-86-save-fpu-state-on-entry-to-alloc] Save FPU state in alloc_overflow_sse2

[Raymond Toy]

Raymond Toy pushed to branch issue-86-save-fpu-state-on-entry-to-alloc at cmucl / cmucl


Commits:
8b08b800 by Raymond Toy at 2020-08-27T20:39:07-07:00
Save FPU state in alloc_overflow_sse2

It's best to save the FPU state here instead of in alloc() because we
can't know what the compiler might do.  Remove the fpu save stuff from
alloc().

gcc 9.3.1 builds lisp successfully.

- - - - -


2 changed files:

- src/lisp/gencgc.c
- src/lisp/x86-assem.S


Changes:

=====================================
src/lisp/gencgc.c
=====================================
@@ -8412,28 +8412,11 @@ gencgc_pickup_dynamic(void)
 
 void do_pending_interrupt(void);
 
-//#pragma GCC optimize ("-O1")
 char *
 alloc(int nbytes)
 {
-#if (defined(i386) || defined(__x86_64))
-    /*
-     * Need to save and restore the FPU registers on x86, but only for
-     * sse2.  See Trac ticket #61
-     * (https://trac.common-lisp.net/cmucl/ticket/61) and gitlab
-     * ticket #86
-     * (https://gitlab.common-lisp.net/cmucl/cmucl/-/issues/86).
-     *
-     * Not needed by sparc or ppc because we never call alloc from
-     * Lisp directly to do allocation.
-     */
-    FPU_STATE(fpu_state);
-
-    if (fpu_mode == SSE2) {
-        save_fpu_state(fpu_state);
-    }
-#endif
     void *new_obj;
+
 #if !(defined(sparc) || (defined(DARWIN) && defined(__ppc__)))
     /*
      * *current-region-free-pointer* is the same as alloc-tn (=
@@ -8483,14 +8466,8 @@ alloc(int nbytes)
 	}
     }
 
-#if (defined(i386) || defined(__x86_64))
-    if (fpu_mode == SSE2) {
-        restore_fpu_state(fpu_state);
-    }
-#endif
     return new_obj;
 }
-#pragma GCC optimize ("-O2")
 
 char *
 alloc_pseudo_atomic(int nbytes)


=====================================
src/lisp/x86-assem.S
=====================================
@@ -381,6 +381,7 @@ ENDFUNC(fastcopy16)
  * On exit:
  * %eax = address
  */
+#if 0
 FUNCDEF(alloc_overflow_sse2)
 	STACK_PROLOGUE(20)
 	movl	%ecx, 8(%esp)	# Save ecx and edx registers
@@ -401,7 +402,49 @@ FUNCDEF(alloc_overflow_sse2)
 	STACK_EPILOGUE
 	ret
 ENDFUNC(alloc_overflow_sse2)	
-		
+#else
+FUNCDEF(alloc_overflow_sse2)
+	# Need 512 bytes for the fpu save area, space to save ecx and edx, 
+	# space for mxcsr, a temp, and one arg to pass to alloc.  That's 
+	# 512 + 20.  But the save area needs to be 16-byte aligned, so
+	# allocate 512 + 32 bytes.  The fpu area will be at offset 32.
+	#
+	# Stack looks like:
+	#
+	#      +544 -> end
+	#      +32  -> fpu save
+        #      +20  -> unused
+	#      +16  -> temp
+	#      +12  -> mxcsr
+	#      + 8  -> save ecx
+	#      + 4  -> save edx
+	#  esp + 0  -> arg for alloc
+	STACK_PROLOGUE(32+512)
+	movl	%ecx, 8(%esp)	# Save ecx and edx registers
+	movl	%edx, 4(%esp)
+	stmxcsr 12(%esp)	# Save MXCSR
+	/* Clear the exceptions that might have occurred */
+	movl	12(%esp), %edx
+	and	$-64, %edx	# Clear the exceptions
+	movl	%edx, 16(%esp)
+	ldmxcsr 16(%esp)	# Get new mxcsr value
+	movl	%eax, (%esp)	# Put size on stack for first arg to alloc()
+
+	# Save all FPU regs because we don't know what's in use by lisp.
+	fxsave	32(%esp)
+	
+	call	GNAME(alloc)
+
+	fxrstor 32(%esp)
+
+	movl	4(%esp), %edx	# Restore edx and ecx registers.  eax has the return value.
+	movl	8(%esp), %ecx
+	ldmxcsr	12(%esp)
+	STACK_EPILOGUE
+	ret
+ENDFUNC(alloc_overflow_sse2)	
+#endif		
+
 #ifdef LINKAGE_TABLE
 
 /* Call into C code to resolve a linkage entry.  The initial code in the 



View it on GitLab: https://gitlab.common-lisp.net/cmucl/cmucl/-/commit/8b08b800dc1c26d498fbc4054980c8d8bd761fe4

-- 
View it on GitLab: https://gitlab.common-lisp.net/cmucl/cmucl/-/commit/8b08b800dc1c26d498fbc4054980c8d8bd761fe4
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