Stackless issue #183: use a volatile pointer to call slp_switch()

Prevent inlining slp_switch() more reliably. C standard guarantees to read the value of a volatile variable from memory on each access. Therefore the compiler does not know the called function and can't inline. (cherry picked from commit 78f6b66)
stackless-dev · Nov 12, 2018 · ae7db35 · ae7db35
1 parent a8cf08d
commit ae7db35
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Showing 9 changed files with 13 additions and 73 deletions.
diff --git a/Stackless/core/slp_transfer.c b/Stackless/core/slp_transfer.c
@@ -117,6 +117,10 @@ slp_transfer(PyCStackObject **cstprev, PyCStackObject *cst,
 {
     PyThreadState *ts = PyThreadState_GET();
     int result;
+    /* Use a volatile pointer to prevent inlining of slp_switch().
+     * See Stackless issue 183
+     */
+    static int (*volatile slp_switch_ptr)(void) = slp_switch;
 
     /* since we change the stack we must assure that the protocol was met */
     STACKLESS_ASSERT();
@@ -148,7 +152,7 @@ slp_transfer(PyCStackObject **cstprev, PyCStackObject *cst,
     _cstprev = cstprev;
     _cst = cst;
     _prev = prev;
-    result = slp_switch();
+    result = slp_switch_ptr();
     SLP_ASSERT_FRAME_IN_TRANSFER(ts);
     if (!result) {
         if (_cst) {

diff --git a/Stackless/platf/switch_amd64_unix.h b/Stackless/platf/switch_amd64_unix.h
@@ -94,15 +94,7 @@
     "xmm8", "xmm9", "xmm10", "xmm11", "xmm12", "xmm13", "xmm14", "xmm15"
 #endif
 
-/* 
- * You may want to make the function static enable optimizations.
- * However, the ABI SPEC does not apply to static functions. Therefore 
- * I make slp_switch a regular global function.
- */
-#if 0
-static
-#endif
-int
+static int
 slp_switch(void)
 {
     register long *stackref, stsizediff;

diff --git a/Stackless/platf/switch_arm32_gcc.h b/Stackless/platf/switch_arm32_gcc.h
@@ -27,15 +27,7 @@
 #define STACK_MAGIC 0
 #define REGS_TO_SAVE /*"r1", "r2", "r3", "r4",*/ "r5", "r6", "fp", "ip", "lr"
 
-/*
- * You may want to make the function static enable optimizations.
- * However, the ABI SPEC does not apply to static functions. Therefore
- * I make slp_switch a regular global function.
- */
-#if 0
-static
-#endif
-int
+static int
 slp_switch(void)
 {
     register int *stackref, stsizediff;

diff --git a/Stackless/platf/switch_mips_unix.h b/Stackless/platf/switch_mips_unix.h
@@ -20,15 +20,7 @@
        "$23", "$30"
 #endif
     __asm__ volatile ("" : : : REGS_TO_SAVE);
-/*
- * You may want to make the function static enable optimizations.
- * However, the ABI SPEC does not apply to static functions. Therefore
- * I make slp_switch a regular global function.
- */
-#if 0
-static
-#endif
-int
+static int
 slp_switch(void)
 {
     register int *stackref, stsizediff;

diff --git a/Stackless/platf/switch_ppc_macosx.h b/Stackless/platf/switch_ppc_macosx.h
@@ -42,15 +42,7 @@
        "cr2", "cr3", "cr4"
 #endif
 
-/*
- * You may want to make the function static enable optimizations.
- * However, the ABI SPEC does not apply to static functions. Therefore
- * I make slp_switch a regular global function.
- */
-#if 0
-static
-#endif
-int
+static int
 slp_switch(void)
 {
     static int x = 0;

diff --git a/Stackless/platf/switch_ppc_unix.h b/Stackless/platf/switch_ppc_unix.h
@@ -37,15 +37,7 @@
 #define REGS_TO_SAVE "r13", "r14", "r15", "r16", "r17", "r18", "r19", "r20", \
        "r21", "r22", "r23", "r24", "r25", "r26", "r27", "r28", "r29", "r31", \
        "cr2", "cr3", "cr4"
-/*
- * You may want to make the function static enable optimizations.
- * However, the ABI SPEC does not apply to static functions. Therefore
- * I make slp_switch a regular global function.
- */
-#if 0
-static
-#endif
-int
+static int
 slp_switch(void)
 {
     register int *stackref, stsizediff;

diff --git a/Stackless/platf/switch_s390_unix.h b/Stackless/platf/switch_s390_unix.h
@@ -21,15 +21,7 @@
              "f0", "f1", "f2", "f3", "f4", "f5", "f6", "f7", \
              "f8", "f9", "f10", "f11", "f12", "f13", "f14", "f15"
 
-/*
- * You may want to make the function static enable optimizations.
- * However, the ABI SPEC does not apply to static functions. Therefore
- * I make slp_switch a regular global function.
- */
-#if 0
-static
-#endif
-int
+static int
 slp_switch(void)
 {
     register int *stackref, stsizediff;

diff --git a/Stackless/platf/switch_sparc_sun_gcc.h b/Stackless/platf/switch_sparc_sun_gcc.h
@@ -23,15 +23,7 @@
 
 #define STACK_MAGIC 0
 
-/*
- * You may want to make the function static enable optimizations.
- * However, the ABI SPEC does not apply to static functions. Therefore
- * I make slp_switch a regular global function.
- */
-#if 0
-static
-#endif
-int
+static int
 slp_switch(void)
 {
     register int *stackref, stsizediff;

diff --git a/Stackless/platf/switch_x86_unix.h b/Stackless/platf/switch_x86_unix.h
@@ -66,15 +66,7 @@
 /* Registers marked as clobbered, minimum set according to the ABI spec. */
 #define REGS_CLOBBERED "ebx", "edi", "esi"
 
-/*
- * You may want to make the function static enable optimizations.
- * However, the ABI SPEC does not apply to static functions. Therefore
- * I make slp_switch a regular global function.
- */
-#if 0
-static
-#endif
-int
+static int
 slp_switch(void)
 {
     register int *stackref, stsizediff;