x86: Sanity-check static_cpu_has usage

[deliverable/linux.git] / arch / x86 / include / asm / cpufeature.h

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 043d61e66efc10767c55c3f73e8761016e1ab459..252b28f1176a7cdc84621aeb46ecae092c4cef87 100644 (file)
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -356,15 +356,35 @@ extern const char * const x86_power_flags[32];
 #endif /* CONFIG_X86_64 */
 
 #if __GNUC__ >= 4
+extern void warn_pre_alternatives(void);
+
 /*
  * Static testing of CPU features.  Used the same as boot_cpu_has().
  * These are only valid after alternatives have run, but will statically
  * patch the target code for additional performance.
- *
  */
 static __always_inline __pure bool __static_cpu_has(u16 bit)
 {
 #if __GNUC__ > 4 || __GNUC_MINOR__ >= 5
+
+#ifdef CONFIG_X86_DEBUG_STATIC_CPU_HAS
+               /*
+                * Catch too early usage of this before alternatives
+                * have run.
+                */
+               asm goto("1: jmp %l[t_warn]\n"
+                        "2:\n"
+                        ".section .altinstructions,\"a\"\n"
+                        " .long 1b - .\n"
+                        " .long 0\n"           /* no replacement */
+                        " .word %P0\n"         /* 1: do replace */
+                        " .byte 2b - 1b\n"     /* source len */
+                        " .byte 0\n"           /* replacement len */
+                        ".previous\n"
+                        /* skipping size check since replacement size = 0 */
+                        : : "i" (X86_FEATURE_ALWAYS) : : t_warn);
+#endif
+
                asm goto("1: jmp %l[t_no]\n"
                         "2:\n"
                         ".section .altinstructions,\"a\"\n"
@@ -379,7 +399,13 @@ static __always_inline __pure bool __static_cpu_has(u16 bit)
                return true;
        t_no:
                return false;
-#else
+
+#ifdef CONFIG_X86_DEBUG_STATIC_CPU_HAS
+       t_warn:
+               warn_pre_alternatives();
+               return false;
+#endif
+#else /* GCC_VERSION >= 40500 */
                u8 flag;
                /* Open-coded due to __stringify() in ALTERNATIVE() */
                asm volatile("1: movb $0,%0\n"