arch/x86_64: Flag xuk shared page volatile

The shared page is inherently used in multiprocessor contexts where the compiler optimizer can trip us up (specifically, a spin on num_active_pus was being hoisted out of the loop on some gcc's). Put the volatile declartion into the struct pointer itself instead of relying on the code to get it right. Signed-off-by: Andy Ross <[email protected]>
dagar · Mar 13, 2019 · bbe6fa0 · bbe6fa0
1 parent 1781ec9
commit bbe6fa0
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Showing 2 changed files with 3 additions and 3 deletions.
diff --git a/arch/x86_64/core/shared-page.h b/arch/x86_64/core/shared-page.h
@@ -57,7 +57,7 @@ struct xuk_shared_mem {
 	int vgacol;
 };
 
-#define _shared (*((struct xuk_shared_mem *)(long)SHARED_ADDR))
+#define _shared (*((volatile struct xuk_shared_mem *)(long)SHARED_ADDR))
 
 static inline void shared_init(void)
 {

diff --git a/arch/x86_64/core/xuk.c b/arch/x86_64/core/xuk.c
@@ -314,8 +314,8 @@ void xuk_set_isr_mask(int interrupt, int masked)
 static void setup_fg_segs(int cpu)
 {
 	int fi = 3 + 2 * cpu, gi = 3 + 2 * cpu + 1;
-	struct gdt64 *fs = &_shared.gdt[fi];
-	struct gdt64 *gs = &_shared.gdt[gi];
+	struct gdt64 *fs = (struct gdt64 *) &_shared.gdt[fi];
+	struct gdt64 *gs = (struct gdt64 *) &_shared.gdt[gi];
 
 	gdt64_set_base(fs, (long)&_shared.fs_ptrs[cpu]);
 	gdt64_set_base(gs, (long)&_shared.gs_ptrs[cpu]);