x86: Debugger can now use dr3

headers/private/kernel/arch/x86/arch_thread.h

@@ -62,7 +62,7 @@ void arch_syscall_64_bit_return_value(void);
 static inline void
 arch_thread_set_current_thread(Thread* t)
 {
-	asm volatile("mov %0, %%gs:0" : : "r" (t));
+	asm volatile("mov %0, %%gs:0" : : "r" (t) : "memory");
 }
 
 

headers/private/kernel/arch/x86/arch_user_debugger.h

@@ -9,12 +9,7 @@
 #define ARCH_INIT_USER_DEBUG x86_init_user_debug
 
 // number of breakpoints the CPU supports
-// On 32-bit, DR3 is used to hold the Thread*.
+#define X86_BREAKPOINT_COUNT		4
-#ifdef __x86_64__
-#	define X86_BREAKPOINT_COUNT		4
-#else
-#	define X86_BREAKPOINT_COUNT		3
-#endif
 
 // debug status register DR6
 enum {

src/system/kernel/arch/x86/arch_debug.cpp

@@ -1202,13 +1202,13 @@ arch_debug_get_interrupt_pc(bool* _isSyscall)
 void
 arch_debug_unset_current_thread(void)
 {
-#ifdef __x86_64__
 	// Can't just write 0 to the GS base, that will cause the read from %gs:0
 	// to fault. Instead point it at a NULL pointer, %gs:0 will get this value.
 	static Thread* unsetThread = NULL;
+#ifdef __x86_64__
 	x86_write_msr(IA32_MSR_GS_BASE, (addr_t)&unsetThread);
 #else
-	x86_write_dr3(NULL);
+	asm volatile("mov %0, %%gs:0" : : "r" (unsetThread) : "memory");
 #endif
 }
 

src/system/kernel/arch/x86/arch_user_debugger.cpp

@@ -201,10 +201,7 @@ install_breakpoints(const arch_team_debug_info& teamInfo)
 	asm("mov %0, %%dr0" : : "r"(teamInfo.breakpoints[0].address));
 	asm("mov %0, %%dr1" : : "r"(teamInfo.breakpoints[1].address));
 	asm("mov %0, %%dr2" : : "r"(teamInfo.breakpoints[2].address));
-#ifdef __x86_64__
 	asm("mov %0, %%dr3" : : "r"(teamInfo.breakpoints[3].address));
-		// DR3 is used to hold the current Thread* on 32.
-#endif
 
 	// enable breakpoints
 	asm("mov %0, %%dr7" : : "r"(teamInfo.dr7));