From: Alan Stern This patch enables the use of abstract debug registers in process-handling routines. [K.Prasad: Split-out from the bigger patch and minor changes following re-basing] Signed-off-by: K.Prasad Signed-off-by: Alan Stern --- arch/x86/kernel/process.c | 23 ++++++----------------- arch/x86/kernel/process_32.c | 31 +++++++++++++++++++++++++++++++ arch/x86/kernel/process_64.c | 33 +++++++++++++++++++++++++++++++++ 3 files changed, 70 insertions(+), 17 deletions(-) Index: arch/x86/kernel/process.c =================================================================== --- arch/x86/kernel/process.c.orig +++ arch/x86/kernel/process.c @@ -16,6 +16,8 @@ #include #include #include +#include +#include unsigned long idle_halt; EXPORT_SYMBOL(idle_halt); @@ -47,6 +49,8 @@ void free_thread_xstate(struct task_stru kmem_cache_free(task_xstate_cachep, tsk->thread.xstate); tsk->thread.xstate = NULL; } + if (unlikely(test_tsk_thread_flag(tsk, TIF_DEBUG))) + flush_thread_hw_breakpoint(tsk); WARN(tsk->thread.ds_ctx, "leaking DS context\n"); } @@ -105,14 +109,9 @@ void flush_thread(void) } #endif - clear_tsk_thread_flag(tsk, TIF_DEBUG); + if (unlikely(test_tsk_thread_flag(tsk, TIF_DEBUG))) + flush_thread_hw_breakpoint(tsk); - tsk->thread.debugreg0 = 0; - tsk->thread.debugreg1 = 0; - tsk->thread.debugreg2 = 0; - tsk->thread.debugreg3 = 0; - tsk->thread.debugreg6 = 0; - tsk->thread.debugreg7 = 0; memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array)); /* * Forget coprocessor state.. @@ -194,16 +193,6 @@ void __switch_to_xtra(struct task_struct else if (next->debugctlmsr != prev->debugctlmsr) update_debugctlmsr(next->debugctlmsr); - if (test_tsk_thread_flag(next_p, TIF_DEBUG)) { - set_debugreg(next->debugreg0, 0); - set_debugreg(next->debugreg1, 1); - set_debugreg(next->debugreg2, 2); - set_debugreg(next->debugreg3, 3); - /* no 4 and 5 */ - set_debugreg(next->debugreg6, 6); - set_debugreg(next->debugreg7, 7); - } - if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^ test_tsk_thread_flag(next_p, TIF_NOTSC)) { /* prev and next are different */ Index: arch/x86/kernel/process_32.c =================================================================== --- arch/x86/kernel/process_32.c.orig +++ arch/x86/kernel/process_32.c @@ -61,6 +61,8 @@ #include #include #include +#include +#include asmlinkage void ret_from_fork(void) __asm__("ret_from_fork"); @@ -265,7 +267,14 @@ int copy_thread(unsigned long clone_flag task_user_gs(p) = get_user_gs(regs); + p->thread.io_bitmap_ptr = NULL; + tsk = current; + err = -ENOMEM; + if (unlikely(test_tsk_thread_flag(tsk, TIF_DEBUG))) + if (copy_thread_hw_breakpoint(tsk, p, clone_flags)) + goto out; + if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) { p->thread.io_bitmap_ptr = kmemdup(tsk->thread.io_bitmap_ptr, IO_BITMAP_BYTES, GFP_KERNEL); @@ -285,10 +294,13 @@ int copy_thread(unsigned long clone_flag err = do_set_thread_area(p, -1, (struct user_desc __user *)childregs->si, 0); +out: if (err && p->thread.io_bitmap_ptr) { kfree(p->thread.io_bitmap_ptr); p->thread.io_bitmap_max = 0; } + if (err) + flush_thread_hw_breakpoint(p); clear_tsk_thread_flag(p, TIF_DS_AREA_MSR); p->thread.ds_ctx = NULL; @@ -427,6 +439,25 @@ __switch_to(struct task_struct *prev_p, lazy_load_gs(next->gs); percpu_write(current_task, next_p); + /* + * There's a problem with moving the arch_install_thread_hw_breakpoint() + * call before current is updated. Suppose a kernel breakpoint is + * triggered in between the two. The hw-breakpoint handler will see + * that current is different from the task pointer stored in + * last_debugged_task, so it will think the task pointer is leftover + * from an old task (lazy switching) and will erase it. Then until the + * next context switch, no user-breakpoints will be installed. + * + * The real problem is that it's impossible to update both current and + * last_debugged_task at the same instant, so there will always be a + * window in which they disagree and a breakpoint might get triggered. + * Since we use lazy switching, we are forced to assume that a + * disagreement means that current is correct and last_debugged_task is + * old. But if you move the code above then you'll create a window in + * which current is old and last_debugged_task is correct. + */ + if (unlikely(test_tsk_thread_flag(next_p, TIF_DEBUG))) + arch_install_thread_hw_breakpoint(next_p); return prev_p; } Index: arch/x86/kernel/process_64.c =================================================================== --- arch/x86/kernel/process_64.c.orig +++ arch/x86/kernel/process_64.c @@ -55,6 +55,8 @@ #include #include #include +#include +#include asmlinkage extern void ret_from_fork(void); @@ -248,6 +250,8 @@ void release_thread(struct task_struct * BUG(); } } + if (unlikely(dead_task->thread.debugreg7)) + flush_thread_hw_breakpoint(dead_task); } static inline void set_32bit_tls(struct task_struct *t, int tls, u32 addr) @@ -303,12 +307,18 @@ int copy_thread(unsigned long clone_flag p->thread.fs = me->thread.fs; p->thread.gs = me->thread.gs; + p->thread.io_bitmap_ptr = NULL; savesegment(gs, p->thread.gsindex); savesegment(fs, p->thread.fsindex); savesegment(es, p->thread.es); savesegment(ds, p->thread.ds); + err = -ENOMEM; + if (unlikely(test_tsk_thread_flag(me, TIF_DEBUG))) + if (copy_thread_hw_breakpoint(me, p, clone_flags)) + goto out; + if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) { p->thread.io_bitmap_ptr = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL); if (!p->thread.io_bitmap_ptr) { @@ -347,6 +357,9 @@ out: kfree(p->thread.io_bitmap_ptr); p->thread.io_bitmap_max = 0; } + if (err) + flush_thread_hw_breakpoint(p); + return err; } @@ -492,6 +505,26 @@ __switch_to(struct task_struct *prev_p, */ if (tsk_used_math(next_p) && next_p->fpu_counter > 5) math_state_restore(); + /* + * There's a problem with moving the arch_install_thread_hw_breakpoint() + * call before current is updated. Suppose a kernel breakpoint is + * triggered in between the two. The hw-breakpoint handler will see + * that current is different from the task pointer stored in + * last_debugged_task, so it will think the task pointer is leftover + * from an old task (lazy switching) and will erase it. Then until the + * next context switch, no user-breakpoints will be installed. + * + * The real problem is that it's impossible to update both current and + * last_debugged_task at the same instant, so there will always be a + * window in which they disagree and a breakpoint might get triggered. + * Since we use lazy switching, we are forced to assume that a + * disagreement means that current is correct and last_debugged_task is + * old. But if you move the code above then you'll create a window in + * which current is old and last_debugged_task is correct. + */ + if (unlikely(test_tsk_thread_flag(next_p, TIF_DEBUG))) + arch_install_thread_hw_breakpoint(next_p); + return prev_p; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/