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Subject[PATCH 3/7] uml: clean arch_switch usage
Date
From: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>

Call arch_switch also in switch_to_skas, even if it's, for now, a no-op for that
case (and mark this in the comment); this will change soon.

Also, arch_switch for TT mode is actually useless when the PT proxy (a
complicate debugging instrumentation for TT mode) is not enabled. In fact, it
only calls update_debugregs, which checks debugregs_seq against seq (to check
if the registers are up-to-date - seq here means a "version number" of the
registers).

If the ptrace proxy is not enabled, debugregs_seq always stays 0 and
update_debugregs will be a no-op. So, optimize this out (the compiler can't
do it).

Also, I've been disappointed by the fact that it would make a lot of sense
if, after calling a successful
update_debugregs(current->thread.arch.debugregs_seq),
current->thread.arch.debugregs_seq were updated with the new debugregs_seq.
But this is not done. Is this a bug or a feature? For all purposes, it seems
a bug (otherwise the whole mechanism does not make sense, which is also a
possibility to check), which causes some performance only problems (not
correctness), since we write_debugregs when not needed.

Also, as suggested by Jeff, remove a redundant enabling of SIGVTALRM,
comprised in the subsequent local_irq_enable(). I'm just a bit dubious if
ordering matters there...

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
---

arch/um/include/kern_util.h | 6 +++++-
arch/um/include/sysdep-i386/ptrace.h | 5 +++++
arch/um/kernel/skas/process_kern.c | 2 ++
arch/um/kernel/tt/process_kern.c | 10 ++++++++--
arch/um/sys-i386/ptrace.c | 8 ++++++--
arch/um/sys-i386/ptrace_user.c | 10 +++++++++-
6 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/arch/um/include/kern_util.h b/arch/um/include/kern_util.h
index 07176d9..4255713 100644
--- a/arch/um/include/kern_util.h
+++ b/arch/um/include/kern_util.h
@@ -116,7 +116,11 @@ extern void *get_current(void);
extern struct task_struct *get_task(int pid, int require);
extern void machine_halt(void);
extern int is_syscall(unsigned long addr);
-extern void arch_switch(void);
+
+extern void arch_switch_to_tt(struct task_struct *from, struct task_struct *to);
+
+extern void arch_switch_to_skas(struct task_struct *from, struct task_struct *to);
+
extern void free_irq(unsigned int, void *);
extern int cpu(void);

diff --git a/arch/um/include/sysdep-i386/ptrace.h b/arch/um/include/sysdep-i386/ptrace.h
index c8ee955..6670cc9 100644
--- a/arch/um/include/sysdep-i386/ptrace.h
+++ b/arch/um/include/sysdep-i386/ptrace.h
@@ -14,7 +14,12 @@
#define MAX_REG_NR (UM_FRAME_SIZE / sizeof(unsigned long))
#define MAX_REG_OFFSET (UM_FRAME_SIZE)

+#ifdef UML_CONFIG_PT_PROXY
extern void update_debugregs(int seq);
+#else
+static inline void update_debugregs(int seq) {}
+#endif
+

/* syscall emulation path in ptrace */

diff --git a/arch/um/kernel/skas/process_kern.c b/arch/um/kernel/skas/process_kern.c
index 3f70a2e..14360ac 100644
--- a/arch/um/kernel/skas/process_kern.c
+++ b/arch/um/kernel/skas/process_kern.c
@@ -35,6 +35,8 @@ void switch_to_skas(void *prev, void *ne
switch_threads(&from->thread.mode.skas.switch_buf,
to->thread.mode.skas.switch_buf);

+ arch_switch_to_skas(current->thread.prev_sched, current);
+
if(current->pid == 0)
switch_timers(1);
}
diff --git a/arch/um/kernel/tt/process_kern.c b/arch/um/kernel/tt/process_kern.c
index 295c1ac..a9c1443 100644
--- a/arch/um/kernel/tt/process_kern.c
+++ b/arch/um/kernel/tt/process_kern.c
@@ -51,6 +51,13 @@ void switch_to_tt(void *prev, void *next

c = 0;

+ /* Notice that here we "up" the semaphore on which "to" is waiting, and
+ * below (the read) we wait on this semaphore (which is implemented by
+ * switch_pipe) and go sleeping. Thus, after that, we have resumed in
+ * "to", and can't use any more the value of "from" (which is outdated),
+ * nor the value in "to" (since it was the task which stole us the CPU,
+ * which we don't care about). */
+
err = os_write_file(to->thread.mode.tt.switch_pipe[1], &c, sizeof(c));
if(err != sizeof(c))
panic("write of switch_pipe failed, err = %d", -err);
@@ -77,7 +84,7 @@ void switch_to_tt(void *prev, void *next
change_sig(SIGALRM, alrm);
change_sig(SIGPROF, prof);

- arch_switch();
+ arch_switch_to_tt(prev_sched, current);

flush_tlb_all();
local_irq_restore(flags);
@@ -141,7 +148,6 @@ static void new_thread_handler(int sig)
set_cmdline("(kernel thread)");

change_sig(SIGUSR1, 1);
- change_sig(SIGVTALRM, 1);
change_sig(SIGPROF, 1);
local_irq_enable();
if(!run_kernel_thread(fn, arg, &current->thread.exec_buf))
diff --git a/arch/um/sys-i386/ptrace.c b/arch/um/sys-i386/ptrace.c
index 8032a10..bf896b8 100644
--- a/arch/um/sys-i386/ptrace.c
+++ b/arch/um/sys-i386/ptrace.c
@@ -15,9 +15,13 @@
#include "sysdep/sigcontext.h"
#include "sysdep/sc.h"

-void arch_switch(void)
+void arch_switch_to_tt(struct task_struct *from, struct task_struct *to)
+{
+ update_debugregs(to->thread.arch.debugregs_seq);
+}
+
+void arch_switch_to_skas(struct task_struct *from, struct task_struct *to)
{
- update_debugregs(current->thread.arch.debugregs_seq);
}

int is_syscall(unsigned long addr)
diff --git a/arch/um/sys-i386/ptrace_user.c b/arch/um/sys-i386/ptrace_user.c
index 397e3c3..e6826ef 100644
--- a/arch/um/sys-i386/ptrace_user.c
+++ b/arch/um/sys-i386/ptrace_user.c
@@ -14,6 +14,7 @@
#include "sysdep/thread.h"
#include "user.h"
#include "os.h"
+#include "uml-config.h"

int ptrace_getregs(long pid, unsigned long *regs_out)
{
@@ -43,6 +44,7 @@ int ptrace_setfpregs(long pid, unsigned
return 0;
}

+/* All the below stuff is of interest for TT mode only */
static void write_debugregs(int pid, unsigned long *regs)
{
struct user *dummy;
@@ -75,7 +77,6 @@ static void read_debugregs(int pid, unsi

/* Accessed only by the tracing thread */
static unsigned long kernel_debugregs[8] = { [ 0 ... 7 ] = 0 };
-static int debugregs_seq = 0;

void arch_enter_kernel(void *task, int pid)
{
@@ -89,6 +90,11 @@ void arch_leave_kernel(void *task, int p
write_debugregs(pid, TASK_DEBUGREGS(task));
}

+#ifdef UML_CONFIG_PT_PROXY
+/* Accessed only by the tracing thread */
+static int debugregs_seq = 0;
+
+/* Only called by the ptrace proxy */
void ptrace_pokeuser(unsigned long addr, unsigned long data)
{
if((addr < offsetof(struct user, u_debugreg[0])) ||
@@ -109,6 +115,7 @@ static void update_debugregs_cb(void *ar
write_debugregs(pid, kernel_debugregs);
}

+/* Optimized out in its header when not defined */
void update_debugregs(int seq)
{
int me;
@@ -118,6 +125,7 @@ void update_debugregs(int seq)
me = os_getpid();
initial_thread_cb(update_debugregs_cb, &me);
}
+#endif

/*
* Overrides for Emacs so that we follow Linus's tabbing style.
-
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