[CRIU] [PATCH 3/3] x86: use breakpoints instead of tracing syscalls
Andrey Vagin
avagin at openvz.org
Tue Sep 16 08:00:46 PDT 2014
Currently CRIU traces syscalls to catch a moment, when sigreturn will be
called.
In this patch we set breakpoint on the first instruction after sigreturn
and catch a process in the required moment. It should be much faster.
I was afraid that sigreturn() restarts syscalls and our breakpoints will
not be triggered in this case. But actually sigreturn() always returns
to userspace. Syscalls are restarted by adjusting eip. You can find more
details in get_task_regs().
Signed-off-by: Andrey Vagin <avagin at openvz.org>
---
arch/aarch64/include/asm/parasite-syscall.h | 6 +++
arch/arm/include/asm/parasite-syscall.h | 6 +++
arch/x86/crtools.c | 71 +++++++++++++++++++++++++++++
arch/x86/include/asm/parasite-syscall.h | 2 +
parasite-syscall.c | 5 ++
5 files changed, 90 insertions(+)
diff --git a/arch/aarch64/include/asm/parasite-syscall.h b/arch/aarch64/include/asm/parasite-syscall.h
index 0c07121..5ca586f 100644
--- a/arch/aarch64/include/asm/parasite-syscall.h
+++ b/arch/aarch64/include/asm/parasite-syscall.h
@@ -1,6 +1,8 @@
#ifndef __CR_ASM_PARASITE_SYSCALL_H__
#define __CR_ASM_PARASITE_SYSCALL_H__
+#include <errno.h>
+
struct parasite_ctl;
#define ARCH_SI_TRAP TRAP_BRKPT
@@ -15,4 +17,8 @@ void *mmap_seized(struct parasite_ctl *ctl,
void *addr, size_t length, int prot,
int flags, int fd, off_t offset);
+static inline int parasite_stop_after_sigreturn(pid_t pid, struct parasite_ctl *ctl)
+{
+ return -ENOSYS;
+}
#endif
diff --git a/arch/arm/include/asm/parasite-syscall.h b/arch/arm/include/asm/parasite-syscall.h
index 0c66bf9..4802520 100644
--- a/arch/arm/include/asm/parasite-syscall.h
+++ b/arch/arm/include/asm/parasite-syscall.h
@@ -1,6 +1,7 @@
#ifndef __CR_ASM_PARASITE_SYSCALL_H__
#define __CR_ASM_PARASITE_SYSCALL_H__
+#include <errno.h>
#define ARCH_SI_TRAP TRAP_BRKPT
@@ -15,4 +16,9 @@ void *mmap_seized(struct parasite_ctl *ctl,
void *addr, size_t length, int prot,
int flags, int fd, off_t offset);
+static inline int parasite_stop_after_sigreturn(pid_t pid, struct parasite_ctl *ctl)
+{
+ return -ENOSYS;
+}
+
#endif
diff --git a/arch/x86/crtools.c b/arch/x86/crtools.c
index b127934..916be95 100644
--- a/arch/x86/crtools.c
+++ b/arch/x86/crtools.c
@@ -1,6 +1,8 @@
#include <string.h>
#include <unistd.h>
#include <elf.h>
+#include <sys/user.h>
+#include <sys/wait.h>
#include "asm/processor-flags.h"
#include "asm/restorer.h"
@@ -494,3 +496,72 @@ int sigreturn_prep_fpu_frame(struct rt_sigframe *sigframe, fpu_state_t *fpu_stat
return 0;
}
+/* Copied from the gdb header gdb/nat/x86-dregs.h */
+
+/* Debug registers' indices. */
+#define DR_FIRSTADDR 0
+#define DR_LASTADDR 3
+#define DR_NADDR 4 /* The number of debug address registers. */
+#define DR_STATUS 6 /* Index of debug status register (DR6). */
+#define DR_CONTROL 7 /* Index of debug control register (DR7). */
+
+#define DR_LOCAL_ENABLE_SHIFT 0 /* Extra shift to the local enable bit. */
+#define DR_GLOBAL_ENABLE_SHIFT 1 /* Extra shift to the global enable bit. */
+#define DR_ENABLE_SIZE 2 /* Two enable bits per debug register. */
+
+/* Locally enable the break/watchpoint in the I'th debug register. */
+#define X86_DR_LOCAL_ENABLE(i) (1 << (DR_LOCAL_ENABLE_SHIFT + DR_ENABLE_SIZE * (i)))
+
+int parasite_stop_after_sigreturn(pid_t pid, struct parasite_ctl *ctl)
+{
+ int ret, status;
+
+ /* Set a breakpoint */
+ if (ptrace(PTRACE_POKEUSER, pid,
+ offsetof(struct user, u_debugreg[DR_FIRSTADDR]),
+ RT_SIGFRAME_REGIP(ctl->sigframe))) {
+ pr_err("Unable to setup a breakpoint\n");
+ return 1;
+ }
+
+ /* Clean up the DR_STATUS register */
+ if (ptrace(PTRACE_POKEUSER, pid,
+ offsetof(struct user, u_debugreg[DR_STATUS]), 0)) {
+ pr_err("Unable to setup a breakpoint\n");
+ return 1;
+ }
+
+ /* Enable the breakpoint */
+ if (ptrace(PTRACE_POKEUSER, pid,
+ offsetof(struct user, u_debugreg[DR_CONTROL]),
+ X86_DR_LOCAL_ENABLE(DR_FIRSTADDR))) {
+ pr_err("Unable to setup a breakpoint\n");
+ return 1;
+ }
+ ret = ptrace(PTRACE_CONT, pid, NULL, NULL);
+ if (ret) {
+ pr_perror("ptrace");
+ return -1;
+ }
+
+ pid = wait4(pid, &status, __WALL, NULL);
+ if (pid == -1) {
+ pr_perror("wait4 failed");
+ return -1;
+ }
+
+ if (!WIFSTOPPED(status) || WSTOPSIG(status) != SIGTRAP) {
+ pr_err("Task is in unexpected state: %x\n", status);
+ return -1;
+ }
+
+ /* Disable all breakpoints */
+ if (ptrace(PTRACE_POKEUSER, pid,
+ &((struct user *) NULL)->u_debugreg[DR_CONTROL], 0)) {
+ pr_err("Unable to setup a breakpoint\n");
+ return -1;
+ }
+
+ return 0;
+}
+
diff --git a/arch/x86/include/asm/parasite-syscall.h b/arch/x86/include/asm/parasite-syscall.h
index 4d56cb0..80ca6f1 100644
--- a/arch/x86/include/asm/parasite-syscall.h
+++ b/arch/x86/include/asm/parasite-syscall.h
@@ -17,4 +17,6 @@ void *mmap_seized(struct parasite_ctl *ctl,
void *addr, size_t length, int prot,
int flags, int fd, off_t offset);
+int parasite_stop_after_sigreturn(pid_t pid, struct parasite_ctl *ctl);
+
#endif
diff --git a/parasite-syscall.c b/parasite-syscall.c
index 1c1a2cb..4f0b8e5 100644
--- a/parasite-syscall.c
+++ b/parasite-syscall.c
@@ -868,6 +868,11 @@ static int parasite_fini_seized(struct parasite_ctl *ctl)
if (ret)
return -1;
+ /* CRIU doesn't know how to set breakpoints for this arch */
+ ret = parasite_stop_after_sigreturn(pid, ctl);
+ if (ret != ENOSYS)
+ return ret;
+
ret = ptrace(PTRACE_SYSCALL, pid, NULL, NULL);
if (ret) {
pr_perror("ptrace");
--
1.9.3
More information about the CRIU
mailing list