[CRIU] [PATCH 3/3] x86: use breakpoints instead of tracing syscalls
Andrew Vagin
avagin at parallels.com
Tue Sep 16 08:15:37 PDT 2014
On Tue, Sep 16, 2014 at 07:00:46PM +0400, Andrey Vagin wrote:
> 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().
I forgot that we can start handle signals after sigreturn. I will send a
fixed version tomorrow. Your comments are welcome.
>
> 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
>
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