On Sun, Nov 24, 2019 at 2:31 PM Aleksandar Markovic
<aleksandar.m.m...@gmail.com> wrote:
>
>
>
> On Sunday, November 24, 2019, Helge Deller <del...@gmx.de> wrote:
>>
>> On 24.11.19 13:10, Aleksandar Markovic wrote:
>> >
>> >
>> > On Sunday, November 24, 2019, Helge Deller <del...@gmx.de
>> > <mailto:del...@gmx.de>> wrote:
>> >
>> > On 23.11.19 12:34, Aleksandar Markovic wrote:
>> > > On Thursday, November 21, 2019, Helge Deller <del...@gmx.de
>> > <mailto:del...@gmx.de> <mailto:del...@gmx.de <mailto:del...@gmx.de>>>
>> > wrote:
>> > >
>> > > The strace functionality in qemu-user lacks the possibility to
>> > trace
>> > > which real values get returned to pointers in userspace by
>> > syscalls.
>> > >
>> > > For example, the read() and getcwd() syscalls currently only
>> > show the
>> > > destination address where the syscalls should put the return
>> > values:
>> > > 2532 read(3,0xff80038c,512) = 512
>> > > 2532 getcwd(0x18180,4096) = 9
>> > >
>> > > With the patch below, one now can specify in
>> > print_syscall_late() which
>> > > syscalls should be executed first, before they get printed.
>> > > After adding the read() and getcwd() syscalls, we now get this
>> > output in
>> > > with strace instead:
>> > > 1708
>> > read(3,"\177ELF\1\2\1\3\0\0\0\0\0\0\0\0\0\3\0\17\0\0\0\1\0\2bl\0\0\04"...,512)
>> > = 512
>> > > 1708 getcwd("/usr/bin",4096) = 9
>> > >
>> > > This patch adds just the framework with the respective
>> > implemenations for
>> > > read() and getcwd(). If applied, more functions can be added
>> > easily later.
>> > >
>> > >
>> > > Great out-of-the-box idea! However, there are some things that are
>> > > not thought over yet. There is a good reason why strace happens
>> > > "early": if something crash-like happens during syscall translation,
>> > > we still have trace of original target syscall. In case of "late"
>> > > flavor, we don't have anything. Another potentially problematic
>> > > aspect is that end user certainly should know whether the trace was
>> > > done "early" or "late" - otherwise, there will be, for certain, cases
>> > > of misinterpretation / misleading / confusion of end users.
>> >
>> > Thanks for the feedback - I'm shortly sending a v2 version which
>> > prints the syscall name with an open parenthesis, e.g. "read(" or
>> > "getcwd(",
>> > before calling the syscall. That way you can see where it
>> > crashed/hangs...
>> >
>> >
>> > ... but I cannot see passed arguments (for example, whether NULL is
>> > passed, or somrthing that looks like a real address)...
>>
>> Right.
>> And you won't see that in native strace either...
>> If you have an idea, just let me know.
>>
>
> Helge, I do have an idea how to amend your proposal that should give us,
> believe it or not, "best of both worlds", but let's wait few days, I don't
> have any dev setup ar hand at the moment to check it in action, and on top of
> that I am swamped with other unrelated tasks. In the meantime, maybe other
> guys will say something too, or perhaps you would have something new as well.
>
> Still, by no means, I see this as a (potential) *huge* improvement of QEMU
> strace. Thanks!
>
Helge, Laurent,
I don't have time to experiment, but I will write down here my
suggestion to extending Helge's system in a textual form, based on
example from prevous Helge's patches:
1. CURRENT STATE:
early: read(3,0xff80038c,512)
late: = 512
early: getcwd(0x18180,4096)
late: = 9
2. HELGE'S PROPOSAL 1:
late:
read(3,"\177ELF\1\2\1\3\0\0\0\0\0\0\0\0\0\3\0\17\0\0\0\1\0\2bl\0\0\04"...,512)
= 512
late: getcwd("/usr/bin",4096) = 9
3. HELGE'S PROPOSAL 2:
early: read
late: (3,"\177ELF\1\2\1\3\0\0\0\0\0\0\0\0\0\3\0\17\0\0\0\1\0\2bl\0\0\04"...,512)
= 512
early: getcwd
late: ("/usr/bin",4096) = 9
4. NEW PROPOSAL :
early: read(3,0xff80038c,512)
late: = 512
[(3,"\177ELF\1\2\1\3\0\0\0\0\0\0\0\0\0\3\0\17\0\0\0\1\0\2bl\0\0\04"...,512)]
early: getcwd(0x18180,4096)
late: = 9 [("/usr/bin",4096)]
In other words, we would print for (selected) system calls content of
the parameters both before and after actual ioctl
translation/execution.
Sincerely,
Aleksandar
> Yours,
> Aleksandar
>
>
>>
>> Helge
>>
>> >
>> >
>> >
>> > Helge
>> >
>> > >
>> > > Yours,
>> > > Aleksandar
>> > >
>> > >
>> > >
>> > >
>> > > Signed-off-by: Helge Deller <del...@gmx.de
>> > <mailto:del...@gmx.de> <mailto:del...@gmx.de <mailto:del...@gmx.de>>>
>> > >
>> > > diff --git a/linux-user/strace.c b/linux-user/strace.c
>> > > index de43238fa4..ff254732af 100644
>> > > --- a/linux-user/strace.c
>> > > +++ b/linux-user/strace.c
>> > > @@ -61,6 +61,7 @@ UNUSED static void print_open_flags(abi_long,
>> > int);
>> > > UNUSED static void print_syscall_prologue(const struct
>> > syscallname *);
>> > > UNUSED static void print_syscall_epilogue(const struct
>> > syscallname *);
>> > > UNUSED static void print_string(abi_long, int);
>> > > +UNUSED static void print_encoded_string(abi_long addr, unsigned
>> > int maxlen, int last);
>> > > UNUSED static void print_buf(abi_long addr, abi_long len, int
>> > last);
>> > > UNUSED static void print_raw_param(const char *, abi_long, int);
>> > > UNUSED static void print_timeval(abi_ulong, int);
>> > > @@ -1204,6 +1205,37 @@ print_syscall_epilogue(const struct
>> > syscallname *sc)
>> > > gemu_log(")");
>> > > }
>> > >
>> > > +#define MAX_ENCODED_CHARS 32
>> > > +static void
>> > > +print_encoded_string(abi_long addr, unsigned int maxlen, int
>> > last)
>> > > +{
>> > > + unsigned int maxout;
>> > > + char *s, *str;
>> > > +
>> > > + s = lock_user_string(addr);
>> > > + if (s == NULL) {
>> > > + /* can't get string out of it, so print it as pointer */
>> > > + print_pointer(addr, last);
>> > > + return;
>> > > + }
>> > > +
>> > > + str = s;
>> > > + gemu_log("\"");
>> > > + maxout = MIN(maxlen, MAX_ENCODED_CHARS);
>> > > + while (maxout--) {
>> > > + unsigned char c = *str++;
>> > > + if (isprint(c)) {
>> > > + gemu_log("%c", c);
>> > > + } else {
>> > > + gemu_log("\\%o", (unsigned int) c);
>> > > + }
>> > > + }
>> > > + unlock_user(s, addr, 0);
>> > > +
>> > > + gemu_log("\"%s%s", maxlen > MAX_ENCODED_CHARS ? "..." : "",
>> > > + get_comma(last));
>> > > +}
>> > > +
>> > > static void
>> > > print_string(abi_long addr, int last)
>> > > {
>> > > @@ -1633,6 +1665,19 @@ print_futimesat(const struct syscallname
>> > *name,
>> > > }
>> > > #endif
>> > >
>> > > +#ifdef TARGET_NR_getcwd
>> > > +static void
>> > > +print_getcwd(const struct syscallname *name,
>> > > + abi_long arg0, abi_long arg1, abi_long arg2,
>> > > + abi_long arg3, abi_long arg4, abi_long arg5)
>> > > +{
>> > > + print_syscall_prologue(name);
>> > > + print_string(arg0, 0);
>> > > + print_raw_param("%u", arg1, 1);
>> > > + print_syscall_epilogue(name);
>> > > +}
>> > > +#endif
>> > > +
>> > > #ifdef TARGET_NR_settimeofday
>> > > static void
>> > > print_settimeofday(const struct syscallname *name,
>> > > @@ -2428,6 +2473,20 @@ print_fstatat64(const struct syscallname
>> > *name,
>> > > #define print_newfstatat print_fstatat64
>> > > #endif
>> > >
>> > > +#ifdef TARGET_NR_read
>> > > +static void
>> > > +print_read(const struct syscallname *name,
>> > > + abi_long arg0, abi_long arg1, abi_long arg2,
>> > > + abi_long arg3, abi_long arg4, abi_long arg5)
>> > > +{
>> > > + print_syscall_prologue(name);
>> > > + print_raw_param("%d", arg0, 0);
>> > > + print_encoded_string(arg1, arg2, 0);
>> > > + print_raw_param("%u", arg2, 1);
>> > > + print_syscall_epilogue(name);
>> > > +}
>> > > +#endif
>> > > +
>> > > #ifdef TARGET_NR_readlink
>> > > static void
>> > > print_readlink(const struct syscallname *name,
>> > > diff --git a/linux-user/strace.list b/linux-user/strace.list
>> > > index d49a1e92a8..220b1f4c46 100644
>> > > --- a/linux-user/strace.list
>> > > +++ b/linux-user/strace.list
>> > > @@ -272,7 +272,7 @@
>> > > { TARGET_NR_getcpu, "getcpu" , "%s(%p,%d)", NULL, NULL },
>> > > #endif
>> > > #ifdef TARGET_NR_getcwd
>> > > -{ TARGET_NR_getcwd, "getcwd" , "%s(%p,%d)", NULL, NULL },
>> > > +{ TARGET_NR_getcwd, "getcwd" , NULL, print_getcwd, NULL },
>> > > #endif
>> > > #ifdef TARGET_NR_getdents
>> > > { TARGET_NR_getdents, "getdents" , NULL, NULL, NULL },
>> > > @@ -1080,7 +1080,7 @@
>> > > { TARGET_NR_quotactl, "quotactl" , NULL, NULL, NULL },
>> > > #endif
>> > > #ifdef TARGET_NR_read
>> > > -{ TARGET_NR_read, "read" , "%s(%d,%#x,%d)", NULL, NULL },
>> > > +{ TARGET_NR_read, "read" , NULL, print_read, NULL },
>> > > #endif
>> > > #ifdef TARGET_NR_readahead
>> > > { TARGET_NR_readahead, "readahead" , NULL, NULL, NULL },
>> > > diff --git a/linux-user/syscall.c b/linux-user/syscall.c
>> > > index ce399a55f0..c0079ca2b7 100644
>> > > --- a/linux-user/syscall.c
>> > > +++ b/linux-user/syscall.c
>> > > @@ -12069,6 +12069,21 @@ static abi_long do_syscall1(void
>> > *cpu_env, int num, abi_long arg1,
>> > > return ret;
>> > > }
>> > >
>> > > +/*
>> > > + * True if this syscall should be printed after having called
>> > the native
>> > > + * syscall, so that values which are fed back to userspace gets
>> > printed.
>> > > + */
>> > > +static int print_syscall_late(int syscall)
>> > > +{
>> > > + switch (syscall) {
>> > > + case TARGET_NR_getcwd:
>> > > + case TARGET_NR_read:
>> > > + return 1;
>> > > + default:
>> > > + return 0;
>> > > + }
>> > > +}
>> > > +
>> > > abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
>> > > abi_long arg2, abi_long arg3, abi_long arg4,
>> > > abi_long arg5, abi_long arg6, abi_long arg7,
>> > > @@ -12095,9 +12110,16 @@ abi_long do_syscall(void *cpu_env, int
>> > num, abi_long arg1,
>> > > arg2, arg3, arg4, arg5, arg6, arg7,
>> > arg8);
>> > >
>> > > if (unlikely(do_strace)) {
>> > > - print_syscall(num, arg1, arg2, arg3, arg4, arg5, arg6);
>> > > + int late_printing;
>> > > + late_printing = print_syscall_late(num);
>> > > + if (!late_printing) {
>> > > + print_syscall(num, arg1, arg2, arg3, arg4, arg5,
>> > arg6);
>> > > + }
>> > > ret = do_syscall1(cpu_env, num, arg1, arg2, arg3, arg4,
>> > > arg5, arg6, arg7, arg8);
>> > > + if (late_printing) {
>> > > + print_syscall(num, arg1, arg2, arg3, arg4, arg5,
>> > arg6);
>> > > + }
>> > > print_syscall_ret(num, ret);
>> > > } else {
>> > > ret = do_syscall1(cpu_env, num, arg1, arg2, arg3, arg4,
>> > >
>> >
>>
