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From: Thomas M. <th...@m3...> - 2017-06-20 01:56:58
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Hi,
I finally did figure out where in the host kernel the ptrace syscall
fails with -EFAULT.
In arch/x86/kernel/fpu/regset.c:130:
114 int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
115 unsigned int pos, unsigned int count,
116 const void *kbuf, const void __user *ubuf)
117 {
118 struct fpu *fpu = &target->thread.fpu;
119 struct xregs_state *xsave;
120 int ret;
121
122 if (!boot_cpu_has(X86_FEATURE_XSAVE))
123 return -ENODEV;
124
125 pr_info("in xstateregs_set");
126
127 /*
128 * A whole standard-format XSAVE buffer is needed:
129 */
130 if ((pos != 0) || (count < fpu_user_xstate_size)) {
131 pr_info("EFAULT from xstateregs_set");
132-> pr_info("pos = %i, count = %i, fpu_user_xstate_size= %i\n", pos, count, fpu_user_xstate_size);
133 return -EFAULT;
134 }
Sadly I had to fallback to debugging by printk because kgdb/qemu
gdbstub, all didn't work for some unknown reason :-(
output is:
[ 69.598349] EFAULT from xstateregs_set
[ 69.598350] pos = 0, count = 832, fpu_user_xstate_size= 1088
calling code is in arch/x86/um/os-Linux/registers.c:
49 int restore_fp_registers(int pid, unsigned long *fp_regs)
50 {
51 struct iovec iov;
52
53 if (have_xstate_support) {
54 iov.iov_base = fp_regs;
55 iov.iov_len = sizeof(struct _xstate);
56 if (ptrace(PTRACE_SETREGSET, pid, NT_X86_XSTATE, &iov) < 0)
57 -> return -errno;
58 return 0;
59 } else {
60 return restore_i387_registers(pid, fp_regs);
61 }
62 }
it looks like _xstate is too short for above operation, I wonder why
PTRACE_GETREGSET works without a warning of too short size.
with kind regards
thomas
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From: Richard W. <ri...@no...> - 2017-06-20 06:58:28
|
Thomas,
Am 20.06.2017 um 03:56 schrieb Thomas Meyer:
> Hi,
>
> I finally did figure out where in the host kernel the ptrace syscall
> fails with -EFAULT.
Nice! Thanks a lot for digging into this. I still had no chance to setup
Ipv6 to connect to your host and figure myself. ;-\
> In arch/x86/kernel/fpu/regset.c:130:
>
> 114 int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
> 115 unsigned int pos, unsigned int count,
> 116 const void *kbuf, const void __user *ubuf)
> 117 {
> 118 struct fpu *fpu = &target->thread.fpu;
> 119 struct xregs_state *xsave;
> 120 int ret;
> 121
> 122 if (!boot_cpu_has(X86_FEATURE_XSAVE))
> 123 return -ENODEV;
> 124
> 125 pr_info("in xstateregs_set");
> 126
> 127 /*
> 128 * A whole standard-format XSAVE buffer is needed:
> 129 */
> 130 if ((pos != 0) || (count < fpu_user_xstate_size)) {
> 131 pr_info("EFAULT from xstateregs_set");
> 132-> pr_info("pos = %i, count = %i, fpu_user_xstate_size= %i\n", pos, count, fpu_user_xstate_size);
> 133 return -EFAULT;
> 134 }
>
> Sadly I had to fallback to debugging by printk because kgdb/qemu
> gdbstub, all didn't work for some unknown reason :-(
As always. printk is best debugger ever. ;-)
> output is:
> [ 69.598349] EFAULT from xstateregs_set
> [ 69.598350] pos = 0, count = 832, fpu_user_xstate_size= 1088
>
> calling code is in arch/x86/um/os-Linux/registers.c:
>
> 49 int restore_fp_registers(int pid, unsigned long *fp_regs)
> 50 {
> 51 struct iovec iov;
> 52
> 53 if (have_xstate_support) {
> 54 iov.iov_base = fp_regs;
> 55 iov.iov_len = sizeof(struct _xstate);
> 56 if (ptrace(PTRACE_SETREGSET, pid, NT_X86_XSTATE, &iov) < 0)
> 57 -> return -errno;
> 58 return 0;
> 59 } else {
> 60 return restore_i387_registers(pid, fp_regs);
> 61 }
> 62 }
>
> it looks like _xstate is too short for above operation, I wonder why
> PTRACE_GETREGSET works without a warning of too short size.
Does PTRACE_GETREGSET return a size? Maybe we have to take this into account.
It could be that your host CPU has a smaller set.
Also check whether PTRACE_SETREGSET always fails.
Thanks,
//richard
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From: Thomas M. <th...@m3...> - 2017-06-20 08:49:21
|
Am Dienstag, den 20.06.2017, 08:58 +0200 schrieb Richard Weinberger:
> Thomas,
>
> Am 20.06.2017 um 03:56 schrieb Thomas Meyer:
> > Hi,
> >
> > I finally did figure out where in the host kernel the ptrace
> > syscall
> > fails with -EFAULT.
>
> Nice! Thanks a lot for digging into this. I still had no chance to
> setup
> Ipv6 to connect to your host and figure myself. ;-\
>
> > In arch/x86/kernel/fpu/regset.c:130:
> >
> > 114 int xstateregs_set(struct task_struct *target, const struct
> > user_regset *regset,
> > 115 unsigned int pos, unsigned int count,
> > 116 const void *kbuf, const void __user *ubuf)
> > 117 {
> > 118 struct fpu *fpu = &target->thread.fpu;
> > 119 struct xregs_state *xsave;
> > 120 int ret;
> > 121
> > 122 if (!boot_cpu_has(X86_FEATURE_XSAVE))
> > 123 return -ENODEV;
> > 124
> > 125 pr_info("in xstateregs_set");
> > 126
> > 127 /*
> > 128 * A whole standard-format XSAVE buffer is needed:
> > 129 */
> > 130 if ((pos != 0) || (count < fpu_user_xstate_size)) {
> > 131 pr_info("EFAULT from xstateregs_set");
> > 132-> pr_info("pos = %i, count = %i,
> > fpu_user_xstate_size= %i\n", pos, count, fpu_user_xstate_size);
> > 133 return -EFAULT;
> > 134 }
> >
> > Sadly I had to fallback to debugging by printk because kgdb/qemu
> > gdbstub, all didn't work for some unknown reason :-(
>
> As always. printk is best debugger ever. ;-)
>
> > output is:
> > [ 69.598349] EFAULT from xstateregs_set
> > [ 69.598350] pos = 0, count = 832, fpu_user_xstate_size= 1088
> >
> > calling code is in arch/x86/um/os-Linux/registers.c:
> >
> > 49 int restore_fp_registers(int pid, unsigned long *fp_regs)
> > 50 {
> > 51 struct iovec iov;
> > 52
> > 53 if (have_xstate_support) {
> > 54 iov.iov_base = fp_regs;
> > 55 iov.iov_len = sizeof(struct _xstate);
> > 56 if (ptrace(PTRACE_SETREGSET, pid,
> > NT_X86_XSTATE, &iov) < 0)
> > 57 -> return -errno;
> > 58 return 0;
> > 59 } else {
> > 60 return restore_i387_registers(pid, fp_regs);
> > 61 }
> > 62 }
> >
> > it looks like _xstate is too short for above operation, I wonder
> > why
> > PTRACE_GETREGSET works without a warning of too short size.
>
> Does PTRACE_GETREGSET return a size?
Yes, it returns 832. the size of struct _xstate.
> Maybe we have to take this into account.
> It could be that your host CPU has a smaller set.
> Also check whether PTRACE_SETREGSET always fails.
In UML the first userspace ptrace always fails, so init get's killed.
The check "count < fpu_user_xstate_size" was introduced by commit:
commit 91c3dba7dbc199191272f4a9863f86ea3bfd679f
Author: Yu-cheng Yu <yu-...@in...>
Date: Fri Jun 17 13:07:17 2016 -0700
x86/fpu/xstate: Fix PTRACE frames for XSAVES
XSAVES uses compacted format and is a kernel instruction. The kernel
should use standard-format, non-supervisor state data for PTRACE.
So to summarize:
- PTRACE_GETREGSET with NT_X86_XSTATE gets 832 and return 832, with no
error.
- PTRACE_SETREGSET get 832 (sizeof struct _xstate) but wants at least
1088, otherwise it will fail with -EFAULT (why not -EINVAL?)
Ideas?
>
> Thanks,
> //richard
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From: Richard W. <ri...@no...> - 2017-06-20 09:06:04
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[adding x86 folks]
Am 20.06.2017 um 10:49 schrieb Thomas Meyer:
> Am Dienstag, den 20.06.2017, 08:58 +0200 schrieb Richard Weinberger:
>> Thomas,
>>
>> Am 20.06.2017 um 03:56 schrieb Thomas Meyer:
>>> Hi,
>>>
>>> I finally did figure out where in the host kernel the ptrace
>>> syscall
>>> fails with -EFAULT.
>>
>> Nice! Thanks a lot for digging into this. I still had no chance to
>> setup
>> Ipv6 to connect to your host and figure myself. ;-\
>>
>>> In arch/x86/kernel/fpu/regset.c:130:
>>>
>>> 114 int xstateregs_set(struct task_struct *target, const struct
>>> user_regset *regset,
>>> 115 unsigned int pos, unsigned int count,
>>> 116 const void *kbuf, const void __user *ubuf)
>>> 117 {
>>> 118 struct fpu *fpu = &target->thread.fpu;
>>> 119 struct xregs_state *xsave;
>>> 120 int ret;
>>> 121
>>> 122 if (!boot_cpu_has(X86_FEATURE_XSAVE))
>>> 123 return -ENODEV;
>>> 124
>>> 125 pr_info("in xstateregs_set");
>>> 126
>>> 127 /*
>>> 128 * A whole standard-format XSAVE buffer is needed:
>>> 129 */
>>> 130 if ((pos != 0) || (count < fpu_user_xstate_size)) {
>>> 131 pr_info("EFAULT from xstateregs_set");
>>> 132-> pr_info("pos = %i, count = %i,
>>> fpu_user_xstate_size= %i\n", pos, count, fpu_user_xstate_size);
>>> 133 return -EFAULT;
>>> 134 }
>>>
>>> Sadly I had to fallback to debugging by printk because kgdb/qemu
>>> gdbstub, all didn't work for some unknown reason :-(
>>
>> As always. printk is best debugger ever. ;-)
>>
>>> output is:
>>> [ 69.598349] EFAULT from xstateregs_set
>>> [ 69.598350] pos = 0, count = 832, fpu_user_xstate_size= 1088
>>>
>>> calling code is in arch/x86/um/os-Linux/registers.c:
>>>
>>> 49 int restore_fp_registers(int pid, unsigned long *fp_regs)
>>> 50 {
>>> 51 struct iovec iov;
>>> 52
>>> 53 if (have_xstate_support) {
>>> 54 iov.iov_base = fp_regs;
>>> 55 iov.iov_len = sizeof(struct _xstate);
>>> 56 if (ptrace(PTRACE_SETREGSET, pid,
>>> NT_X86_XSTATE, &iov) < 0)
>>> 57 -> return -errno;
>>> 58 return 0;
>>> 59 } else {
>>> 60 return restore_i387_registers(pid, fp_regs);
>>> 61 }
>>> 62 }
>>>
>>> it looks like _xstate is too short for above operation, I wonder
>>> why
>>> PTRACE_GETREGSET works without a warning of too short size.
>>
>> Does PTRACE_GETREGSET return a size?
>
> Yes, it returns 832. the size of struct _xstate.
>
>> Maybe we have to take this into account.
>> It could be that your host CPU has a smaller set.
>> Also check whether PTRACE_SETREGSET always fails.
>
> In UML the first userspace ptrace always fails, so init get's killed.
>
> The check "count < fpu_user_xstate_size" was introduced by commit:
>
> commit 91c3dba7dbc199191272f4a9863f86ea3bfd679f
> Author: Yu-cheng Yu <yu-...@in...>
> Date: Fri Jun 17 13:07:17 2016 -0700
>
> x86/fpu/xstate: Fix PTRACE frames for XSAVES
>
> XSAVES uses compacted format and is a kernel instruction. The kernel
> should use standard-format, non-supervisor state data for PTRACE.
>
> So to summarize:
>
> - PTRACE_GETREGSET with NT_X86_XSTATE gets 832 and return 832, with no
> error.
>
> - PTRACE_SETREGSET get 832 (sizeof struct _xstate) but wants at least
> 1088, otherwise it will fail with -EFAULT (why not -EINVAL?)
>
> Ideas?
>
>>
>> Thanks,
>> //richard
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From: Richard W. <ri...@no...> - 2017-06-20 18:17:48
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Yu-cheng, Am 20.06.2017 um 20:04 schrieb Yu-cheng Yu: >>> So to summarize: >>> >>> - PTRACE_GETREGSET with NT_X86_XSTATE gets 832 and return 832, with no >>> error. >>> >>> - PTRACE_SETREGSET get 832 (sizeof struct _xstate) but wants at least >>> 1088, otherwise it will fail with -EFAULT (why not -EINVAL?) >>> >>> Ideas? > > We considered allowing a partial XSAVE buffer for PTRACE_SETREGSET, but > it was that the XSAVE instruction requires a full-size buffer led to > this choice. Using a smaller buffer for XSAVE causes a fault. So, this code is not supposed to work? iov.iov_base = fp_regs; iov.iov_len = sizeof(struct _xstate); ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov); ptrace(PTRACE_SETREGSET, pid, NT_X86_XSTATE, &iov); This is what UML does and on Thomas's new Laptop PTRACE_SETREGSET is failing. Thanks, //richard |
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From: Richard W. <ri...@no...> - 2017-06-20 18:59:37
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Yu-cheng, Am 20.06.2017 um 20:17 schrieb Richard Weinberger: > Yu-cheng, > > Am 20.06.2017 um 20:04 schrieb Yu-cheng Yu: >>>> So to summarize: >>>> >>>> - PTRACE_GETREGSET with NT_X86_XSTATE gets 832 and return 832, with no >>>> error. >>>> >>>> - PTRACE_SETREGSET get 832 (sizeof struct _xstate) but wants at least >>>> 1088, otherwise it will fail with -EFAULT (why not -EINVAL?) >>>> >>>> Ideas? >> >> We considered allowing a partial XSAVE buffer for PTRACE_SETREGSET, but >> it was that the XSAVE instruction requires a full-size buffer led to >> this choice. Using a smaller buffer for XSAVE causes a fault. > > So, this code is not supposed to work? > > iov.iov_base = fp_regs; > iov.iov_len = sizeof(struct _xstate); > ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov); > ptrace(PTRACE_SETREGSET, pid, NT_X86_XSTATE, &iov); > > This is what UML does and on Thomas's new Laptop PTRACE_SETREGSET is failing. Hmm, I think we need to do what gdb does, it uses a buffer of size X86_XSTATE_MAX_SIZE. Thanks, //richard |
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From: Thomas M. <th...@m3...> - 2017-06-20 20:13:45
Attachments:
smime.p7s
|
> Am 20.06.2017 um 21:53 schrieb Yu-cheng Yu <yu-...@in...>: > >> On Tue, 2017-06-20 at 20:59 +0200, Richard Weinberger wrote: >> Yu-cheng, >> >>> Am 20.06.2017 um 20:17 schrieb Richard Weinberger: >>> Yu-cheng, >>> >>> Am 20.06.2017 um 20:04 schrieb Yu-cheng Yu: >>>>>> So to summarize: >>>>>> >>>>>> - PTRACE_GETREGSET with NT_X86_XSTATE gets 832 and return 832, with no >>>>>> error. >>>>>> >>>>>> - PTRACE_SETREGSET get 832 (sizeof struct _xstate) but wants at least >>>>>> 1088, otherwise it will fail with -EFAULT (why not -EINVAL?) >>>>>> >>>>>> Ideas? >>>> >>>> We considered allowing a partial XSAVE buffer for PTRACE_SETREGSET, but >>>> it was that the XSAVE instruction requires a full-size buffer led to >>>> this choice. Using a smaller buffer for XSAVE causes a fault. >>> >>> So, this code is not supposed to work? >>> >>> iov.iov_base = fp_regs; >>> iov.iov_len = sizeof(struct _xstate); >>> ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov); >>> ptrace(PTRACE_SETREGSET, pid, NT_X86_XSTATE, &iov); >>> >>> This is what UML does and on Thomas's new Laptop PTRACE_SETREGSET is failing. >> >> Hmm, I think we need to do what gdb does, it uses a buffer of size X86_XSTATE_MAX_SIZE. > > Linux kernel determines XSAVE buffer size from CPUID: > http://elixir.free-electrons.com/linux/latest/source/arch/x86/kernel/fpu/xstate.c#L626 Hi, Is there a user space API to get this value? > > GDB has a fixed X86_XSTATE_MAX_SIZE of 2688. That can become an issue. > > Yu-cheng > > |
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From: Natale P. <nat...@gm...> - 2017-06-21 08:39:19
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2017-06-20 22:13 GMT+02:00 Thomas Meyer <th...@m3...>: > >> Am 20.06.2017 um 21:53 schrieb Yu-cheng Yu <yu-...@in...>: >> >>> On Tue, 2017-06-20 at 20:59 +0200, Richard Weinberger wrote: >>> Yu-cheng, >>> >>>> Am 20.06.2017 um 20:17 schrieb Richard Weinberger: >>>> Yu-cheng, >>>> >>>> Am 20.06.2017 um 20:04 schrieb Yu-cheng Yu: >>>>>>> So to summarize: >>>>>>> >>>>>>> - PTRACE_GETREGSET with NT_X86_XSTATE gets 832 and return 832, with no >>>>>>> error. >>>>>>> >>>>>>> - PTRACE_SETREGSET get 832 (sizeof struct _xstate) but wants at least >>>>>>> 1088, otherwise it will fail with -EFAULT (why not -EINVAL?) >>>>>>> >>>>>>> Ideas? [cut text and CC'ed persons] It is funny to see that this problem was firstly reported here [1] in February 2017 without being considered until someone else bought a new laptop :) Anyway, thank you for digging into this; my temporary workaround at the time was to use always the *_i387_registers functions. HTH, Nat [1] https://sourceforge.net/p/user-mode-linux/mailman/message/35663374/ |
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From: Thomas M. <th...@m3...> - 2017-06-21 09:44:38
|
Am Mittwoch, den 21.06.2017, 10:39 +0200 schrieb Natale Patriciello:
> 2017-06-20 22:13 GMT+02:00 Thomas Meyer <th...@m3...>:
> >
> > > Am 20.06.2017 um 21:53 schrieb Yu-cheng Yu <yu-...@in...
> > > >:
> > >
> > > > On Tue, 2017-06-20 at 20:59 +0200, Richard Weinberger wrote:
> > > > Yu-cheng,
> > > >
> > > > > Am 20.06.2017 um 20:17 schrieb Richard Weinberger:
> > > > > Yu-cheng,
> > > > >
> > > > > Am 20.06.2017 um 20:04 schrieb Yu-cheng Yu:
> > > > > > > > So to summarize:
> > > > > > > >
> > > > > > > > - PTRACE_GETREGSET with NT_X86_XSTATE gets 832 and
> > > > > > > > return 832, with no
> > > > > > > > error.
> > > > > > > >
> > > > > > > > - PTRACE_SETREGSET get 832 (sizeof struct _xstate) but
> > > > > > > > wants at least
> > > > > > > > 1088, otherwise it will fail with -EFAULT (why not
> > > > > > > > -EINVAL?)
> > > > > > > >
> > > > > > > > Ideas?
>
> [cut text and CC'ed persons]
>
> It is funny to see that this problem was firstly reported here [1] in
> February 2017 without being considered until someone else bought a
> new
> laptop :)
>
Yes, I like my new laptop :-)
> Anyway, thank you for digging into this; my temporary workaround at
> the time was to use always the *_i387_registers functions.
Oops, there is the complete thread with the same problem. But sorry I
don't follow uml-user, just uml-devel :-(
As a quick fix you can try this:
diff --git a/arch/x86/um/os-Linux/registers.c b/arch/x86/um/os-Linux/registers.c
index 00f54a91bb4b..6eac8220ab29 100644
--- a/arch/x86/um/os-Linux/registers.c
+++ b/arch/x86/um/os-Linux/registers.c
@@ -30,7 +30,7 @@ int save_fp_registers(int pid, unsigned long *fp_regs)
if (have_xstate_support) {
iov.iov_base = fp_regs;
- iov.iov_len = sizeof(struct _xstate);
+ iov.iov_len = HOST_FP_SIZE * sizeof(unsigned long);
if (ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov) < 0)
return -errno;
return 0;
@@ -49,10 +49,9 @@ int restore_i387_registers(int pid, unsigned long *fp_regs)
int restore_fp_registers(int pid, unsigned long *fp_regs)
{
struct iovec iov;
-
if (have_xstate_support) {
iov.iov_base = fp_regs;
- iov.iov_len = sizeof(struct _xstate);
+ iov.iov_len = HOST_FP_SIZE * sizeof(unsigned long);
if (ptrace(PTRACE_SETREGSET, pid, NT_X86_XSTATE, &iov) < 0)
return -errno;
return 0;
@@ -126,7 +125,7 @@ void arch_init_registers(int pid)
struct iovec iov;
iov.iov_base = &fp_regs;
- iov.iov_len = sizeof(struct _xstate);
+ iov.iov_len = HOST_FP_SIZE * sizeof(unsigned long);
if (ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov) == 0)
have_xstate_support = 1;
}
diff --git a/arch/x86/um/user-offsets.c b/arch/x86/um/user-offsets.c
index cb3c22370cf5..9dccbbbf2fd1 100644
--- a/arch/x86/um/user-offsets.c
+++ b/arch/x86/um/user-offsets.c
@@ -50,7 +50,7 @@ void foo(void)
DEFINE(HOST_GS, GS);
DEFINE(HOST_ORIG_AX, ORIG_EAX);
#else
- DEFINE(HOST_FP_SIZE, sizeof(struct _xstate) / sizeof(unsigned long));
+ DEFINE_LONGS(HOST_FP_SIZE, 2688);
DEFINE_LONGS(HOST_BX, RBX);
DEFINE_LONGS(HOST_CX, RCX);
DEFINE_LONGS(HOST_DI, RDI);
a better fix would be to make the fp regs in struct uml_pt_regs dynamic
depending on the current kernel idea of the xsave area size.
>
> HTH,
> Nat
>
> [1] https://sourceforge.net/p/user-mode-linux/mailman/message/3566337
> 4/
|
|
From: Richard W. <ri...@no...> - 2017-06-21 12:47:31
|
Thomas, Natale,
Am 21.06.2017 um 11:44 schrieb Thomas Meyer:
>> It is funny to see that this problem was firstly reported here [1] in
>> February 2017 without being considered until someone else bought a
>> new
>> laptop :)
sometimes mails/issues get lost...
> Yes, I like my new laptop :-)
>
>> Anyway, thank you for digging into this; my temporary workaround at
>> the time was to use always the *_i387_registers functions.
>
> Oops, there is the complete thread with the same problem. But sorry I
> don't follow uml-user, just uml-devel :-(
We really should merge these lists. ;-\
> As a quick fix you can try this:
>
> diff --git a/arch/x86/um/os-Linux/registers.c b/arch/x86/um/os-Linux/registers.c
> index 00f54a91bb4b..6eac8220ab29 100644
> --- a/arch/x86/um/os-Linux/registers.c
> +++ b/arch/x86/um/os-Linux/registers.c
> @@ -30,7 +30,7 @@ int save_fp_registers(int pid, unsigned long *fp_regs)
>
> if (have_xstate_support) {
> iov.iov_base = fp_regs;
> - iov.iov_len = sizeof(struct _xstate);
> + iov.iov_len = HOST_FP_SIZE * sizeof(unsigned long);
> if (ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov) < 0)
> return -errno;
> return 0;
> @@ -49,10 +49,9 @@ int restore_i387_registers(int pid, unsigned long *fp_regs)
> int restore_fp_registers(int pid, unsigned long *fp_regs)
> {
> struct iovec iov;
> -
> if (have_xstate_support) {
> iov.iov_base = fp_regs;
> - iov.iov_len = sizeof(struct _xstate);
> + iov.iov_len = HOST_FP_SIZE * sizeof(unsigned long);
> if (ptrace(PTRACE_SETREGSET, pid, NT_X86_XSTATE, &iov) < 0)
> return -errno;
> return 0;
> @@ -126,7 +125,7 @@ void arch_init_registers(int pid)
> struct iovec iov;
>
> iov.iov_base = &fp_regs;
> - iov.iov_len = sizeof(struct _xstate);
> + iov.iov_len = HOST_FP_SIZE * sizeof(unsigned long);
> if (ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov) == 0)
> have_xstate_support = 1;
> }
> diff --git a/arch/x86/um/user-offsets.c b/arch/x86/um/user-offsets.c
> index cb3c22370cf5..9dccbbbf2fd1 100644
> --- a/arch/x86/um/user-offsets.c
> +++ b/arch/x86/um/user-offsets.c
> @@ -50,7 +50,7 @@ void foo(void)
> DEFINE(HOST_GS, GS);
> DEFINE(HOST_ORIG_AX, ORIG_EAX);
> #else
> - DEFINE(HOST_FP_SIZE, sizeof(struct _xstate) / sizeof(unsigned long));
> + DEFINE_LONGS(HOST_FP_SIZE, 2688);
> DEFINE_LONGS(HOST_BX, RBX);
> DEFINE_LONGS(HOST_CX, RCX);
> DEFINE_LONGS(HOST_DI, RDI);
>
>
> a better fix would be to make the fp regs in struct uml_pt_regs dynamic
> depending on the current kernel idea of the xsave area size.
And we should consider a mechanism to save/restore the full regset only when needed.
Otherwise the context switch is even more slower.
Thanks,
//richard
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