[PATCH] prctl.2: Add note regarding the size of the output user space buffer for PR_GET_TID_ADDRESS operation on x32/n32

[PATCH] prctl.2: Add note regarding the size of the output user space buffer for PR_GET_TID_ADDRESS operation on x32/n32

[Eugene Syromyatnikov]

---
 man2/prctl.2 | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/man2/prctl.2 b/man2/prctl.2
index 5f84bb7..39b3e9a 100644
--- a/man2/prctl.2
+++ b/man2/prctl.2
@@ -988,7 +988,10 @@ flag, in the location pointed to by
 .IR "(int\ **)\ arg2" .
 This feature is available only if the kernel is built with the
 .BR CONFIG_CHECKPOINT_RESTORE
-option enabled.
+option enabled. Note that since the prctl() syscall does not have compat
+implementation for AMD64 x32 and MIPS n32 ABIs, and the kernel writes out
+pointer of kernel's pointer size, this operation expects a user space buffer
+of 8 (not 4) bytes on these ABIs.
 .TP
 .BR PR_SET_TIMERSLACK " (since Linux 2.6.28)"
 .\" See https://lwn.net/Articles/369549/
-- 
2.10.2

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Re: [PATCH] prctl.2: Add note regarding the size of the output user space buffer for PR_GET_TID_ADDRESS operation on x32/n32

[Michael Kerrisk (man-pages)]

On 12/12/2016 04:54 AM, Eugene Syromyatnikov wrote:

Thanks, Eugene. Applied.

Cheers,

Michael

> ---
>  man2/prctl.2 | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/man2/prctl.2 b/man2/prctl.2
> index 5f84bb7..39b3e9a 100644
> --- a/man2/prctl.2
> +++ b/man2/prctl.2
> @@ -988,7 +988,10 @@ flag, in the location pointed to by
>  .IR "(int\ **)\ arg2" .
>  This feature is available only if the kernel is built with the
>  .BR CONFIG_CHECKPOINT_RESTORE
> -option enabled.
> +option enabled. Note that since the prctl() syscall does not have compat
> +implementation for AMD64 x32 and MIPS n32 ABIs, and the kernel writes out
> +pointer of kernel's pointer size, this operation expects a user space buffer
> +of 8 (not 4) bytes on these ABIs.
>  .TP
>  .BR PR_SET_TIMERSLACK " (since Linux 2.6.28)"
>  .\" See https://lwn.net/Articles/369549/
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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Re: [PATCH] prctl.2: Add note regarding the size of the output user space buffer for PR_GET_TID_ADDRESS operation on x32/n32

[Michael Kerrisk (man-pages)]

On 12/12/2016 04:54 AM, Eugene Syromyatnikov wrote:
> ---
>  man2/prctl.2 | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)

Thanks, Eugene. Applied. (And fantastic to get patches with this
level of detail!)

Cheers,

Michael

> diff --git a/man2/prctl.2 b/man2/prctl.2
> index 5f84bb7..39b3e9a 100644
> --- a/man2/prctl.2
> +++ b/man2/prctl.2
> @@ -988,7 +988,10 @@ flag, in the location pointed to by
>  .IR "(int\ **)\ arg2" .
>  This feature is available only if the kernel is built with the
>  .BR CONFIG_CHECKPOINT_RESTORE
> -option enabled.
> +option enabled. Note that since the prctl() syscall does not have compat
> +implementation for AMD64 x32 and MIPS n32 ABIs, and the kernel writes out
> +pointer of kernel's pointer size, this operation expects a user space buffer
> +of 8 (not 4) bytes on these ABIs.
>  .TP
>  .BR PR_SET_TIMERSLACK " (since Linux 2.6.28)"
>  .\" See https://lwn.net/Articles/369549/
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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