Re: [PATCH v4 19/39] unwind_user/sframe: Add support for reading .sframe contents

Jens Remus
2025-02-10T15:57:48Z

On 07.02.2025 22:06, Josh Poimboeuf wrote:
> On Wed, Feb 05, 2025 at 10:47:58AM +0100, Jens Remus wrote:
>> UNSAFE_GET_USER_INC(ra_off, cur, offset_size, Efault);
>>
>> With offset_size=1 expands into:
>>
>> __UNSAFE_GET_USER_INC(/*to=*/ra_off, /*from=*cur, /*type=*/u8, /*label=*/Efault);
>>
>> Expands into:
>>
>> {
>> u8 __to;
>> unsafe_get_user(__to, (u8 __user *)cur, Efault);
>> cur += sizeof(__to);
>> ra_off = (typeof(ra_off))__to;
>> }
>>
>> The issue is that on the last line __to is u8 instead of s8 and thus
>> u8 gets casted to s32, which is performed without sign extension. __to
>> would need to be s8 or get casted to s8 for sign extension to take
>> place.
>
> Ah, I get it now, thanks for spelling that out for me.
>
> Here's what I have at the moment:

Thanks! Using your new UNSAFE_GET_USER_INC() in all places works great
on s390 when resolving the duplicate macro names (see below).

>
> #define __UNSAFE_GET_USER_INC(to, from, type, label) \
> ({ \
> type __to; \
> unsafe_get_user(__to, (type __user *)from, label); \
> from += sizeof(__to); \
> to = __to; \
> })
>
> #define __UNSAFE_GET_USER_INC(to, from, size, label, u_or_s) \

That does not compile. One of the macros needs to be renamed.

CC kernel/unwind/sframe.o
kernel/unwind/sframe.c:141:9: warning: "__UNSAFE_GET_USER_INC" redefined
141 | #define __UNSAFE_GET_USER_INC(to, from, size, label, u_or_s) \
| ^~~~~~~~~~~~~~~~~~~~~
kernel/unwind/sframe.c:133:9: note: this is the location of the previous definition
133 | #define __UNSAFE_GET_USER_INC(to, from, type, label) \
| ^~~~~~~~~~~~~~~~~~~~~

> ({ \
> switch (size) { \
> case 1: \
> __UNSAFE_GET_USER_INC(to, from, u_or_s##8, label); \
> break; \
> case 2: \
> __UNSAFE_GET_USER_INC(to, from, u_or_s##16, label); \
> break; \
> case 4: \
> __UNSAFE_GET_USER_INC(to, from, u_or_s##32, label); \
> break; \
> default: \
> dbg_sec_uaccess("%d: bad unsafe_get_user() size %u\n", \
> __LINE__, size); \
> return -EFAULT; \
> } \
> })
>
> #define UNSAFE_GET_USER_UNSIGNED_INC(to, from, size, label) \
> __UNSAFE_GET_USER_INC(to, from, size, label, u)
>
> #define UNSAFE_GET_USER_SIGNED_INC(to, from, size, label) \
> __UNSAFE_GET_USER_INC(to, from, size, label, s)
>
> #define UNSAFE_GET_USER_INC(to, from, size, label) \
> _Generic(to, \
> u8: UNSAFE_GET_USER_UNSIGNED_INC(to, from, size, label), \
> u16: UNSAFE_GET_USER_UNSIGNED_INC(to, from, size, label), \
> u32: UNSAFE_GET_USER_UNSIGNED_INC(to, from, size, label), \
> s8: UNSAFE_GET_USER_SIGNED_INC(to, from, size, label), \
> s16: UNSAFE_GET_USER_SIGNED_INC(to, from, size, label), \
> s32: UNSAFE_GET_USER_SIGNED_INC(to, from, size, label))

Regards,
Jens
--
Jens Remus
Linux on Z Development (D3303)
+49-7031-16-1128 Office
jremus@de.ibm.com

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