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

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Message-ID: <465e4bf4-8d81-4d2f-8d50-92032e718fea@linux.ibm.com>
Date: Mon, 10 Feb 2025 16:56:39 +0100
From: Jens Remus <jremus@...ux.ibm.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: x86@...nel.org, Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-kernel@...r.kernel.org, Indu Bhagat <indu.bhagat@...cle.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org, Mark Brown <broonie@...nel.org>,
        linux-toolchains@...r.kernel.org, Jordan Rome <jordalgo@...a.com>,
        Sam James <sam@...too.org>, linux-trace-kernel@...r.kernel.org,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Florian Weimer <fweimer@...hat.com>, Andy Lutomirski <luto@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>, Weinan Liu <wnliu@...gle.com>,
        Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: [PATCH v4 19/39] unwind_user/sframe: Add support for reading
 .sframe contents

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@...ibm.com

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