linux-kernel - Re: [PATCH v3 5/6] s390/crash: Use note name macros

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Message-ID: <965b73e7-d0a3-4fae-b0ec-70b5497cb6c4@daynix.com>
Date: Wed, 8 Jan 2025 13:53:51 +0900
From: Akihiko Odaki <akihiko.odaki@...nix.com>
To: Dave Martin <Dave.Martin@....com>, Heiko Carstens <hca@...ux.ibm.com>,
 Vasily Gorbik <gor@...ux.ibm.com>, Alexander Gordeev
 <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>
Cc: Eric Biederman <ebiederm@...ssion.com>, Kees Cook <kees@...nel.org>,
 Catalin Marinas <catalin.marinas@....com>, Mark Brown <broonie@...nel.org>,
 Baoquan He <bhe@...hat.com>, Vivek Goyal <vgoyal@...hat.com>,
 Dave Young <dyoung@...hat.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 linux-s390@...r.kernel.org, kexec@...ts.infradead.org,
 binutils@...rceware.org, devel@...nix.com
Subject: Re: [PATCH v3 5/6] s390/crash: Use note name macros

On 2025/01/08 1:17, Dave Martin wrote:
> Hi,
> 
> On Tue, Jan 07, 2025 at 09:45:56PM +0900, Akihiko Odaki wrote:
>> Use note name macros to match with the userspace's expectation.
>>
>> Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
>> ---
>>   arch/s390/kernel/crash_dump.c | 62 ++++++++++++++++---------------------------
>>   1 file changed, 23 insertions(+), 39 deletions(-)
>>
>> diff --git a/arch/s390/kernel/crash_dump.c b/arch/s390/kernel/crash_dump.c
> 
> [...]
> 
>> @@ -281,10 +272,8 @@ static void *nt_init_name(void *buf, Elf64_Word type, void *desc, int d_len,
>>   	return PTR_ADD(buf, len);
>>   }
>>   
>> -static inline void *nt_init(void *buf, Elf64_Word type, void *desc, int d_len)
>> -{
>> -	return nt_init_name(buf, type, desc, d_len, nt_name(type));
>> -}
>> +#define NT_INIT(buf, type, desc) \
>> +	(nt_init_name((buf), NT_ ## type, &(desc), sizeof(desc), NN_ ## type))
> 
> Nit: this macro name clashes with the naming scheme in elf.h.
> 
> I think that there is a (weak) convention that macros with upper-case
> names don't expand to a C function call; thus, a macro with an upper-
> case name can be invoked in places where a C function call would not be
> allowed.  (This convention is not followed everywhere, though -- it's
> up to the maintainer what they prefer here.)

I wanted to clarify it is a macro as it concatenates tokens with ##, but 
I also find there are many macros that are named lower-case and performs 
token concatenation.

S390 maintainers, please tell usr your opinion.

> 
> (Note also, the outer parentheses and the parentheses around (buf)
> appear redundant -- although harmless?)

They only make a difference in trivial corner cases and may look 
needlessly verbose.

> 
>>   
>>   /*
>>    * Calculate the size of ELF note
>> @@ -300,10 +289,7 @@ static size_t nt_size_name(int d_len, const char *name)
>>   	return size;
>>   }
>>   
>> -static inline size_t nt_size(Elf64_Word type, int d_len)
>> -{
>> -	return nt_size_name(d_len, nt_name(type));
>> -}
>> +#define NT_SIZE(type, desc) (nt_size_name(sizeof(desc), NN_ ## type))
> 
> Nit: name prefix clash (again); possibly redundant parentheses.
> 
> [...]
> 
>> @@ -348,16 +332,16 @@ static size_t get_cpu_elf_notes_size(void)
>>   	struct save_area *sa = NULL;
>>   	size_t size;
>>   
>> -	size =	nt_size(NT_PRSTATUS, sizeof(struct elf_prstatus));
>> -	size +=  nt_size(NT_PRFPREG, sizeof(elf_fpregset_t));
>> -	size +=  nt_size(NT_S390_TIMER, sizeof(sa->timer));
>> -	size +=  nt_size(NT_S390_TODCMP, sizeof(sa->todcmp));
>> -	size +=  nt_size(NT_S390_TODPREG, sizeof(sa->todpreg));
>> -	size +=  nt_size(NT_S390_CTRS, sizeof(sa->ctrs));
>> -	size +=  nt_size(NT_S390_PREFIX, sizeof(sa->prefix));
>> +	size =	NT_SIZE(PRSTATUS, struct elf_prstatus);
>> +	size +=  NT_SIZE(PRFPREG, elf_fpregset_t);
>> +	size +=  NT_SIZE(S390_TIMER, sa->timer);
>> +	size +=  NT_SIZE(S390_TODCMP, sa->todcmp);
>> +	size +=  NT_SIZE(S390_TODPREG, sa->todpreg);
>> +	size +=  NT_SIZE(S390_CTRS, sa->ctrs);
>> +	size +=  NT_SIZE(S390_PREFIX, sa->prefix);
> 
> It might be worth fixing the funny spacing on these lines, since all
> the affected lines are being replaced.
> 
>>   	if (cpu_has_vx()) {
>> -		size += nt_size(NT_S390_VXRS_HIGH, sizeof(sa->vxrs_high));
>> -		size += nt_size(NT_S390_VXRS_LOW, sizeof(sa->vxrs_low));
>> +		size += NT_SIZE(S390_VXRS_HIGH, sa->vxrs_high);
>> +		size += NT_SIZE(S390_VXRS_LOW, sa->vxrs_low);
>>   	}
>>   
>>   	return size;
>> @@ -373,7 +357,7 @@ static void *nt_prpsinfo(void *ptr)
>>   	memset(&prpsinfo, 0, sizeof(prpsinfo));
>>   	prpsinfo.pr_sname = 'R';
>>   	strcpy(prpsinfo.pr_fname, "vmlinux");
>> -	return nt_init(ptr, NT_PRPSINFO, &prpsinfo, sizeof(prpsinfo));
>> +	return NT_INIT(ptr, PRPSINFO, prpsinfo);
>>   }
>>   
>>   /*
>> @@ -589,7 +573,7 @@ static size_t get_elfcorehdr_size(int phdr_count)
>>   	/* PT_NOTES */
>>   	size += sizeof(Elf64_Phdr);
>>   	/* nt_prpsinfo */
>> -	size += nt_size(NT_PRPSINFO, sizeof(struct elf_prpsinfo));
>> +	size += NT_SIZE(PRPSINFO, struct elf_prpsinfo);
>>   	/* regsets */
>>   	size += get_cpu_cnt() * get_cpu_elf_notes_size();
>>   	/* nt_vmcoreinfo */
> 
> Otherwise, this looks sensible to me.
> 
> Cheers
> ---Dave