Re: [tip: x86/fred] x86/ptrace: Cleanup the definition of the pt_regs structure

Xin Li
2024-02-06T19:04:37Z

On 2/3/2024 3:52 PM, H. Peter Anvin wrote:
> On January 31, 2024 1:14:52 PM PST, tip-bot2 for Xin Li <tip-bot2@linutronix.de> wrote:
>> The following commit has been merged into the x86/fred branch of tip:
>>
>> Commit-ID: ee63291aa8287cb7ded767d340155fe8681fc075
>> Gitweb: https://git.kernel.org/tip/ee63291aa8287cb7ded767d340155fe8681fc075
>> Author: Xin Li <xin3.li@intel.com>
>> AuthorDate: Tue, 05 Dec 2023 02:50:02 -08:00
>> Committer: Borislav Petkov (AMD) <bp@alien8.de>
>> CommitterDate: Wed, 31 Jan 2024 22:01:13 +01:00
>>
>> x86/ptrace: Cleanup the definition of the pt_regs structure
>>
>> struct pt_regs is hard to read because the member or section related
>> comments are not aligned with the members.
>>
>> The 'cs' and 'ss' members of pt_regs are type of 'unsigned long' while
>> in reality they are only 16-bit wide. This works so far as the
>> remaining space is unused, but FRED will use the remaining bits for
>> other purposes.
>>
>> To prepare for FRED:
>>
>> - Cleanup the formatting
>> - Convert 'cs' and 'ss' to u16 and embed them into an union
>> with a u64
>> - Fixup the related printk() format strings
>>
>> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
>> Originally-by: H. Peter Anvin (Intel) <hpa@zytor.com>
>> Signed-off-by: Xin Li <xin3.li@intel.com>
>> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
>> Tested-by: Shan Kang <shan.kang@intel.com>
>> Link: https://lore.kernel.org/r/20231205105030.8698-14-xin3.li@intel.com

[...]

>> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
>> index 33b2687..0f78b58 100644
>> --- a/arch/x86/kernel/process_64.c
>> +++ b/arch/x86/kernel/process_64.c
>> @@ -117,7 +117,7 @@ void __show_regs(struct pt_regs *regs, enum show_regs_mode mode,
>>
>> printk("%sFS: %016lx(%04x) GS:%016lx(%04x) knlGS:%016lx\n",
>> log_lvl, fs, fsindex, gs, gsindex, shadowgs);
>> - printk("%sCS: %04lx DS: %04x ES: %04x CR0: %016lx\n",
>> + printk("%sCS: %04x DS: %04x ES: %04x CR0: %016lx\n",
>> log_lvl, regs->cs, ds, es, cr0);
>> printk("%sCR2: %016lx CR3: %016lx CR4: %016lx\n",
>> log_lvl, cr2, cr3, cr4);
>
> Incidentally, the comment about callee-saved registers is long since both obsolete and is now outright wrong.
>
> The next version of gcc (14 I think) will have an attribute to turn off saving registers which we can use for top-level C functions.
>

Forgive my ignorance, do we have an official definition for "top-level C
functions"?

Thanks!
Xin