linux-kernel - Re: [RFC PATCH 6/7] x86/kexec: Debugging support: Dump registers on exception

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Message-ID: <3a91abd7-5edd-4f4e-bb15-fb9c91f64cc9@zytor.com>
Date: Tue, 5 Nov 2024 14:57:28 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: "Woodhouse, David" <dwmw@...zon.co.uk>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "jpoimboe@...nel.org" <jpoimboe@...nel.org>
Cc: "horms@...nel.org" <horms@...nel.org>, "x86@...nel.org" <x86@...nel.org>,
        "bp@...en8.de" <bp@...en8.de>, "mingo@...hat.com" <mingo@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "kai.huang@...el.com" <kai.huang@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "nik.borisov@...e.com" <nik.borisov@...e.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
Subject: Re: [RFC PATCH 6/7] x86/kexec: Debugging support: Dump registers on
 exception

On 11/5/24 14:27, H. Peter Anvin wrote:
> 
> I don't know if it is necessary, but you can do something like this to 
> make absolutely sure you don't end up with non-relative symbol references:
> 
> static inline __constfunc void * sym_addr(const void *sym)
> {
>      void *addr;
>      asm("lea %c1(%%rip),%0" : "=r" (addr) : "i" (sym));
>      return addr;
> }
> 

Compiling with "-fpic -fvisibility=hidden -mcmodel=medium" can also be 
used to suppress non-relative references. If you have external symbol 
references they at least *should* be emitted as GOTPCRELX relocations 
which the linker should relax to relative references; however, I would 
think that you really don't want any of those :)

	-hpa