From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <jbeulich@suse.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: "Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [PATCH 3/5] x86/ELF: don't store function pointer in elf_core_save_regs()
Date: Mon, 28 Sep 2020 13:58:40 +0100 [thread overview]
Message-ID: <33b47445-8de4-24f0-69b0-74119f10d7e9@citrix.com> (raw)
In-Reply-To: <8abe7016-1cd7-246e-24ef-92d92ff27ad3@suse.com>
On 28/09/2020 13:06, Jan Beulich wrote:
> This keeps at least gcc 10 from generating a separate function instance
> in common/kexec.o alongside the inlining of the function in its sole
> caller. I also think putting the address of the actual code storing the
> registers is a better indication to consumers than that of an otherwise
> unreferenced function.
Hmm - that's unfortunate.
elf_core_save_regs is certainly a useful name to spot in a backtrace.
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>
> --- a/xen/include/asm-x86/x86_64/elf.h
> +++ b/xen/include/asm-x86/x86_64/elf.h
> @@ -54,7 +54,7 @@ static inline void elf_core_save_regs(EL
> asm volatile("movq %%rsi,%0" : "=m"(core_regs->rsi));
> asm volatile("movq %%rdi,%0" : "=m"(core_regs->rdi));
> /* orig_rax not filled in for now */
> - core_regs->rip = (unsigned long)elf_core_save_regs;
> + asm volatile("call 0f; 0: popq %0" : "=m" (core_regs->rip));
lea 0(%rip) will be faster to execute, and this is 64bit code specifically.
Either way, Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
> core_regs->cs = read_sreg(cs);
> asm volatile("pushfq; popq %0" :"=m"(core_regs->rflags));
> asm volatile("movq %%rsp,%0" : "=m"(core_regs->rsp));
>
next prev parent reply other threads:[~2020-09-28 12:59 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-28 12:04 [PATCH 0/5] x86: introduce read_sregs() and elf_core_save_regs() adjustments Jan Beulich
2020-09-28 12:05 ` [PATCH 1/5] x86: introduce read_sregs() to allow storing to memory directly Jan Beulich
2020-09-28 12:47 ` Andrew Cooper
2020-09-28 13:29 ` Jan Beulich
2020-09-28 14:49 ` Jan Beulich
2020-09-28 15:11 ` Andrew Cooper
2020-09-28 12:05 ` [PATCH 2/5] x86/ELF: don't open-code read_sreg() Jan Beulich
2020-09-28 12:57 ` Andrew Cooper
2020-09-28 12:06 ` [PATCH 3/5] x86/ELF: don't store function pointer in elf_core_save_regs() Jan Beulich
2020-09-28 12:58 ` Andrew Cooper [this message]
2020-09-28 12:06 ` [PATCH 4/5] x86/ELF: also record FS/GS bases " Jan Beulich
2020-09-28 13:04 ` Andrew Cooper
2020-09-28 13:38 ` Jan Beulich
2020-09-28 12:07 ` [PATCH 5/5] x86/ELF: eliminate pointless local variable from elf_core_save_regs() Jan Beulich
2020-09-28 13:06 ` Andrew Cooper
2020-09-28 15:04 ` [PATCH 6/5] x86/ELF: drop unnecessary volatile from asm()-s in elf_core_save_regs() Jan Beulich
2020-09-28 15:15 ` Andrew Cooper
2020-09-28 15:40 ` Jan Beulich
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