linux-kernel - Re: Fwd: struct pt_regs missing in /usr/include/ tree for eBPF program compile

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Date:   Mon, 14 Aug 2017 16:39:03 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Heiko Carstens <heiko.carstens@...ibm.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Thomas-Mich Richter <tmricht@...ux.vnet.ibm.com>,
        ast@...nel.org, Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
        David Miller <davem@...emloft.net>, yhs@...com,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: Fwd: struct pt_regs missing in /usr/include/ tree for eBPF
 program compile

On Mon, Aug 14, 2017 at 2:08 PM, Heiko Carstens
<heiko.carstens@...ibm.com> wrote:
>
> I really don't think that struct pt_regs is part of uapi and should be
> exported. We did change the layout of the pt_regs structure more than once
> and would like to be able to do so in the future as well.

On some architectures, pt_regs is definitely part of the uapi, as
we define sigcontext in terms of pt_regs:

arch/cris/include/uapi/asm/sigcontext.h:        struct pt_regs regs;
/* needs to be first */
arch/m32r/include/uapi/asm/sigcontext.h:        struct pt_regs *sc_pt_regs;
arch/microblaze/include/uapi/asm/sigcontext.h:  struct pt_regs regs;
arch/powerpc/include/uapi/asm/sigcontext.h:     struct pt_regs  __user *regs;
arch/tile/include/uapi/asm/sigcontext.h: * struct sigcontext has the
same shape as struct pt_regs,
arch/unicore32/include/uapi/asm/sigcontext.h:   struct pt_regs regs;

On other architectures, they just use the same layout but different names.

arm32 also uses pt_regs in struct kvm_regs, the other ones don't:

arch/arm/include/uapi/asm/kvm.h:        struct pt_regs usr_regs;
 /* R0_usr - R14_usr, PC, CPSR */

> In addition what about compat processes? Most architectures define their
> struct pt_regs with "unsigned long" members, which have different sizes for
> 32/64 bit, while the structure on the kernel stack contains 64 bit
> members. And as far as I know the bpf test cases want to access the kernel
> stack, no? Then this seems to be broken also.

Right.

      Arnd