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Message-Id: <B6DC63CC-D5A9-4A56-9832-DD6BD1720CBC@m3y3r.de>
Date: Thu, 25 May 2017 21:51:53 +0200
From: Thomas Meyer <thomas@...3r.de>
To: Florian Fainelli <f.fainelli@...il.com>
Cc: linux-kernel@...r.kernel.org, elicooper@....com,
Jeff Dike <jdike@...toit.com>,
Richard Weinberger <richard@....at>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
"open list:USER-MODE LINUX (UML)"
<user-mode-linux-devel@...ts.sourceforge.net>,
"open list:USER-MODE LINUX (UML)"
<user-mode-linux-user@...ts.sourceforge.net>
Subject: Re: [PATCH v2] um: Allow building and running on older hosts
> Am 25.05.2017 um 20:36 schrieb Florian Fainelli <f.fainelli@...il.com>:
>
> Commit a78ff1112263 ("um: add extended processor state save/restore
> support") and b6024b21fec8 ("um: extend fpstate to _xstate to support
> YMM registers") forced the use of the x86 FP _xstate and
> PTRACE_GETREGSET/SETREGSET. On older hosts, we would neither be able to
> build UML nor run it anymore with these two commits applied because we
> don't have definitions for struct _xstate nor these two ptrace requests.
Btw. what soy you mean with older host? I need to revert two commits to make an UML kernel work again on a Fedora 25 installation.
>
> We can determine at build time which fp context structure to check
> against, just like we can keep using the old i387 fp save/restore if
> PTRACE_GETRESET/SETREGSET are not defined.
>
> Fixes: a78ff1112263 ("um: add extended processor state save/restore support")
> Fixes: b6024b21fec8 ("um: extend fpstate to _xstate to support YMM registers")
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---
> Changes in v2:
>
> - re-arrange the #ifdef/curly braces to not take the branch
>
> arch/x86/um/os-Linux/registers.c | 12 ++++++++----
> arch/x86/um/user-offsets.c | 4 ++++
> 2 files changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/um/os-Linux/registers.c b/arch/x86/um/os-Linux/registers.c
> index 00f54a91bb4b..28775f55bde2 100644
> --- a/arch/x86/um/os-Linux/registers.c
> +++ b/arch/x86/um/os-Linux/registers.c
> @@ -26,6 +26,7 @@ int save_i387_registers(int pid, unsigned long *fp_regs)
>
> int save_fp_registers(int pid, unsigned long *fp_regs)
> {
> +#ifdef PTRACE_GETREGSET
> struct iovec iov;
>
> if (have_xstate_support) {
> @@ -34,9 +35,9 @@ int save_fp_registers(int pid, unsigned long *fp_regs)
> if (ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov) < 0)
> return -errno;
> return 0;
> - } else {
> + } else
> +#endif
> return save_i387_registers(pid, fp_regs);
> - }
> }
>
> int restore_i387_registers(int pid, unsigned long *fp_regs)
> @@ -48,6 +49,7 @@ int restore_i387_registers(int pid, unsigned long *fp_regs)
>
> int restore_fp_registers(int pid, unsigned long *fp_regs)
> {
> +#ifdef PTRACE_SETREGSET
> struct iovec iov;
>
> if (have_xstate_support) {
> @@ -56,9 +58,9 @@ int restore_fp_registers(int pid, unsigned long *fp_regs)
> if (ptrace(PTRACE_SETREGSET, pid, NT_X86_XSTATE, &iov) < 0)
> return -errno;
> return 0;
> - } else {
> + } else
> +#endif
> return restore_i387_registers(pid, fp_regs);
> - }
> }
>
> #ifdef __i386__
> @@ -122,6 +124,7 @@ int put_fp_registers(int pid, unsigned long *regs)
>
> void arch_init_registers(int pid)
> {
> +#ifdef PTRACE_GETREGSET
> struct _xstate fp_regs;
> struct iovec iov;
>
> @@ -129,6 +132,7 @@ void arch_init_registers(int pid)
> iov.iov_len = sizeof(struct _xstate);
> if (ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov) == 0)
> have_xstate_support = 1;
In my setup above call works correctly and so have_xstate_support will be set, but save_fp_registers fails with errno 4 or so...
> +#endif
> }
> #endif
>
> diff --git a/arch/x86/um/user-offsets.c b/arch/x86/um/user-offsets.c
> index cb3c22370cf5..8af0fb5d2780 100644
> --- a/arch/x86/um/user-offsets.c
> +++ b/arch/x86/um/user-offsets.c
> @@ -50,7 +50,11 @@ void foo(void)
> DEFINE(HOST_GS, GS);
> DEFINE(HOST_ORIG_AX, ORIG_EAX);
> #else
> +#if defined(PTRACE_GETREGSET) && defined(PTRACE_SETREGSET)
> DEFINE(HOST_FP_SIZE, sizeof(struct _xstate) / sizeof(unsigned long));
> +#else
> + DEFINE(HOST_FP_SIZE, sizeof(struct _fpstate) / sizeof(unsigned long));
> +#endif
> DEFINE_LONGS(HOST_BX, RBX);
> DEFINE_LONGS(HOST_CX, RCX);
> DEFINE_LONGS(HOST_DI, RDI);
> --
> 2.12.2
>
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