Re: [PATCH] um: Allow building and running on older hosts

[Thomas Meyer]

> Am 24.05.2017 um 09:01 schrieb Richard Weinberger <richard@xxxxxx>:
> 
> CC'ing Thomas. We is also facing issues with these commits.
> 
>> Am 24.05.2017 um 03:08 schrieb Florian Fainelli:
>> 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.
>> 
>> 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@xxxxxxxxx>
>> ---
>> arch/x86/um/os-Linux/registers.c | 13 +++++++++----
>> arch/x86/um/user-offsets.c       |  4 ++++
>> 2 files changed, 13 insertions(+), 4 deletions(-)
>> 
>> diff --git a/arch/x86/um/os-Linux/registers.c b/arch/x86/um/os-Linux/registers.c
>> index 00f54a91bb4b..502bd642e5c2 100644
>> --- a/arch/x86/um/os-Linux/registers.c
>> +++ b/arch/x86/um/os-Linux/registers.c
>> @@ -26,13 +26,14 @@ int save_i387_registers(int pid, unsigned long *fp_regs)
>> 
>> int save_fp_registers(int pid, unsigned long *fp_regs)
>> {
>> -    struct iovec iov;
>> -
>>    if (have_xstate_support) {
>> +#ifdef PTRACE_GETREGSET
>> +        struct iovec iov;

Is this okay, in C90? Won't this give an error once the thing is defined?

>>        iov.iov_base = fp_regs;
>>        iov.iov_len = sizeof(struct _xstate);
>>        if (ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov) < 0)
>>            return -errno;
>> +#endif
>>        return 0;
>>    } else {
>>        return save_i387_registers(pid, fp_regs);
>> @@ -48,13 +49,15 @@ int restore_i387_registers(int pid, unsigned long *fp_regs)
>> 
>> int restore_fp_registers(int pid, unsigned long *fp_regs)
>> {
>> -    struct iovec iov;
>> -
>>    if (have_xstate_support) {
>> +#ifdef PTRACE_SETREGSET
>> +        struct iovec iov;
>> +
>>        iov.iov_base = fp_regs;
>>        iov.iov_len = sizeof(struct _xstate);
>>        if (ptrace(PTRACE_SETREGSET, pid, NT_X86_XSTATE, &iov) < 0)
>>            return -errno;
>> +#endif
>>        return 0;
>>    } else {
>>        return restore_i387_registers(pid, fp_regs);
>> @@ -127,8 +130,10 @@ void arch_init_registers(int pid)
>> 
>>    iov.iov_base = &fp_regs;
>>    iov.iov_len = sizeof(struct _xstate);
>> +#ifdef PTRACE_GETREGSET
>>    if (ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov) == 0)
>>        have_xstate_support = 1;

So why keep have_xstate_support when all branches that test for it are now pre compiler conditionals?

>> +#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);
>>

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