From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH 6/8] xen/x86: Avoid overriding initialisers in arrays Date: Wed, 10 Feb 2016 13:50:58 +0000 Message-ID: <56BB4042.70409@citrix.com> References: <1455048108-5045-1-git-send-email-andrew.cooper3@citrix.com> <1455048108-5045-7-git-send-email-andrew.cooper3@citrix.com> <56BB47BF02000078000D08FC@prv-mh.provo.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <56BB47BF02000078000D08FC@prv-mh.provo.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich Cc: George Dunlap , Kevin Tian , JunNakajima , Xen-devel List-Id: xen-devel@lists.xenproject.org On 10/02/16 13:22, Jan Beulich wrote: >>>> On 09.02.16 at 21:01, wrote: >> Clang objects to having multiple initialisers when creating an array. >> >> As this warning is useful for spotting obscure bugs, disabling it is >> unhelpful. Instead, fix our two deliberate usecases. > Ugly again, but - well ... > >> --- a/xen/arch/x86/mm/p2m-ept.c >> +++ b/xen/arch/x86/mm/p2m-ept.c >> @@ -1201,6 +1201,20 @@ void ept_p2m_uninit(struct p2m_domain *p2m) >> free_cpumask_var(ept->invalidate); >> } >> >> +static const char *memory_type_to_str(unsigned int x) >> +{ >> + static const char memory_types[8][2] = { >> + [MTRR_TYPE_UNCACHABLE] = "UC", >> + [MTRR_TYPE_WRCOMB] = "WC", >> + [MTRR_TYPE_WRTHROUGH] = "WT", >> + [MTRR_TYPE_WRPROT] = "WP", >> + [MTRR_TYPE_WRBACK] = "WB", >> + [MTRR_NUM_TYPES] = "??" >> + }; >> + >> + return x < ARRAY_SIZE(memory_types) ? (memory_types[x] ?: "?") : "?"; > I think this should really ASSERT() the first condition. > >> @@ -1212,15 +1226,6 @@ static void ept_dump_p2m_table(unsigned char key) >> unsigned long record_counter = 0; >> struct p2m_domain *p2m; >> struct ept_data *ept; >> - static const char memory_types[8][2] = { >> - [0 ... 7] = "?", >> - [MTRR_TYPE_UNCACHABLE] = "UC", >> - [MTRR_TYPE_WRCOMB] = "WC", >> - [MTRR_TYPE_WRTHROUGH] = "WT", >> - [MTRR_TYPE_WRPROT] = "WP", >> - [MTRR_TYPE_WRBACK] = "WB", >> - [MTRR_NUM_TYPES] = "??" >> - }; >> >> for_each_domain(d) >> { >> @@ -1260,8 +1265,8 @@ static void ept_dump_p2m_table(unsigned char key) >> ept_entry->r ? 'r' : ' ', >> ept_entry->w ? 'w' : ' ', >> ept_entry->x ? 'x' : ' ', >> - memory_types[ept_entry->emt][0], >> - memory_types[ept_entry->emt][1] >> + memory_type_to_str(ept_entry->emt)[0], >> + memory_type_to_str(ept_entry->emt)[1] >> ?: ept_entry->emt + '0', >> c ?: ept_entry->ipat ? '!' : ' '); > There's actually a bug here, which I think is worth fixing at once: > The default initializer was a string of length 1, resulting in a > premature NUL character to get placed into the fully expanded > string, causing - afaict - truncation of the intended message. I > therefore think the default string should be e.g. "? ". The code is very opaque. However, that appears to be precisely how it is intended to work. (Having said that - it is your code from c/s 90e9c95f). The following line will only format the raw emt value as a number if there is a NUL character returned from memory_type_to_str(). Putting a space in instead would break this. ~Andrew