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[88.21.201.17]) by smtp.gmail.com with ESMTPSA id h13sm15895299wmq.29.2021.03.22.06.15.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 22 Mar 2021 06:15:27 -0700 (PDT) Subject: Re: [PATCH] optionrom/pvh: use memcmp() to find the RSDP signature To: Stefano Garzarella , Paolo Bonzini References: <20210322114834.166798-1-sgarzare@redhat.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: <38e9c458-f931-1fa7-3070-8c2d90b543de@redhat.com> Date: Mon, 22 Mar 2021 14:15:26 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210322114834.166798-1-sgarzare@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 3/22/21 12:48 PM, Stefano Garzarella wrote: > New versions of gcc report a potential error and there may be alignment > issues using uint64_t pointer to check the RSDP signature: > > gcc 10.2.1 "cc (Alpine 10.2.1_pre2) 10.2.1 20210313" reports: > > pc-bios/optionrom/pvh_main.c: In function 'search_rsdp': > pc-bios/optionrom/pvh_main.c:61:21: warning: comparison is always false > due to limited range of data type [-Wtype-limits] > 61 | if (*rsdp_p == RSDP_SIGNATURE) { > | ^~ > > Let's use memcmp() to get more readable code and avoid these issues. > Since pvh optionrom is baremetal, we use the compiler's __builtin_memcmp. > > Reported-by: Philippe Mathieu-Daudé > Suggested-by: Paolo Bonzini > Signed-off-by: Stefano Garzarella > --- > pc-bios/optionrom/pvh_main.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/pc-bios/optionrom/pvh_main.c b/pc-bios/optionrom/pvh_main.c > index 28e79d7fc4..12202e38c2 100644 > --- a/pc-bios/optionrom/pvh_main.c > +++ b/pc-bios/optionrom/pvh_main.c > @@ -27,7 +27,8 @@ asm (".code32"); /* this code will be executed in protected mode */ > #include "optrom_fw_cfg.h" > #include "../../include/hw/xen/start_info.h" > > -#define RSDP_SIGNATURE 0x2052545020445352LL /* "RSD PTR " */ > +#define RSDP_SIGNATURE "RSD PTR " > +#define RSDP_SIGNATURE_SIZE 8 > #define RSDP_AREA_ADDR 0x000E0000 > #define RSDP_AREA_SIZE 0x00020000 > #define EBDA_BASE_ADDR 0x0000040E > @@ -53,12 +54,14 @@ static uint8_t cmdline_buffer[CMDLINE_BUFSIZE]; > /* Search RSDP signature. */ > static uintptr_t search_rsdp(uint32_t start_addr, uint32_t end_addr) > { > - uint64_t *rsdp_p; > + char rsdp_signature[RSDP_SIGNATURE_SIZE] = RSDP_SIGNATURE; static const? > + char *rsdp_p; > > /* RSDP signature is always on a 16 byte boundary */ > - for (rsdp_p = (uint64_t *)start_addr; rsdp_p < (uint64_t *)end_addr; > - rsdp_p += 2) { > - if (*rsdp_p == RSDP_SIGNATURE) { > + for (rsdp_p = (char *)start_addr; rsdp_p < (char *)end_addr; > + rsdp_p += 16) { > + if (__builtin_memcmp(rsdp_p, rsdp_signature, > + RSDP_SIGNATURE_SIZE) == 0) { > return (uintptr_t)rsdp_p; > } > } >