[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PATCH] optionrom/pvh: use memcmp() to find the RSDP signature
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [PATCH] optionrom/pvh: use memcmp() to find the RSDP signature |
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 |
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 <philmd@redhat.com>
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
> 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;
> }
> }
>