From: Ammar Faizi <ammarfaizi2@xxxxxxxxxxx> This commit adds getpagesize() function implementation. The getpagesize() syscall doesn't always exist on the Linux syscall table. Only specific architectures have this syscall. Implementation detail: Some architectures use a fixed page size, like x86. We can hard-code the page size value on such architectures. Some other architectures may use different page sizes. For example, Linux aarch64 supports three values of page size: 4K, 16K, and 64K which are selected at kernel compilation time. The kernel stores the used page size in the auxiliary vector. The auxiliary vector can be obtained from /proc/self/auxv at AT_PAGESZ key-value-pair. /proc/self/auxv is available on all architectures. Once we obtain the page size info, cache the value in a static variable to avoid traversing the auxiliary vector again in the next getpagesize() call. The page size should never change during kernel uptime. Link: https://lwn.net/Articles/519085 Link: https://github.com/torvalds/linux/blob/v6.1/fs/binfmt_elf.c#L260 Signed-off-by: Ammar Faizi <ammarfaizi2@xxxxxxxxxxx> --- tools/include/nolibc/sys.h | 114 +++++++++++++++++++++++++++++++++++++ 1 file changed, 114 insertions(+) diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h index ca348939eb50..e9e3640c36e1 100644 --- a/tools/include/nolibc/sys.h +++ b/tools/include/nolibc/sys.h @@ -18,6 +18,7 @@ #include <linux/fs.h> #include <linux/loop.h> #include <linux/time.h> +#include <linux/auxvec.h> #include "arch.h" #include "errno.h" @@ -407,6 +408,119 @@ int getdents64(int fd, struct linux_dirent64 *dirp, int count) return ret; } +/* + * The getpagesize() syscall doesn't always exist on the Linux syscall + * table. Only specific architectures have this syscall. + * + * Implementation detail: + * Some architectures use a fixed page size, like x86. We can hard-code + * the page size value on such architectures. + * + * Some other architectures may use different page sizes. For example, + * Linux aarch64 supports three values of page size: 4K, 16K, and 64K + * which are selected at kernel compilation time. The kernel stores the + * used page size in the auxiliary vector. The auxiliary vector can be + * obtained from /proc/self/auxv at AT_PAGESZ key-val-pair. + * /proc/self/auxv is available on all architectures. + * + * Once we obtain the page size info, cache the value in a static + * variable to avoid traversing the auxiliary vector again in the next + * getpagesize() call. The page size should never change during kernel + * uptime. + * + * Link: https://lwn.net/Articles/519085 + * Link: https://github.com/torvalds/linux/blob/v6.1/fs/binfmt_elf.c#L260 + * + * + * long getpagesize(void); + * + */ + +#if defined(__x86_64__) || defined(__i386__) || defined(__i486__) || defined(__i586__) || defined(__i686__) +__attribute__((unused)) +static inline long getpagesize(void) +{ + /* + * x86 family is always 4K page. Don't bother + * reading the auxiliary vector. + */ + return 4096; +} +#else +static int sys_open(const char *path, int flags, mode_t mode); +static ssize_t sys_read(int fd, void *buf, size_t count); + +/* + * This function works for all architectures. + */ +static long sys_getpagesize(void) +{ + uint64_t buf[2] = {0, 0}; + long ret; + int fd; + + + fd = sys_open("/proc/self/auxv", O_RDONLY, 0); + if (fd < 0) + return fd; + + while (1) { + ssize_t x; + + x = sys_read(fd, buf, sizeof(buf)); + if (x < 0) { + ret = x; + break; + } + + if (__builtin_expect(x == 0, 0)) { + /* + * We've reached the end of the auxiliary + * vector, but can't find the AT_PAGESZ + * entry. + */ + ret = -ENOENT; + break; + } + + /* + * buf[0] is the key. + * buf[1] is the value. + */ + if (buf[0] == AT_PAGESZ) { + ret = buf[1]; + break; + } + } + + sys_close(fd); + return ret; +} + +__attribute__((unused)) +static long getpagesize(void) +{ + static long cached; + long ret; + + /* + * No need to read the auxv for the second + * getpagesize() call. + */ + if (__builtin_expect(cached != 0, 1)) + return cached; + + ret = sys_getpagesize(); + if (ret < 0) { + SET_ERRNO(-ret); + ret = -1; + } else { + cached = ret; + } + return ret; +} +#endif + /* * pid_t getpgid(pid_t pid); -- Ammar Faizi
