KVM: selftests: Add guest_snprintf() to KVM selftests

Add a local version of guest_snprintf() for use in the guest.

Having a local copy allows the guest access to string formatting
options without dependencies on LIBC.  LIBC is problematic because
it heavily relies on both AVX-512 instructions and a TLS, neither of
which are guaranteed to be set up in the guest.

The file guest_sprintf.c was lifted from arch/x86/boot/printf.c and
adapted to work in the guest, including the addition of buffer length.
I.e. s/sprintf/snprintf/

The functions where prefixed with "guest_" to allow guests to
explicitly call them.

A string formatted by this function is expected to succeed or die.  If
something goes wrong during the formatting process a GUEST_ASSERT()
will be thrown.

Signed-off-by: Aaron Lewis <aaronlewis@google.com>
Link: https://lore.kernel.org/all/mtdi6smhur5rqffvpu7qux7mptonw223y2653x2nwzvgm72nlo@zyc4w3kwl3rg
[sean: add a link to the discussion of other options]
Link: https://lore.kernel.org/r/20230729003643.1053367-6-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index f6c14ab..f65889f 100644 (file)
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -23,6 +23,7 @@ LIBKVM += lib/guest_modes.c
 LIBKVM += lib/io.c
 LIBKVM += lib/kvm_util.c
 LIBKVM += lib/memstress.c
+LIBKVM += lib/guest_sprintf.c
 LIBKVM += lib/rbtree.c
 LIBKVM += lib/sparsebit.c
 LIBKVM += lib/test_util.c

diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h
index a4bea44..7a5907d 100644 (file)
--- a/tools/testing/selftests/kvm/include/test_util.h
+++ b/tools/testing/selftests/kvm/include/test_util.h
@@ -185,4 +185,7 @@ static inline uint32_t atoi_non_negative(const char *name, const char *num_str)
        return num;
 }
 
+int guest_vsnprintf(char *buf, int n, const char *fmt, va_list args);
+int guest_snprintf(char *buf, int n, const char *fmt, ...);
+
 #endif /* SELFTEST_KVM_TEST_UTIL_H */

diff --git a/tools/testing/selftests/kvm/lib/guest_sprintf.c b/tools/testing/selftests/kvm/lib/guest_sprintf.c
new file mode 100644 (file)
index 0000000..c4a69d8
--- /dev/null
+++ b/tools/testing/selftests/kvm/lib/guest_sprintf.c
@@ -0,0 +1,307 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include "test_util.h"
+#include "kvm_util.h"
+#include "ucall_common.h"
+
+#define APPEND_BUFFER_SAFE(str, end, v) \
+do {                                   \
+       GUEST_ASSERT(str < end);        \
+       *str++ = (v);                   \
+} while (0)
+
+static int isdigit(int ch)
+{
+       return (ch >= '0') && (ch <= '9');
+}
+
+static int skip_atoi(const char **s)
+{
+       int i = 0;
+
+       while (isdigit(**s))
+               i = i * 10 + *((*s)++) - '0';
+       return i;
+}
+
+#define ZEROPAD        1               /* pad with zero */
+#define SIGN   2               /* unsigned/signed long */
+#define PLUS   4               /* show plus */
+#define SPACE  8               /* space if plus */
+#define LEFT   16              /* left justified */
+#define SMALL  32              /* Must be 32 == 0x20 */
+#define SPECIAL        64              /* 0x */
+
+#define __do_div(n, base)                              \
+({                                                     \
+       int __res;                                      \
+                                                       \
+       __res = ((uint64_t) n) % (uint32_t) base;       \
+       n = ((uint64_t) n) / (uint32_t) base;           \
+       __res;                                          \
+})
+
+static char *number(char *str, const char *end, long num, int base, int size,
+                   int precision, int type)
+{
+       /* we are called with base 8, 10 or 16, only, thus don't need "G..."  */
+       static const char digits[16] = "0123456789ABCDEF"; /* "GHIJKLMNOPQRSTUVWXYZ"; */
+
+       char tmp[66];
+       char c, sign, locase;
+       int i;
+
+       /*
+        * locase = 0 or 0x20. ORing digits or letters with 'locase'
+        * produces same digits or (maybe lowercased) letters
+        */
+       locase = (type & SMALL);
+       if (type & LEFT)
+               type &= ~ZEROPAD;
+       if (base < 2 || base > 16)
+               return NULL;
+       c = (type & ZEROPAD) ? '0' : ' ';
+       sign = 0;
+       if (type & SIGN) {
+               if (num < 0) {
+                       sign = '-';
+                       num = -num;
+                       size--;
+               } else if (type & PLUS) {
+                       sign = '+';
+                       size--;
+               } else if (type & SPACE) {
+                       sign = ' ';
+                       size--;
+               }
+       }
+       if (type & SPECIAL) {
+               if (base == 16)
+                       size -= 2;
+               else if (base == 8)
+                       size--;
+       }
+       i = 0;
+       if (num == 0)
+               tmp[i++] = '0';
+       else
+               while (num != 0)
+                       tmp[i++] = (digits[__do_div(num, base)] | locase);
+       if (i > precision)
+               precision = i;
+       size -= precision;
+       if (!(type & (ZEROPAD + LEFT)))
+               while (size-- > 0)
+                       APPEND_BUFFER_SAFE(str, end, ' ');
+       if (sign)
+               APPEND_BUFFER_SAFE(str, end, sign);
+       if (type & SPECIAL) {
+               if (base == 8)
+                       APPEND_BUFFER_SAFE(str, end, '0');
+               else if (base == 16) {
+                       APPEND_BUFFER_SAFE(str, end, '0');
+                       APPEND_BUFFER_SAFE(str, end, 'x');
+               }
+       }
+       if (!(type & LEFT))
+               while (size-- > 0)
+                       APPEND_BUFFER_SAFE(str, end, c);
+       while (i < precision--)
+               APPEND_BUFFER_SAFE(str, end, '0');
+       while (i-- > 0)
+               APPEND_BUFFER_SAFE(str, end, tmp[i]);
+       while (size-- > 0)
+               APPEND_BUFFER_SAFE(str, end, ' ');
+
+       return str;
+}
+
+int guest_vsnprintf(char *buf, int n, const char *fmt, va_list args)
+{
+       char *str, *end;
+       const char *s;
+       uint64_t num;
+       int i, base;
+       int len;
+
+       int flags;              /* flags to number() */
+
+       int field_width;        /* width of output field */
+       int precision;          /*
+                                * min. # of digits for integers; max
+                                * number of chars for from string
+                                */
+       int qualifier;          /* 'h', 'l', or 'L' for integer fields */
+
+       end = buf + n;
+       GUEST_ASSERT(buf < end);
+       GUEST_ASSERT(n > 0);
+
+       for (str = buf; *fmt; ++fmt) {
+               if (*fmt != '%') {
+                       APPEND_BUFFER_SAFE(str, end, *fmt);
+                       continue;
+               }
+
+               /* process flags */
+               flags = 0;
+repeat:
+               ++fmt;          /* this also skips first '%' */
+               switch (*fmt) {
+               case '-':
+                       flags |= LEFT;
+                       goto repeat;
+               case '+':
+                       flags |= PLUS;
+                       goto repeat;
+               case ' ':
+                       flags |= SPACE;
+                       goto repeat;
+               case '#':
+                       flags |= SPECIAL;
+                       goto repeat;
+               case '0':
+                       flags |= ZEROPAD;
+                       goto repeat;
+               }
+
+               /* get field width */
+               field_width = -1;
+               if (isdigit(*fmt))
+                       field_width = skip_atoi(&fmt);
+               else if (*fmt == '*') {
+                       ++fmt;
+                       /* it's the next argument */
+                       field_width = va_arg(args, int);
+                       if (field_width < 0) {
+                               field_width = -field_width;
+                               flags |= LEFT;
+                       }
+               }
+
+               /* get the precision */
+               precision = -1;
+               if (*fmt == '.') {
+                       ++fmt;
+                       if (isdigit(*fmt))
+                               precision = skip_atoi(&fmt);
+                       else if (*fmt == '*') {
+                               ++fmt;
+                               /* it's the next argument */
+                               precision = va_arg(args, int);
+                       }
+                       if (precision < 0)
+                               precision = 0;
+               }
+
+               /* get the conversion qualifier */
+               qualifier = -1;
+               if (*fmt == 'h' || *fmt == 'l' || *fmt == 'L') {
+                       qualifier = *fmt;
+                       ++fmt;
+               }
+
+               /* default base */
+               base = 10;
+
+               switch (*fmt) {
+               case 'c':
+                       if (!(flags & LEFT))
+                               while (--field_width > 0)
+                                       APPEND_BUFFER_SAFE(str, end, ' ');
+                       APPEND_BUFFER_SAFE(str, end,
+                                           (uint8_t)va_arg(args, int));
+                       while (--field_width > 0)
+                               APPEND_BUFFER_SAFE(str, end, ' ');
+                       continue;
+
+               case 's':
+                       s = va_arg(args, char *);
+                       len = strnlen(s, precision);
+
+                       if (!(flags & LEFT))
+                               while (len < field_width--)
+                                       APPEND_BUFFER_SAFE(str, end, ' ');
+                       for (i = 0; i < len; ++i)
+                               APPEND_BUFFER_SAFE(str, end, *s++);
+                       while (len < field_width--)
+                               APPEND_BUFFER_SAFE(str, end, ' ');
+                       continue;
+
+               case 'p':
+                       if (field_width == -1) {
+                               field_width = 2 * sizeof(void *);
+                               flags |= SPECIAL | SMALL | ZEROPAD;
+                       }
+                       str = number(str, end,
+                                    (uint64_t)va_arg(args, void *), 16,
+                                    field_width, precision, flags);
+                       continue;
+
+               case 'n':
+                       if (qualifier == 'l') {
+                               long *ip = va_arg(args, long *);
+                               *ip = (str - buf);
+                       } else {
+                               int *ip = va_arg(args, int *);
+                               *ip = (str - buf);
+                       }
+                       continue;
+
+               case '%':
+                       APPEND_BUFFER_SAFE(str, end, '%');
+                       continue;
+
+               /* integer number formats - set up the flags and "break" */
+               case 'o':
+                       base = 8;
+                       break;
+
+               case 'x':
+                       flags |= SMALL;
+               case 'X':
+                       base = 16;
+                       break;
+
+               case 'd':
+               case 'i':
+                       flags |= SIGN;
+               case 'u':
+                       break;
+
+               default:
+                       APPEND_BUFFER_SAFE(str, end, '%');
+                       if (*fmt)
+                               APPEND_BUFFER_SAFE(str, end, *fmt);
+                       else
+                               --fmt;
+                       continue;
+               }
+               if (qualifier == 'l')
+                       num = va_arg(args, uint64_t);
+               else if (qualifier == 'h') {
+                       num = (uint16_t)va_arg(args, int);
+                       if (flags & SIGN)
+                               num = (int16_t)num;
+               } else if (flags & SIGN)
+                       num = va_arg(args, int);
+               else
+                       num = va_arg(args, uint32_t);
+               str = number(str, end, num, base, field_width, precision, flags);
+       }
+
+       GUEST_ASSERT(str < end);
+       *str = '\0';
+       return str - buf;
+}
+
+int guest_snprintf(char *buf, int n, const char *fmt, ...)
+{
+       va_list va;
+       int len;
+
+       va_start(va, fmt);
+       len = guest_vsnprintf(buf, n, fmt, va);
+       va_end(va);
+
+       return len;
+}