efi/printf: Factor out width/precision parsing

Factor out the width/precision parsing into a helper function.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200518190716.751506-12-nivedita@alum.mit.edu
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

diff --git a/drivers/firmware/efi/libstub/vsprintf.c b/drivers/firmware/efi/libstub/vsprintf.c
index b7316ab..0e6f2c1 100644 (file)
--- a/drivers/firmware/efi/libstub/vsprintf.c
+++ b/drivers/firmware/efi/libstub/vsprintf.c
@@ -231,7 +231,20 @@ int get_flags(const char **fmt)
        } while (1);
 }
 
-int vsprintf(char *buf, const char *fmt, va_list args)
+static
+int get_int(const char **fmt, va_list *ap)
+{
+       if (isdigit(**fmt))
+               return skip_atoi(fmt);
+       if (**fmt == '*') {
+               ++(*fmt);
+               /* it's the next argument */
+               return va_arg(*ap, int);
+       }
+       return 0;
+}
+
+int vsprintf(char *buf, const char *fmt, va_list ap)
 {
        int len;
        unsigned long long num;
@@ -246,6 +259,24 @@ int vsprintf(char *buf, const char *fmt, va_list args)
                                   number of chars for from string */
        int qualifier;          /* 'h', 'hh', 'l' or 'll' for integer fields */
 
+       va_list args;
+
+       /*
+        * We want to pass our input va_list to helper functions by reference,
+        * but there's an annoying edge case. If va_list was originally passed
+        * to us by value, we could just pass &ap down to the helpers. This is
+        * the case on, for example, X86_32.
+        * However, on X86_64 (and possibly others), va_list is actually a
+        * size-1 array containing a structure. Our function parameter ap has
+        * decayed from T[1] to T*, and &ap has type T** rather than T(*)[1],
+        * which is what will be expected by a function taking a va_list *
+        * parameter.
+        * One standard way to solve this mess is by creating a copy in a local
+        * variable of type va_list and then passing a pointer to that local
+        * copy instead, which is what we do here.
+        */
+       va_copy(args, ap);
+
        for (str = buf; *fmt; ++fmt) {
                if (*fmt != '%' || *++fmt == '%') {
                        *str++ = *fmt;
@@ -256,32 +287,17 @@ int vsprintf(char *buf, const char *fmt, va_list args)
                flags = get_flags(&fmt);
 
                /* 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;
-                       }
+               field_width = get_int(&fmt, &args);
+               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);
-                       } else {
-                               precision = 0;
-                       }
+                       precision = get_int(&fmt, &args);
                        if (precision >= 0)
                                flags &= ~ZEROPAD;
                }
@@ -392,6 +408,9 @@ int vsprintf(char *buf, const char *fmt, va_list args)
                str = number(str, num, base, field_width, precision, flags);
        }
        *str = '\0';
+
+       va_end(args);
+
        return str - buf;
 }