[gcc(refs/users/guojiufu/heads/personal-branch)] [Ada] Avoid buffer overflow in Long_Long_Float_Text_IO

[Jiu Fu Guo]

https://gcc.gnu.org/g:b5682bf40cedf95d1e0150c6a6ba7a64c59fd968

commit b5682bf40cedf95d1e0150c6a6ba7a64c59fd968
Author: Steve Baird <baird@adacore.com>
Date:   Fri Jan 17 22:10:13 2020 -0800

    [Ada] Avoid buffer overflow in Long_Long_Float_Text_IO
    
    2020-06-04  Steve Baird  <baird@adacore.com>
    
    gcc/ada/
    
            * libgnat/s-imgrea.ads: Declare a named number
            Max_Real_Image_Length with value 5200.  Provide a comment
            explaining why this value was chosen.
            * libgnat/s-imgrea.adb (Set_Image_Real): Increase the upper
            bound of the local String variable Digs to
            Max_Real_Image_Length.
            * libgnat/a-tiflau.adb (Put): Increase the upper bound of the
            local String variable Buf to Max_Real_Image_Length.
            (Puts): Increase the upper bound of the local String variable
            Buf to Max_Real_Image_Length.

Diff:
---
 gcc/ada/libgnat/a-tiflau.adb |  4 ++--
 gcc/ada/libgnat/s-imgrea.adb | 11 +++--------
 gcc/ada/libgnat/s-imgrea.ads |  5 +++++
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/gcc/ada/libgnat/a-tiflau.adb b/gcc/ada/libgnat/a-tiflau.adb
index 25d78ca8884..214b5c8f2c3 100644
--- a/gcc/ada/libgnat/a-tiflau.adb
+++ b/gcc/ada/libgnat/a-tiflau.adb
@@ -194,7 +194,7 @@ package body Ada.Text_IO.Float_Aux is
       Aft  : Field;
       Exp  : Field)
    is
-      Buf : String (1 .. 3 * Field'Last + 2);
+      Buf : String (1 .. Max_Real_Image_Length);
       Ptr : Natural := 0;
 
    begin
@@ -212,7 +212,7 @@ package body Ada.Text_IO.Float_Aux is
       Aft  : Field;
       Exp  : Field)
    is
-      Buf : String (1 .. 3 * Field'Last + 2);
+      Buf : String (1 .. Max_Real_Image_Length);
       Ptr : Natural := 0;
 
    begin
diff --git a/gcc/ada/libgnat/s-imgrea.adb b/gcc/ada/libgnat/s-imgrea.adb
index 642724b3af7..68b1fdc6ffd 100644
--- a/gcc/ada/libgnat/s-imgrea.adb
+++ b/gcc/ada/libgnat/s-imgrea.adb
@@ -151,14 +151,9 @@ package body System.Img_Real is
       Scale : Integer;
       Expon : Integer;
 
-      Field_Max : constant := 255;
-      --  This should be the same value as Ada.[Wide_]Text_IO.Field'Last.
-      --  It is not worth dragging in Ada.Text_IO to pick up this value,
-      --  since it really should never be necessary to change it.
-
-      Digs : String (1 .. 2 * Field_Max + 16);
-      --  Array used to hold digits of converted integer value. This is a
-      --  large enough buffer to accommodate ludicrous values of Fore and Aft.
+      Digs : String (1 .. Max_Real_Image_Length);
+      --  Array used to hold digits of converted integer value. This is a large
+      --  enough buffer to accommodate ludicrous Fore/Aft/Exp combinations.
 
       Ndigs : Natural;
       --  Number of digits stored in Digs (and also subscript of last digit)
diff --git a/gcc/ada/libgnat/s-imgrea.ads b/gcc/ada/libgnat/s-imgrea.ads
index 8adb6230645..9711516164c 100644
--- a/gcc/ada/libgnat/s-imgrea.ads
+++ b/gcc/ada/libgnat/s-imgrea.ads
@@ -73,4 +73,9 @@ package System.Img_Real is
    --  can be set to any valid values for the case of use from Text_IO. Note
    --  that no space is stored at the start for non-negative values.
 
+   Max_Real_Image_Length : constant := 5200;
+   --   If Exp is set to zero and Aft is set to Text_IO.Field'Last (i.e., 255)
+   --   then Long_Long_Float'Last generates an image whose length is
+   --   slightly less than 5200.
+
 end System.Img_Real;