[gcc r13-1644] [Ada] Fix 0-sized secondary stack allocations

[gcc r13-1644] [Ada] Fix 0-sized secondary stack allocations

[Pierre-Marie de Rodat]

https://gcc.gnu.org/g:6e3c2ee1d17a45eaf2095d4f64462da0993b881e

commit r13-1644-g6e3c2ee1d17a45eaf2095d4f64462da0993b881e
Author: Marc Poulhiès <poulhies@adacore.com>
Date:   Thu Jun 30 09:50:02 2022 +0200

    [Ada] Fix 0-sized secondary stack allocations
    
    The Has_Enough_Free_Memory was not correctly reporting a completely full
    chunk in the case of a 0-sized allocation.
    
    gcc/ada/
    
            * libgnat/s-secsta.adb (Has_Enough_Free_Memory): Check for full
            chunk before computing the available size.

Diff:
---
 gcc/ada/libgnat/s-secsta.adb | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/gcc/ada/libgnat/s-secsta.adb b/gcc/ada/libgnat/s-secsta.adb
index 24b7601c4b5..359e9403339 100644
--- a/gcc/ada/libgnat/s-secsta.adb
+++ b/gcc/ada/libgnat/s-secsta.adb
@@ -506,12 +506,17 @@ package body System.Secondary_Stack is
       Mem_Size : Memory_Size) return Boolean
    is
    begin
+      --  First check if the chunk is full (Byte is > Memory'Last in that
+      --  case), then check there is enough free memory.
+
       --  Byte - 1 denotes the last occupied byte. Subtracting that byte from
       --  the memory capacity of the chunk yields the size of the free memory
       --  within the chunk. The chunk can fit the request as long as the free
       --  memory is as big as the request.
 
-      return Chunk.Size - (Byte - 1) >= Mem_Size;
+      return Chunk.Memory'Last >= Byte
+        and then Chunk.Size - (Byte - 1) >= Mem_Size;
+
    end Has_Enough_Free_Memory;
 
    ----------------------