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digitalmars.D.bugs - [Issue 19128] New: argument to alloca may be too large


          Issue ID: 19128
           Summary: argument to alloca may be too large
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: druntime
          Assignee: nobody puremagic.com
          Reporter: belka caraus.de

In rt.arrayassign._d_arraysetassign alloca is called if the buffer should be
allocated is larger than 16 bytes:

void[16] buf = void;
void[] tmp;
if (element_size > buf.sizeof)
    tmp = alloca(element_size)[0 .. element_size];
    tmp = buf[];

It is dangerous since alloca unavailable to allocate causes undefined
behaviour, so the alloca man page states:

The alloca() function returns a pointer to the beginning of the allocated
space.  If the allocation causes stack overflow, program behavior is undefined.

See related discussion:

Jul 30 2018