c-c++-common/analyzer/out-of-bounds-diagram-11.c written type vs toolchain

[Joern Wolfgang Rennecke]

On 22/07/2024 17:13, Joern Wolfgang Rennecke wrote:
  > I guess you could reduce the differences between platforms if you 
didn't
> use types as defined by headerfiles directly, as they might be #defines 
> or typedefs or whatever, and instead used your own typedef or struct types.

It seems a typedef to int is seen through, even if you chain two of them 
together.
After preprocessing, newlib has:

typedef long int __int32_t;

typedef __int32_t int32_t ;

So the crucial point seems to be to have 'long int',  but that is of 
course not portable for int32_t.

So to get portable code and consistent messages, I suppose we should use 
a struct:

   typedef struct { int32_t i; } my_int32;
   my_int32 s42 = { 42 };
   my_int32 *buf = (my_int32 *) __builtin_alloca (4 * size + 3); /* { 
dg-warning "allocated buffer size is not a multiple of the pointee's 
size" } */
   buf[size] = s42; /* { dg-warning "stack-based buffer overflow" } */

Now suddenly the diagram is made *more* verbose, with the struct keyword 
added.
                            ┌─────────────────────────────────────────────┐
                            │    write of ‘struct my_int32’ (4 bytes)     │
                            └─────────────────────────────────────────────┘
                                   │                         │
                                   │                         │
                                   v                         v
   ┌───────────────────────────────────────┐     ┌────────────────────────┐
   │   buffer allocated on stack at (1)    │     │   after valid range    │
   └───────────────────────────────────────┘     └────────────────────────┘
   ├───────────────────┬───────────────────┤     ├───────────┬────────────┤
                       │                                     │
      ╭────────────────┴───────────────╮           ╭─────────┴────────╮
      │capacity: ‘(size * 4) + 3’ bytes│           │overflow of 1 byte│
      ╰────────────────────────────────╯           ╰──────────────────╯