[PATCH] Make out of range type conversions explicit

[Pedro Alves]

On 6/30/20 2:58 PM, Gary Benson via Gdb-patches wrote:
> HI all,
> 
> Clang fails to compile two testcases with the following warning:
> implicit conversion from 'X' to 'Y' changes value from x to y
> [-Wconstant-conversion].  This patch adds casts that make the
> value-changing conversions explicit.

It's helpful if you show the full error.  Like:

gdb compile failed, /home/pedro/gdb/mygit/src/gdb/testsuite/gdb.base/charset.c:144:20: warning: 
      implicit conversion from 'int' to 'char' changes value from 162 to -94
      [-Wconstant-conversion]
               11, 162, 17);
                   ^~~
/home/pedro/gdb/mygit/src/gdb/testsuite/gdb.base/charset.c:151:16: warning: 
      implicit conversion from 'int' to 'char' changes value from 167 to -89
      [-Wconstant-conversion]
               167,
               ^~~
/home/pedro/gdb/mygit/src/gdb/testsuite/gdb.base/charset.c:168:16: warning: 
      implicit conversion from 'int' to 'char' changes value from 167 to -89
      [-Wconstant-conversion]
               167,
               ^~~
3 warnings generated.

                === gdb Summary ===

# of untested testcases         1

Above, I think a better fix would be to change init_string to take
unsigned char parameters, since we're really passing down raw bytes.

The other one is:

~~~~~~
gdb compile failed, /home/pedro/gdb/mygit/src/gdb/testsuite/gdb.base/structs2.c:16:14: warning: 
      implicit conversion from 'int' to 'signed char' changes value from 130 to
      -126 [-Wconstant-conversion]
  param_reg (130, 120, 33000, 32000);
  ~~~~~~~~~  ^~~
/home/pedro/gdb/mygit/src/gdb/testsuite/gdb.base/structs2.c:16:24: warning: 
      implicit conversion from 'int' to 'short' changes value from 33000 to
      -32536 [-Wconstant-conversion]
  param_reg (130, 120, 33000, 32000);
  ~~~~~~~~~            ^~~~~
2 warnings generated.
WARNING: Prototypes not supported, rebuilding with -DNO_PROTOTYPES
gdb compile failed, /home/pedro/gdb/mygit/src/gdb/testsuite/gdb.base/structs2.c:16:14: warning: 
      implicit conversion from 'int' to 'signed char' changes value from 130 to
      -126 [-Wconstant-conversion]
  param_reg (130, 120, 33000, 32000);
  ~~~~~~~~~  ^~~
/home/pedro/gdb/mygit/src/gdb/testsuite/gdb.base/structs2.c:16:24: warning: 
      implicit conversion from 'int' to 'short' changes value from 33000 to
      -32536 [-Wconstant-conversion]
  param_reg (130, 120, 33000, 32000);
  ~~~~~~~~~            ^~~~~
2 warnings generated.

                === gdb Summary ===

# of untested testcases         1
~~~~~~

Here, param_reg's prototype is:

 static void param_reg (register signed char pr_char,
 		       register unsigned char pr_uchar,
 		       register short pr_short,
 		       register unsigned short pr_ushort);
 
pr_char and pr_short are signed, so how about just passing
down negative numbers.  That's what the testcase expects
GDB will show:

gdb_test "continue" \
    ".*pr_char=-126.*pr_uchar=120.*pr_short=-32536.*pr_ushort=32000.*bkpt = 1.*" \
    "structs2 continue2"

I think it's best to push fix each testcase in its own commit.

See patches attached.
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