[PATCH] gdb/x86: Fix `-Wstrict-overflow' build error in `i387_collect_xsave'

["Maciej W. Rozycki" <macro@mips.com>]

Make `i' defined within `i387_collect_xsave' unsigned, removing a 
`-Werror=strict-overflow' compilation error:

.../gdb/i387-tdep.c: In function 'void i387_collect_xsave(const regcache*, int, void*, int)':
.../gdb/i387-tdep.c:1348:1: error: assuming signed overflow does not occur when assuming that (X + c) < X is always false [-Werror=strict-overflow]
 i387_collect_xsave (const struct regcache *regcache, int regnum,
 ^
cc1plus: all warnings being treated as errors
Makefile:1610: recipe for target 'i387-tdep.o' failed
make: *** [i387-tdep.o] Error 1

seen with GCC 5.4.0, a commit 8ee22052f690 ("gdb/x86: Handle kernels 
using compact xsave format") regression.  While `regnum' can be -1 on 
entry to the function, to mean all registers, `i' is only used with 
non-negative register numbers.

	gdb/
	* i387-tdep.c (i387_collect_xsave): Make `i' unsigned.
---
Hi,

 I believe this comes from register numbers being retrieved from the 
`tdep' structure at run time and therefore making the compiler unable to 
statically determine in loop expression processing that the calculations 
made on `i' will not cause a signed overflow.

 NB the error message pointing at the function definition rather than the 
declaration of `i' makes it rather difficult to determine what the actual 
cause might be.  I just hope it's only a peculiarity of the somewhat older 
version of the compiler and it has been fixed since.  Could someone from 
the GCC mailing list please comment on that?

 OK to apply?

  Maciej
---
 gdb/i387-tdep.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

gdb-i387-collect-xsave-signed-overflow.diff
Index: gdb/gdb/i387-tdep.c
===================================================================
--- gdb.orig/gdb/i387-tdep.c	2018-05-10 22:13:05.000000000 +0100
+++ gdb/gdb/i387-tdep.c	2018-05-13 23:27:46.194412211 +0100
@@ -1354,7 +1354,7 @@ i387_collect_xsave (const struct regcach
   gdb_byte *p, *regs = (gdb_byte *) xsave;
   gdb_byte raw[I386_MAX_REGISTER_SIZE];
   ULONGEST initial_xstate_bv, clear_bv, xstate_bv = 0;
-  int i;
+  unsigned int i;
   enum
     {
       x87_ctrl_or_mxcsr = 0x1,