Re: [PATCH v2] gdb/i387-tdep.c: Avoid warning for "-Werror=strict-overflow"

[Mark Kettenis <mark dot kettenis at xs4all dot nl>]

> Date: Sun, 12 Oct 2014 21:28:40 +0800
> From: Chen Gang <gang.chen.5i5j@gmail.com>
> 
> gdb requires "-Werror", and I387_ST0_REGNUM (tdep) is 'variable', then
> compiler can think that I387_ST0_REGNUM (tdep) may be a large number,
> which may cause issue, so report warning.
> 
> Need fix this warning, and still keep the code clear enough for readers.
> The related warning under Darwin with gnu built gcc:

Sorry, I disagree with this approach.  I think your compiler is really
being unhelpful here.  See if a newer GCC version of the compiler
still triggers that warning.  If so, complain to the GCC people.

>   gcc -g -O2   -I. -I../../binutils-gdb/gdb -I../../binutils-gdb/gdb/common -I../../binutils-gdb/gdb/config -DLOCALEDIR="\"/usr/local/share/locale\"" -DHAVE_CONFIG_H -I../../binutils-gdb/gdb/../include/opcode -I../../binutils-gdb/gdb/../opcodes/..  -I../../binutils-gdb/gdb/../readline/.. -I../bfd -I../../binutils-gdb/gdb/../bfd -I../../binutils-gdb/gdb/../include -I../libdecnumber -I../../binutils-gdb/gdb/../libdecnumber -I../../binutils-gdb/gdb/gnulib/import -Ibuild-gnulib/import   -DTUI=1 -D_THREAD_SAFE -I/usr/local/Cellar/guile/2.0.11/include/guile/2.0 -I/usr/local/Cellar/gmp/6.0.0a/include -I/usr/local/Cellar/readline/6.3.5/include -I/usr/local/Cellar/bdw-gc/7.2e/include -I/System/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -I/System/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -Wall -Wdeclaration-after-statement -Wpointer-arith -Wpointer-sign -Wno-unused -Wunused-value -Wunused-function -Wno-switch -Wno-char-subscripts -Wmi!
 ssing-protot
> ypes -Wdeclaration-after-statement -Wempty-body -Wmissing-parameter-type -Wold-style-declaration -Wold-style-definition -Wformat-nonliteral -Werror -c -o i387-tdep.o -MT i387-tdep.o -MMD -MP -MF .deps/i387-tdep.Tpo ../../binutils-gdb/gdb/i387-tdep.c
>   ../../binutils-gdb/gdb/i387-tdep.c: In function 'i387_supply_fsave':
>   ../../binutils-gdb/gdb/i387-tdep.c:447:1: error: assuming signed overflow does not occur when assuming that (X + c) >= X is always true [-Werror=strict-overflow]
>    i387_supply_fsave (struct regcache *regcache, int regnum, const void *fsave)
>    ^
>   ../../binutils-gdb/gdb/i387-tdep.c: In function 'i387_collect_fsave':
>   ../../binutils-gdb/gdb/i387-tdep.c:502:1: error: assuming signed overflow does not occur when assuming that (X + c) >= X is always true [-Werror=strict-overflow]
>    i387_collect_fsave (const struct regcache *regcache, int regnum, void *fsave)
>    ^
>   cc1: all warnings being treated as errors
> 
> 2014-10-13  Chen Gang  <gang.chen.5i5j@gmail.com>
> 
> 	* i387-tdep.c (i387_supply_fsave): Avoid warning for
> 	"-Werror=strict-overflow"
> ---
>  gdb/i387-tdep.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/gdb/i387-tdep.c b/gdb/i387-tdep.c
> index d66ac6a..609b5be 100644
> --- a/gdb/i387-tdep.c
> +++ b/gdb/i387-tdep.c
> @@ -450,11 +450,12 @@ i387_supply_fsave (struct regcache *regcache, int regnum, const void *fsave)
>    struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
>    enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
>    const gdb_byte *regs = fsave;
> -  int i;
> +  int i, end;
>  
>    gdb_assert (tdep->st0_regnum >= I386_ST0_REGNUM);
>  
> -  for (i = I387_ST0_REGNUM (tdep); i < I387_XMM0_REGNUM (tdep); i++)
> +  end = I387_XMM0_REGNUM (tdep); /* -Werror=strict-overflow for (X + c) >= X */
> +  for (i = I387_ST0_REGNUM (tdep); i < end; i++)
>      if (regnum == -1 || regnum == i)
>        {
>  	if (fsave == NULL)
> @@ -503,11 +504,12 @@ i387_collect_fsave (const struct regcache *regcache, int regnum, void *fsave)
>  {
>    struct gdbarch_tdep *tdep = gdbarch_tdep (get_regcache_arch (regcache));
>    gdb_byte *regs = fsave;
> -  int i;
> +  int i, end;
>  
>    gdb_assert (tdep->st0_regnum >= I386_ST0_REGNUM);
>  
> -  for (i = I387_ST0_REGNUM (tdep); i < I387_XMM0_REGNUM (tdep); i++)
> +  end = I387_XMM0_REGNUM (tdep); /* -Werror=strict-overflow for (X + c) >= X */
> +  for (i = I387_ST0_REGNUM (tdep); i < end; i++)
>      if (regnum == -1 || regnum == i)
>        {
>  	/* Most of the FPU control registers occupy only 16 bits in
> -- 
> 1.8.5.2 (Apple Git-48)
>