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

[Chen Gang <gang dot chen dot 5i5j at gmail dot com>]

On 10/13/14 23:16, Mark Kettenis wrote:
>> 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.
> 

Excuse me, I do not dare to complain it to gcc members, because for me,
the compiler's printing is obviously, and proofs itself is correct. If I
ask a quite obvious question to them, I guess, I will be complained.

Hmm... But I may have an additional trying: Use original gcc and provide
"-Werror=strict-overflow" to see what will happen.

 - If it will report warning too, I can ask gcc members why integrate
   "-Wstrict-overflow" to -Wall.

 - If it will not report warning, it means original gcc also integrate
   "-Wstrict-overflow" or have no this option. And for me, I prefer to
   use "#pragma GCC diagnostic ignored ... " for our code.

Thanks.

>>   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)
>>

-- 
Chen Gang

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