If currently two unsigned values are compared via `a - b`, in the case b
is actually bigger than a, the result will not be an negative number (as
-1 is expected) but a huge positive number as the subtraction is an
unsigned subtraction.
Avoid over-/underflow affected operations; use comparisons.
Modern compilers will generate sane code, like:
xor eax, eax
cmp rdi, rsi
seta al
sbb eax, 0
ret
man:sysconf(3) states:
The values obtained from these functions are system configuration constants.
They do not change during the lifetime of a process.
When building on a 32-bit system, the compiler warned that the
following line uses a constant whose value is the overflow result
of a compile-time computation:
Process.c (line 109): } else if (number < 10000 * ONE_M) {
Namely, this constant expression:
10000 * ONE_M
was intended to produce the following value:
10485760000
However, the result overflowed to produce:
1895825408
The reason for this overflow is as follows:
o The macros are expanded:
10000 * (ONE_K * ONE_K)
10000 * (1024L * 1024L)
o The untyped constant expression "10000" is typed:
10000U * (1024L * 1024L)
o The parenthesized expression is evaluated:
10000U * (1048576L)
o The left operand ("10000U") is converted:
10000L * (1048576L)
Unbound by integer sizes, that last multiplication
would produce the following value:
10485760000
However, on a 32-bit machine, where a long is 32 bits
(really 31 bits when talking about positive numbers),
the maximum value that can be computed is 2**31-1:
2147483647
Consequently, the computation overflows.
o The compiler produces a long int value that is the
the result of overflow (10485760000 % 2**31):
1895825408L
Actually, I think this overflow is implementation-defined,
so it's not even a portable description of what happens.
The solution is to use a long long int (or, even better,
an unsigned long long int) type for the constant expression;
the C standard mandates a sufficiently large maximum value
for such types.
Hence, the following change is made to the bad line:
- } else if (number < 10000 * ONE_M) {
+ } else if (number < 10000ULL * ONE_M) {
However, the whole line is now patently silly, because the
variable "number" is typed "unsigned long", and so it will
always be less than the constant expression (the compiler
will warn about this, too).
Hence, "number" must be typed "unsigned long long"; however,
this necessitates changing all of the string formats from
something like "%lu" to something like "%llu".
Et voila! This commit is born.
Then, for the sake of completeness, the declared types of the
constant-expression macros are updated:
o ONE_K is made unsigned (a "UL" instead of "L")
o ONE_T is computed by introducing "1ULL *"
o Similar changes are made for ONE_DECIMAL_{K,T}
Also, a non-portable overflow-conversion to a signed value
has been replaced with a portable comparison:
- if ((long long) number == -1LL) {
+ if (number == ULLONG_MAX) {
It might be worth reviewing the rest of the code for other
cases where overflows are not handled correctly; even at
runtime, it's often necessary to check for overflow unless
such behavior is expected (especially for signed integer
values, for which overflow has implementation-defined
behavior).
PR htop-dev/htop#70 got rid of the infrastructure for generating header
files, but it left behind some code duplication.
Some of cases are things that belong in the header file and don't need
to be repeated in the C file. Other cases are things that belong in the
C file and don't need to be in the header file.
In this commit I tried to fix all of these that I could find. When given
a choice I preferred keeping things out of the header file, unless they
were being used by someone else.
Reasoning:
- implementation was unsound -- broke down when I added a fairly
basic macro definition expanding to a struct initializer in a *.c
file.
- made it way too easy (e.g. via otherwise totally innocuous git
commands) to end up with timestamps such that it always ran
MakeHeader.py but never used its output, leading to overbuild noise
when running what should be a null 'make'.
- but mostly: it's just an awkward way of dealing with C code.
Promote the Arg union to a core data type in Object.c such
that it is visible everywhere (many source files need it),
and correct declarations of several functions that use it.
The Process_sendSignal function is also corrected to have
the expected return type (bool, not void) - an error being
masked by ignoring this not-quite-harmless warning. I've
also added error checking to the kill(2) call here, which
was previously overlooked / missing (?).
A logic mistake in pull request #746 causes <sys/sysmacro.h> to be
*not* included when AC_HEADER_MAJOR (before autoconf-2.70) finds
'major' in <sys/types.h>. Though this would still build htop, it would
still bring deprecation warning in systems using glibc 2.25-2.27. Fix
the logic and suppress the warning.
Also, include config.h in Process.c for the sake of strengthening the
code.
Signed-off-by: Kang-Che Sung <explorer09@gmail.com>
Christian Göttsche