Completion of error handling

[elfring]

Would you like to add more error handling for return values from functions like the following?

• fclose ⇒ Settings_write
• fputs ⇒ printVersionFlag

[fasterit]

For sure. The code can use a good makeover for more defensive programming and avoiding of overflows. Patches welcome.

[BenBE]

Having the source compile with the following compiler settings is a good start:

-dP
-pedantic
-Wall
-Wextra
-Werror
-Wunused-parameter
-Wduplicated-cond
-Wduplicated-branches
-Wunreachable-code
-Wshadow # Patches incoming; not much to do though
-Winit-self
-Wrestrict
-Wnull-dereference
-Wpointer-arith
-Wcast-align
-Wfloat-equal
-Wlogical-op
-Wwrite-strings
-Wformat=2
-Wno-error=expansion-to-defined
-Wstrict-overflow=5
-Wconversion # Patches incoming, cf. #78
-Wundef
-Wswitch-default
-Wswitch-enum
-fno-strict-aliasing

[BenBE]

The suggested set of compiler flags build correctly with both #101 and #102 applied.

[BenBE]

As I see some patches coming in using the GCC attributes, I had a look at some of my projects and saw, that one feature that could be interesting in the long run, might be buffer access tracking:

// Allow to use the GCC10 access attribute even with older compilers (by ignoring it if unsupported)
#if !defined(__clang__) && defined(__GNUC__) && (__GNUC__ >= 10)
#define HTOP_CHK_R1(x) __attribute__((access(read_only,x)))
#define HTOP_CHK_RW1(x) __attribute__((access(read_write,x)))
#define HTOP_CHK_W1(x) __attribute__((access(write_only,x)))

#define HTOP_CHK_R(x,y) __attribute__((access(read_only,x,y)))
#define HTOP_CHK_RW(x,y) __attribute__((access(read_write,x,y)))
#define HTOP_CHK_W(x,y) __attribute__((access(write_only,x,y)))
#else
#define HTOP_CHK_R1(x)
#define HTOP_CHK_RW1(x)
#define HTOP_CHK_W1(x)

#define HTOP_CHK_R(x,y)
#define HTOP_CHK_RW(x,y)
#define HTOP_CHK_W(x,y)
#endif

Basically what these attributes do (applied to a function declaration) is mark the argument at location x to contain a pointer to y items of the type that the argument at index x points to.

Example:

__attribute__((access(read_only,1,2)))
__attribute__((nonnull(1)))
void foo(const uint8_t* buf, size_t bufsize) {
    // …
    uint8_t bar = buf[bufsize]; // <- Throws warning
    // …
}

Using the nonnull attribute here also allows to skip the NULL check, as the compiler ensures this can't be NULL when this function is called.