Messages in this thread Patch in this message | | | From | Andy Shevchenko <> | Date | Wed, 4 Sep 2019 19:19:25 +0300 | Subject | Re: [PATCH] printf: add support for printing symbolic error codes |
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On Sat, Aug 31, 2019 at 12:48 AM Rasmus Villemoes <linux@rasmusvillemoes.dk> wrote: > > It has been suggested several times to extend vsnprintf() to be able > to convert the numeric value of ENOSPC to print "ENOSPC". This is yet > another attempt. Rather than adding another %p extension, simply teach > plain %p to convert ERR_PTRs. While the primary use case is > > if (IS_ERR(foo)) { > pr_err("Sorry, can't do that: %p\n", foo); > return PTR_ERR(foo); > } > > it is also more helpful to get a symbolic error code (or, worst case, > a decimal number) in case an ERR_PTR is accidentally passed to some > %p<something>, rather than the (efault) that check_pointer() would > result in. > > With my embedded hat on, I've made it possible to remove this. > > I've tested that the #ifdeffery in errcode.c is sufficient to make > this compile on arm, arm64, mips, powerpc, s390, x86 - I'm sure the > 0day bot will tell me which ones I've missed. > > The symbols to include have been found by massaging the output of > > find arch include -iname 'errno*.h' | xargs grep -E 'define\s*E' > > In the cases where some common aliasing exists > (e.g. EAGAIN=EWOULDBLOCK on all platforms, EDEADLOCK=EDEADLK on most), > I've moved the more popular one (in terms of 'git grep -w Efoo | wc) > to the bottom so that one takes precedence.
> +/* > + * Ensure these tables to not accidentally become gigantic if some > + * huge errno makes it in. On most architectures, the first table will > + * only have about 140 entries, but mips and parisc have more sparsely > + * allocated errnos (with EHWPOISON = 257 on parisc, and EDQUOT = 1133 > + * on mips), so this wastes a bit of space on those - though we > + * special case the EDQUOT case. > + */ > +#define E(err) [err + BUILD_BUG_ON_ZERO(err <= 0 || err > 300)] = #err
Hmm... Perhaps better to define the upper boundary with something like
#define __E_POSIX_UPPER_BOUNDARY 300 // name sucks, I know
> +#define E(err) [err - 512 + BUILD_BUG_ON_ZERO(err < 512 || err > 550)] = #err
Similar to 550?
> +const char *errcode(int err) > +{ > + /* Might as well accept both -EIO and EIO. */ > + if (err < 0) > + err = -err; > + if (err <= 0) /* INT_MIN or 0 */ > + return NULL; > + if (err < ARRAY_SIZE(codes_0)) > + return codes_0[err]; > + if (err >= 512 && err - 512 < ARRAY_SIZE(codes_512)) > + return codes_512[err - 512]; > + /* But why? */ > + if (IS_ENABLED(CONFIG_MIPS) && err == EDQUOT) /* 1133 */ > + return "EDQUOT";
Another possibility is to initialize the errors at run time with radix tree.
> + return NULL; > +}
> @@ -2111,6 +2112,31 @@ static noinline_for_stack > char *pointer(const char *fmt, char *buf, char *end, void *ptr, > struct printf_spec spec) > { > + /* %px means the user explicitly wanted the pointer formatted as a hex value. */ > + if (*fmt == 'x') > + return pointer_string(buf, end, ptr, spec);
But instead of breaking switch case apart can we use...
> + > + /* If it's an ERR_PTR, try to print its symbolic representation. */ > + if (IS_ERR(ptr)) {
... if (IS_ERR() && *fmt != 'x') { here?
> + long err = PTR_ERR(ptr); > + const char *sym = errcode(-err); > + if (sym) > + return string_nocheck(buf, end, sym, spec); > + /* > + * Funky, somebody passed ERR_PTR(-1234) or some other > + * non-existing Efoo - or more likely > + * CONFIG_SYMBOLIC_ERRCODE=n. None of the > + * %p<something> extensions can make any sense of an > + * ERR_PTR(), and if this was just a plain %p, the > + * user is still better off getting the decimal > + * representation rather than the hash value that > + * ptr_to_id() would generate. > + */ > + spec.flags |= SIGN; > + spec.base = 10; > + return number(buf, end, err, spec); > + }
-- With Best Regards, Andy Shevchenko
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