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Subject[PATCH] printf: add support for printing symbolic error codes
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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.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
include/linux/errcode.h | 14 +++
lib/Kconfig.debug | 8 ++
lib/Makefile | 1 +
lib/errcode.c | 215 ++++++++++++++++++++++++++++++++++++++++
lib/test_printf.c | 14 +++
lib/vsprintf.c | 28 +++++-
6 files changed, 278 insertions(+), 2 deletions(-)
create mode 100644 include/linux/errcode.h
create mode 100644 lib/errcode.c

diff --git a/include/linux/errcode.h b/include/linux/errcode.h
new file mode 100644
index 000000000000..9dc4cfaa37ab
--- /dev/null
+++ b/include/linux/errcode.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_ERRCODE_H
+#define _LINUX_ERRCODE_H
+
+#ifdef CONFIG_SYMBOLIC_ERRCODE
+const char *errcode(int code);
+#else
+static inline const char *errcode(int code)
+{
+ return NULL;
+}
+#endif
+
+#endif /* _LINUX_ERRCODE_H */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 5960e2980a8a..dc1b20872774 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -164,6 +164,14 @@ config DYNAMIC_DEBUG
See Documentation/admin-guide/dynamic-debug-howto.rst for additional
information.

+config SYMBOLIC_ERRCODE
+ bool "Support symbolic error codes in printf"
+ help
+ If you say Y here, the kernel's printf implementation will
+ be able to print symbolic errors such as ENOSPC instead of
+ the number 28. It makes the kernel image slightly larger
+ (about 3KB), but can make the kernel logs easier to read.
+
endmenu # "printk and dmesg options"

menu "Compile-time checks and compiler options"
diff --git a/lib/Makefile b/lib/Makefile
index 29c02a924973..664ecf10ee2a 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -185,6 +185,7 @@ lib-$(CONFIG_GENERIC_BUG) += bug.o
obj-$(CONFIG_HAVE_ARCH_TRACEHOOK) += syscall.o

obj-$(CONFIG_DYNAMIC_DEBUG) += dynamic_debug.o
+obj-$(CONFIG_SYMBOLIC_ERRCODE) += errcode.o

obj-$(CONFIG_NLATTR) += nlattr.o

diff --git a/lib/errcode.c b/lib/errcode.c
new file mode 100644
index 000000000000..7dcf97d5307f
--- /dev/null
+++ b/lib/errcode.c
@@ -0,0 +1,215 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/build_bug.h>
+#include <linux/errno.h>
+#include <linux/errcode.h>
+#include <linux/kernel.h>
+
+/*
+ * 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
+static const char *codes_0[] = {
+ E(E2BIG),
+ E(EACCES),
+ E(EADDRINUSE),
+ E(EADDRNOTAVAIL),
+ E(EADV),
+ E(EAFNOSUPPORT),
+ E(EALREADY),
+ E(EBADE),
+ E(EBADF),
+ E(EBADFD),
+ E(EBADMSG),
+ E(EBADR),
+ E(EBADRQC),
+ E(EBADSLT),
+ E(EBFONT),
+ E(EBUSY),
+#ifdef ECANCELLED
+ E(ECANCELLED),
+#endif
+ E(ECHILD),
+ E(ECHRNG),
+ E(ECOMM),
+ E(ECONNABORTED),
+ E(ECONNRESET),
+ E(EDEADLOCK),
+ E(EDESTADDRREQ),
+ E(EDOM),
+ E(EDOTDOT),
+#ifndef CONFIG_MIPS
+ E(EDQUOT),
+#endif
+ E(EEXIST),
+ E(EFAULT),
+ E(EFBIG),
+ E(EHOSTDOWN),
+ E(EHOSTUNREACH),
+ E(EHWPOISON),
+ E(EIDRM),
+ E(EILSEQ),
+#ifdef EINIT
+ E(EINIT),
+#endif
+ E(EINPROGRESS),
+ E(EINTR),
+ E(EINVAL),
+ E(EIO),
+ E(EISCONN),
+ E(EISDIR),
+ E(EISNAM),
+ E(EKEYEXPIRED),
+ E(EKEYREJECTED),
+ E(EKEYREVOKED),
+ E(EL2HLT),
+ E(EL2NSYNC),
+ E(EL3HLT),
+ E(EL3RST),
+ E(ELIBACC),
+ E(ELIBBAD),
+ E(ELIBEXEC),
+ E(ELIBMAX),
+ E(ELIBSCN),
+ E(ELNRNG),
+ E(ELOOP),
+ E(EMEDIUMTYPE),
+ E(EMFILE),
+ E(EMLINK),
+ E(EMSGSIZE),
+ E(EMULTIHOP),
+ E(ENAMETOOLONG),
+ E(ENAVAIL),
+ E(ENETDOWN),
+ E(ENETRESET),
+ E(ENETUNREACH),
+ E(ENFILE),
+ E(ENOANO),
+ E(ENOBUFS),
+ E(ENOCSI),
+ E(ENODATA),
+ E(ENODEV),
+ E(ENOENT),
+ E(ENOEXEC),
+ E(ENOKEY),
+ E(ENOLCK),
+ E(ENOLINK),
+ E(ENOMEDIUM),
+ E(ENOMEM),
+ E(ENOMSG),
+ E(ENONET),
+ E(ENOPKG),
+ E(ENOPROTOOPT),
+ E(ENOSPC),
+ E(ENOSR),
+ E(ENOSTR),
+#ifdef ENOSYM
+ E(ENOSYM),
+#endif
+ E(ENOSYS),
+ E(ENOTBLK),
+ E(ENOTCONN),
+ E(ENOTDIR),
+ E(ENOTEMPTY),
+ E(ENOTNAM),
+ E(ENOTRECOVERABLE),
+ E(ENOTSOCK),
+ E(ENOTTY),
+ E(ENOTUNIQ),
+ E(ENXIO),
+ E(EOPNOTSUPP),
+ E(EOVERFLOW),
+ E(EOWNERDEAD),
+ E(EPERM),
+ E(EPFNOSUPPORT),
+ E(EPIPE),
+#ifdef EPROCLIM
+ E(EPROCLIM),
+#endif
+ E(EPROTO),
+ E(EPROTONOSUPPORT),
+ E(EPROTOTYPE),
+ E(ERANGE),
+ E(EREMCHG),
+#ifdef EREMDEV
+ E(EREMDEV),
+#endif
+ E(EREMOTE),
+ E(EREMOTEIO),
+#ifdef EREMOTERELEASE
+ E(EREMOTERELEASE),
+#endif
+ E(ERESTART),
+ E(ERFKILL),
+ E(EROFS),
+#ifdef ERREMOTE
+ E(ERREMOTE),
+#endif
+ E(ESHUTDOWN),
+ E(ESOCKTNOSUPPORT),
+ E(ESPIPE),
+ E(ESRCH),
+ E(ESRMNT),
+ E(ESTALE),
+ E(ESTRPIPE),
+ E(ETIME),
+ E(ETIMEDOUT),
+ E(ETOOMANYREFS),
+ E(ETXTBSY),
+ E(EUCLEAN),
+ E(EUNATCH),
+ E(EUSERS),
+ E(EXDEV),
+ E(EXFULL),
+
+ E(ECANCELED),
+ E(EAGAIN), /* EWOULDBLOCK */
+ E(ECONNREFUSED), /* EREFUSED */
+ E(EDEADLK), /* EDEADLK */
+};
+#undef E
+
+#define E(err) [err - 512 + BUILD_BUG_ON_ZERO(err < 512 || err > 550)] = #err
+static const char *codes_512[] = {
+ E(ERESTARTSYS),
+ E(ERESTARTNOINTR),
+ E(ERESTARTNOHAND),
+ E(ENOIOCTLCMD),
+ E(ERESTART_RESTARTBLOCK),
+ E(EPROBE_DEFER),
+ E(EOPENSTALE),
+ E(ENOPARAM),
+
+ E(EBADHANDLE),
+ E(ENOTSYNC),
+ E(EBADCOOKIE),
+ E(ENOTSUPP),
+ E(ETOOSMALL),
+ E(ESERVERFAULT),
+ E(EBADTYPE),
+ E(EJUKEBOX),
+ E(EIOCBQUEUED),
+ E(ERECALLCONFLICT),
+};
+#undef E
+
+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";
+ return NULL;
+}
diff --git a/lib/test_printf.c b/lib/test_printf.c
index 944eb50f3862..0401a2341245 100644
--- a/lib/test_printf.c
+++ b/lib/test_printf.c
@@ -212,6 +212,7 @@ test_string(void)
#define PTR_STR "ffff0123456789ab"
#define PTR_VAL_NO_CRNG "(____ptrval____)"
#define ZEROS "00000000" /* hex 32 zero bits */
+#define FFFFS "ffffffff"

static int __init
plain_format(void)
@@ -243,6 +244,7 @@ plain_format(void)
#define PTR_STR "456789ab"
#define PTR_VAL_NO_CRNG "(ptrval)"
#define ZEROS ""
+#define FFFFS ""

static int __init
plain_format(void)
@@ -588,6 +590,17 @@ flags(void)
kfree(cmp_buffer);
}

+static void __init
+errptr(void)
+{
+ test("-1234", "%p", ERR_PTR(-1234));
+ test(FFFFS "ffffffff " FFFFS "ffffff00", "%px %px", ERR_PTR(-1), ERR_PTR(-256));
+#ifdef CONFIG_SYMBOLIC_ERRCODE
+ test("EIO EINVAL ENOSPC", "%p %p %p", ERR_PTR(-EIO), ERR_PTR(-EINVAL), ERR_PTR(-ENOSPC));
+ test("EAGAIN EAGAIN", "%p %p", ERR_PTR(-EAGAIN), ERR_PTR(-EWOULDBLOCK));
+#endif
+}
+
static void __init
test_pointer(void)
{
@@ -610,6 +623,7 @@ test_pointer(void)
bitmap();
netdev_features();
flags();
+ errptr();
}

static void __init selftest(void)
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index b0967cf17137..4b67fc23f3f2 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -21,6 +21,7 @@
#include <linux/build_bug.h>
#include <linux/clk.h>
#include <linux/clk-provider.h>
+#include <linux/errcode.h>
#include <linux/module.h> /* for KSYM_SYMBOL_LEN */
#include <linux/types.h>
#include <linux/string.h>
@@ -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);
+
+ /* If it's an ERR_PTR, try to print its symbolic representation. */
+ if (IS_ERR(ptr)) {
+ 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);
+ }
+
switch (*fmt) {
case 'F':
case 'f':
@@ -2178,8 +2204,6 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
return flags_string(buf, end, ptr, spec, fmt);
case 'O':
return kobject_string(buf, end, ptr, spec, fmt);
- case 'x':
- return pointer_string(buf, end, ptr, spec);
}

/* default is to _not_ leak addresses, hash before printing */
--
2.20.1
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