libbb: optionally honour libc provided SIGRTMIN/SIGRTMAX in get_signum()

When an application documents that it responds such and such to
SIGRTMIN+n, that almost always means with respect to the libc-provided
SIGRTMIN. Hence I disagree with the "more correct" in commit
7b276fc17594. In any case, this is rather unfortunate:

36
34

(the first shell is bash). We probably can't change default behaviour
after 7 years, but at least we can provide a config option.

We avoid a little code generation (repeated calls to
__libc_current_sigrtmin) by stashing SIGRTMIN/SIGRTMAX in local
variables, but it does cost ~50 bytes. The next patch serves as penance
for that.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/libbb/u_signal_names.c b/libbb/u_signal_names.c
index b3038e32ddd0c8219c42c2edf2a899e6c9faf6f5..866ca85fda9e19ad1bdd2a3a7e3e80e994373f5c 100644 (file)
--- a/libbb/u_signal_names.c
+++ b/libbb/u_signal_names.c
@@ -12,6 +12,18 @@
 //config:      help
 //config:      Support RTMIN[+n] and RTMAX[-n] signal names
 //config:      in kill, killall etc. This costs ~250 bytes.
+//config:
+//config:config FEATURE_RTMINMAX_USE_LIBC_DEFINITIONS
+//config:      bool "Use the definitions of SIGRTMIN/SIGRTMAX provided by libc"
+//config:      default y
+//config:      depends on FEATURE_RTMINMAX
+//config:      help
+//config:      Some C libraries reserve a few real-time signals for internal
+//config:      use, and adjust the values of SIGRTMIN/SIGRTMAX seen by
+//config:      applications accordingly. Saying yes here means that a signal
+//config:      name RTMIN+n will be interpreted according to the libc definition
+//config:      of SIGRTMIN, and not the raw definition provided by the kernel.
+//config:      This behavior matches "kill -l RTMIN+n" from bash.
 
 #include "libbb.h"
 
@@ -123,7 +135,7 @@ static const char signals[][7] ALIGN1 = {
 #ifdef SIGSYS
        [SIGSYS   ] = "SYS",
 #endif
-#if ENABLE_FEATURE_RTMINMAX
+#if ENABLE_FEATURE_RTMINMAX && !ENABLE_FEATURE_RTMINMAX_USE_LIBC_DEFINITIONS
 # ifdef __SIGRTMIN
        [__SIGRTMIN] = "RTMIN",
 # endif
@@ -168,36 +180,46 @@ int FAST_FUNC get_signum(const char *name)
 # endif
 #endif
 
-#if ENABLE_FEATURE_RTMINMAX
-# if defined(SIGRTMIN) && defined(SIGRTMAX)
-/* libc may use some rt sigs for pthreads and therefore "remap" SIGRTMIN/MAX,
- * but we want to use "raw" SIGRTMIN/MAX. Underscored names, if exist, provide
- * them. If they don't exist, fall back to non-underscored ones: */
+#if ENABLE_FEATURE_RTMINMAX && defined(SIGRTMIN) && defined(SIGRTMAX)
+       {
+# if ENABLE_FEATURE_RTMINMAX_USE_LIBC_DEFINITIONS
+               /* Use the libc provided values. */
+               unsigned sigrtmin = SIGRTMIN;
+               unsigned sigrtmax = SIGRTMAX;
+# else
+       /* Use the "raw" SIGRTMIN/MAX. Underscored names, if exist, provide
+        * them. If they don't exist, fall back to non-underscored ones: */
 #  if !defined(__SIGRTMIN)
 #   define __SIGRTMIN SIGRTMIN
 #  endif
 #  if !defined(__SIGRTMAX)
 #   define __SIGRTMAX SIGRTMAX
 #  endif
-       if (strncasecmp(name, "RTMIN", 5) == 0) {
-               if (!name[5])
-                       return __SIGRTMIN;
-               if (name[5] == '+') {
-                       i = bb_strtou(name + 6, NULL, 10);
-                       if (!errno && i <= __SIGRTMAX - __SIGRTMIN)
-                               return __SIGRTMIN + i;
+
+#  define sigrtmin __SIGRTMIN
+#  define sigrtmax __SIGRTMAX
+# endif
+               if (strncasecmp(name, "RTMIN", 5) == 0) {
+                       if (!name[5])
+                               return sigrtmin;
+                       if (name[5] == '+') {
+                               i = bb_strtou(name + 6, NULL, 10);
+                               if (!errno && i <= sigrtmax - sigrtmin)
+                                       return sigrtmin + i;
+                       }
                }
-       }
-       else if (strncasecmp(name, "RTMAX", 5) == 0) {
-               if (!name[5])
-                       return __SIGRTMAX;
-               if (name[5] == '-') {
-                       i = bb_strtou(name + 6, NULL, 10);
-                       if (!errno && i <= __SIGRTMAX - __SIGRTMIN)
-                               return __SIGRTMAX - i;
+               else if (strncasecmp(name, "RTMAX", 5) == 0) {
+                       if (!name[5])
+                               return sigrtmax;
+                       if (name[5] == '-') {
+                               i = bb_strtou(name + 6, NULL, 10);
+                               if (!errno && i <= sigrtmax - sigrtmin)
+                                       return sigrtmax - i;
+                       }
                }
+# undef sigrtmin
+# undef sigrtmax
        }
-# endif
 #endif
 
        return -1;
@@ -228,8 +250,16 @@ void FAST_FUNC print_signames(void)
                        printf("%2u) %s\n", signo, name);
        }
 #if ENABLE_FEATURE_RTMINMAX
-# ifdef __SIGRTMAX
+# if ENABLE_FEATURE_RTMINMAX_USE_LIBC_DEFINITIONS
+#  if defined(SIGRTMIN) && defined(SIGRTMAX)
+       printf("%2u) %s\n", SIGRTMIN, "RTMIN");
+       printf("%2u) %s\n", SIGRTMAX, "RTMAX");
+#  endif
+# else
+// __SIGRTMIN is included in signals[] array.
+#  ifdef __SIGRTMAX
        printf("%2u) %s\n", __SIGRTMAX, "RTMAX");
+#  endif
 # endif
 #endif
 }