[PATCH 4/4] ld.so: Add --list-tunables to print tunable values

["H.J. Lu" <hjl.tools@gmail.com>]

Pass --list-tunables to ld.so to print tunables with min and max values.
---
 NEWS                 |  2 ++
 elf/Makefile         |  8 ++++++++
 elf/dl-tunables.c    | 36 ++++++++++++++++++++++++++++++++++++
 elf/dl-tunables.h    |  2 ++
 elf/rtld.c           | 31 +++++++++++++++++++++++++++++--
 manual/tunables.texi | 37 +++++++++++++++++++++++++++++++++++++
 6 files changed, 114 insertions(+), 2 deletions(-)

diff --git a/NEWS b/NEWS
index fc8dd15439..f47516a02f 100644
--- a/NEWS
+++ b/NEWS
@@ -9,6 +9,8 @@ Version 2.33
 
 Major new features:
 
+* Pass --list-tunables to ld.so to print tunable values.
+
 * The mallinfo2 function is added to report statistics as per mallinfo,
   but with larger field widths to accurately report values that are
   larger than fit in an integer.
diff --git a/elf/Makefile b/elf/Makefile
index 0b78721848..11e90c9d17 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -44,6 +44,10 @@ dl-routines += dl-tunables
 tunables-type = $(addprefix TUNABLES_FRONTEND_,$(have-tunables))
 CPPFLAGS-dl-tunables.c += -DTUNABLES_FRONTEND=$(tunables-type)
 
+ifeq (yesyes,$(build-shared)$(run-built-tests))
+tests-special += $(objpfx)list-tunables.out
+endif
+
 # Make sure that the compiler does not insert any library calls in tunables
 # code paths.
 ifeq (yes,$(have-loop-to-function))
@@ -1796,3 +1800,7 @@ $(objpfx)tst-tls-ie-dlmopen.out: \
   $(objpfx)tst-tls-ie-mod6.so
 
 $(objpfx)tst-tls-surplus: $(libdl)
+
+$(objpfx)list-tunables.out: $(objpfx)ld.so
+	$(objpfx)ld.so --list-tunables > $@; \
+	$(evaluate-test)
diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
index b44174fe71..53226ef258 100644
--- a/elf/dl-tunables.c
+++ b/elf/dl-tunables.c
@@ -368,6 +368,42 @@ __tunables_init (char **envp)
     }
 }
 
+void
+__tunables_print (void)
+{
+  for (int i = 0; i < sizeof (tunable_list) / sizeof (tunable_t); i++)
+    {
+      tunable_t *cur = &tunable_list[i];
+      _dl_printf ("%s: ", cur->name);
+      switch (cur->type.type_code)
+	{
+	case TUNABLE_TYPE_INT_32:
+	  _dl_printf ("%d (min: %d, max: %d)\n",
+		      (int) cur->val.numval,
+		      (int) cur->type.min,
+		      (int) cur->type.max);
+	  break;
+	case TUNABLE_TYPE_UINT_64:
+	  _dl_printf ("0x%lx (min: 0x%lx, max: 0x%lx)\n",
+		      (long int) cur->val.numval,
+		      (long int) cur->type.min,
+		      (long int) cur->type.max);
+	  break;
+	case TUNABLE_TYPE_SIZE_T:
+	  _dl_printf ("0x%Zx (min: 0x%Zx, max: 0x%Zx)\n",
+		      (size_t) cur->val.numval,
+		      (size_t) cur->type.min,
+		      (size_t) cur->type.max);
+	  break;
+	case TUNABLE_TYPE_STRING:
+	  _dl_printf ("%s\n", cur->val.strval ? cur->val.strval : "");
+	  break;
+	default:
+	  __builtin_unreachable ();
+	}
+    }
+}
+
 /* Set the tunable value.  This is called by the module that the tunable exists
    in. */
 void
diff --git a/elf/dl-tunables.h b/elf/dl-tunables.h
index b1add3184f..a2c728f0dd 100644
--- a/elf/dl-tunables.h
+++ b/elf/dl-tunables.h
@@ -69,9 +69,11 @@ typedef struct _tunable tunable_t;
 # include "dl-tunable-list.h"
 
 extern void __tunables_init (char **);
+extern void __tunables_print (void);
 extern void __tunable_get_val (tunable_id_t, void *, tunable_callback_t);
 extern void __tunable_set_val (tunable_id_t, void *, void *, void *);
 rtld_hidden_proto (__tunables_init)
+rtld_hidden_proto (__tunables_print)
 rtld_hidden_proto (__tunable_get_val)
 rtld_hidden_proto (__tunable_set_val)
 
diff --git a/elf/rtld.c b/elf/rtld.c
index 5b882163fa..f76b9b0265 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -48,6 +48,10 @@
 #include <array_length.h>
 #include <libc-early-init.h>
 
+#if HAVE_TUNABLES
+# include <dl-tunables.h>
+#endif
+
 #include <assert.h>
 
 /* Only enables rtld profiling for architectures which provides non generic
@@ -168,7 +172,7 @@ static void audit_list_add_dynamic_tag (struct audit_list *,
 static const char *audit_list_next (struct audit_list *);
 
 /* This is a list of all the modes the dynamic loader can be in.  */
-enum mode { normal, list, verify, trace };
+enum mode { normal, list, verify, trace, list_tunables };
 
 /* Process all environments variables the dynamic linker must recognize.
    Since all of them start with `LD_' we are a bit smarter while finding
@@ -1263,9 +1267,27 @@ dl_main (const ElfW(Phdr) *phdr,
 	    _dl_argc -= 2;
 	    _dl_argv += 2;
 	  }
+#if HAVE_TUNABLES
+	else if (! strcmp (_dl_argv[1], "--list-tunables"))
+	  {
+	    mode = list_tunables;
+
+	    ++_dl_skip_args;
+	    --_dl_argc;
+	    ++_dl_argv;
+	  }
+#endif
 	else
 	  break;
 
+#if HAVE_TUNABLES
+      if (__builtin_expect (mode, normal) == list_tunables)
+	{
+	  __tunables_print ();
+	  _exit (0);
+	}
+#endif
+
       /* If we have no further argument the program was called incorrectly.
 	 Grant the user some education.  */
       if (_dl_argc < 2)
@@ -1292,7 +1314,12 @@ of this helper program; chances are you did not intend to run this program.\n\
   --inhibit-rpath LIST  ignore RUNPATH and RPATH information in object names\n\
 			in LIST\n\
   --audit LIST          use objects named in LIST as auditors\n\
-  --preload LIST        preload objects named in LIST\n");
+  --preload LIST        preload objects named in LIST\n"
+#if HAVE_TUNABLES
+"\
+  --list-tunables       list all tunables with minimum and maximum values\n"
+#endif
+	  );
 
       ++_dl_skip_args;
       --_dl_argc;
diff --git a/manual/tunables.texi b/manual/tunables.texi
index 23ef0d40e7..38c8578229 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -28,6 +28,43 @@ Finally, the set of tunables available may vary between distributions as
 the tunables feature allows distributions to add their own tunables under
 their own namespace.
 
+Passing @option{--list-tunables} to the dynamic loader to print all
+tunables with minimum and maximum values:
+
+@example
+$ /lib64/ld-linux-x86-64.so.2 --list-tunables
+glibc.rtld.nns: 0x4 (min: 0x1, max: 0x10)
+glibc.elision.skip_lock_after_retries: 3 (min: -2147483648, max: 2147483647)
+glibc.malloc.trim_threshold: 0x0 (min: 0x0, max: 0xffffffffffffffff)
+glibc.malloc.perturb: 0 (min: 0, max: 255)
+glibc.cpu.x86_shared_cache_size: 0x100000 (min: 0x0, max: 0xffffffffffffffff)
+glibc.elision.tries: 3 (min: -2147483648, max: 2147483647)
+glibc.elision.enable: 0 (min: 0, max: 1)
+glibc.cpu.x86_rep_movsb_threshold: 0x800 (min: 0x100, max: 0xffffffffffffffff)
+glibc.malloc.mxfast: 0x0 (min: 0x0, max: 0xffffffffffffffff)
+glibc.elision.skip_lock_busy: 3 (min: -2147483648, max: 2147483647)
+glibc.malloc.top_pad: 0x0 (min: 0x0, max: 0xffffffffffffffff)
+glibc.cpu.x86_rep_stosb_threshold: 0x800 (min: 0x1, max: 0xffffffffffffffff)
+glibc.cpu.x86_non_temporal_threshold: 0x600000 (min: 0x0, max: 0xffffffffffffffff)
+glibc.cpu.x86_shstk: 
+glibc.cpu.hwcap_mask: 0x6 (min: 0x0, max: 0xffffffffffffffff)
+glibc.malloc.mmap_max: 0 (min: -2147483648, max: 2147483647)
+glibc.elision.skip_trylock_internal_abort: 3 (min: -2147483648, max: 2147483647)
+glibc.malloc.tcache_unsorted_limit: 0x0 (min: 0x0, max: 0xffffffffffffffff)
+glibc.cpu.x86_ibt: 
+glibc.cpu.hwcaps: 
+glibc.elision.skip_lock_internal_abort: 3 (min: -2147483648, max: 2147483647)
+glibc.malloc.arena_max: 0x0 (min: 0x1, max: 0xffffffffffffffff)
+glibc.malloc.mmap_threshold: 0x0 (min: 0x0, max: 0xffffffffffffffff)
+glibc.cpu.x86_data_cache_size: 0x8000 (min: 0x0, max: 0xffffffffffffffff)
+glibc.malloc.tcache_count: 0x0 (min: 0x0, max: 0xffffffffffffffff)
+glibc.malloc.arena_test: 0x0 (min: 0x1, max: 0xffffffffffffffff)
+glibc.pthread.mutex_spin_count: 100 (min: 0, max: 32767)
+glibc.rtld.optional_static_tls: 0x200 (min: 0x0, max: 0xffffffffffffffff)
+glibc.malloc.tcache_max: 0x0 (min: 0x0, max: 0xffffffffffffffff)
+glibc.malloc.check: 0 (min: 0, max: 3)
+@end example
+
 @menu
 * Tunable names::  The structure of a tunable name
 * Memory Allocation Tunables::  Tunables in the memory allocation subsystem
-- 
2.26.2