diff --git a/lang/cem/libcc.ansi/build.lua b/lang/cem/libcc.ansi/build.lua
index c49bdf0e2..b40ec30ec 100644
--- a/lang/cem/libcc.ansi/build.lua
+++ b/lang/cem/libcc.ansi/build.lua
@@ -2,12 +2,12 @@ include("plat/build.lua")
 
 tabgen {
 	name = "ctype_tab",
-	srcs = { "./pure/ctype/char.tab" }
+	srcs = { "./core/ctype/char.tab" }
 }
 
 normalrule {
 	name = "ctype_files",
-	ins = { "./pure/ctype/genfiles" },
+	ins = { "./core/ctype/genfiles" },
 	outleaves = {
 		"isalnum.c",
 		"isalpha.c",
@@ -33,14 +33,14 @@ for _, plat in ipairs(vars.plats) do
 		srcs = {
 			"+ctype_files",
 			"+ctype_tab",
-			"./pure/string/*.c",
-			"./pure/stdlib/*.c",
-			"./pure/locale/*.c",
-			"./pure/setjmp/*.c",
-			"./pure/setjmp/*.e",
-			"./pure/math/*.c", -- hypot.c
-			"./pure/math/*.e",
-			"./pure/ctype/*.c",
+			"./core/string/*.c",
+			"./core/stdlib/*.c",
+			"./core/locale/*.c",
+			"./core/setjmp/*.c",
+			"./core/setjmp/*.e",
+			"./core/math/*.c", -- hypot.c
+			"./core/math/*.e",
+			"./core/ctype/*.c",
 			"./errno/*.c",
 			"./malloc/*.c",
 			"./misc/environ.c", -- don't build everything here as it's all obsolete
@@ -56,7 +56,7 @@ for _, plat in ipairs(vars.plats) do
 			"lang/cem/libcc.ansi/headers+pkg",
 			"plat/"..plat.."/include+pkg",
 			"./malloc/malloc.h",
-			"./pure/math/localmath.h",
+			"./core/math/localmath.h",
 			"./stdio/loc_incl.h",
 			"./stdlib/ext_fmt.h",
 			"./time/loc_time.h",
diff --git a/lang/cem/libcc.ansi/core/README.md b/lang/cem/libcc.ansi/core/README.md
new file mode 100644
index 000000000..48243c8c6
--- /dev/null
+++ b/lang/cem/libcc.ansi/core/README.md
@@ -0,0 +1,19 @@
+This directory contains the libc core: functions here may depend on other
+libc functions _only_ (so, no `unistd.h` stuff). Plats don't get to configure
+this, so nothing here should add any overhead if the function isn't linked.
+
+Examples of what goes here:
+
+  - `strcmp()` --- because it's pure code.
+  - `setjmp()` --- in EM, it's portable.
+  - `assert()` --- because it only calls other core functions (`fputs()`
+    and `abort()`).
+
+Examples of what doesn't go here:
+
+  - `malloc()` --- because it calls the `unistd.h` function `sbrk()` (and so a
+    plat might want to swap it out).
+  - stdio --- because it calls the `unistd.h` functions `read()`, `write()`
+    etc.
+  - `signal()` --- because it can't be implemented portably and needs to go
+    in the plat.
diff --git a/lang/cem/libcc.ansi/pure/ctype/char.tab b/lang/cem/libcc.ansi/core/ctype/char.tab
similarity index 100%
rename from lang/cem/libcc.ansi/pure/ctype/char.tab
rename to lang/cem/libcc.ansi/core/ctype/char.tab
diff --git a/lang/cem/libcc.ansi/pure/ctype/genfiles b/lang/cem/libcc.ansi/core/ctype/genfiles
similarity index 100%
rename from lang/cem/libcc.ansi/pure/ctype/genfiles
rename to lang/cem/libcc.ansi/core/ctype/genfiles
diff --git a/lang/cem/libcc.ansi/pure/ctype/tolower.c b/lang/cem/libcc.ansi/core/ctype/tolower.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/ctype/tolower.c
rename to lang/cem/libcc.ansi/core/ctype/tolower.c
diff --git a/lang/cem/libcc.ansi/pure/ctype/toupper.c b/lang/cem/libcc.ansi/core/ctype/toupper.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/ctype/toupper.c
rename to lang/cem/libcc.ansi/core/ctype/toupper.c
diff --git a/lang/cem/libcc.ansi/pure/locale/localeconv.c b/lang/cem/libcc.ansi/core/locale/localeconv.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/locale/localeconv.c
rename to lang/cem/libcc.ansi/core/locale/localeconv.c
diff --git a/lang/cem/libcc.ansi/pure/locale/setlocale.c b/lang/cem/libcc.ansi/core/locale/setlocale.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/locale/setlocale.c
rename to lang/cem/libcc.ansi/core/locale/setlocale.c
diff --git a/lang/cem/libcc.ansi/pure/math/asin.c b/lang/cem/libcc.ansi/core/math/asin.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/asin.c
rename to lang/cem/libcc.ansi/core/math/asin.c
diff --git a/lang/cem/libcc.ansi/pure/math/atan.c b/lang/cem/libcc.ansi/core/math/atan.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/atan.c
rename to lang/cem/libcc.ansi/core/math/atan.c
diff --git a/lang/cem/libcc.ansi/pure/math/atan2.c b/lang/cem/libcc.ansi/core/math/atan2.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/atan2.c
rename to lang/cem/libcc.ansi/core/math/atan2.c
diff --git a/lang/cem/libcc.ansi/pure/math/ceil.c b/lang/cem/libcc.ansi/core/math/ceil.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/ceil.c
rename to lang/cem/libcc.ansi/core/math/ceil.c
diff --git a/lang/cem/libcc.ansi/pure/math/exp.c b/lang/cem/libcc.ansi/core/math/exp.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/exp.c
rename to lang/cem/libcc.ansi/core/math/exp.c
diff --git a/lang/cem/libcc.ansi/pure/math/fabs.c b/lang/cem/libcc.ansi/core/math/fabs.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/fabs.c
rename to lang/cem/libcc.ansi/core/math/fabs.c
diff --git a/lang/cem/libcc.ansi/pure/math/floor.c b/lang/cem/libcc.ansi/core/math/floor.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/floor.c
rename to lang/cem/libcc.ansi/core/math/floor.c
diff --git a/lang/cem/libcc.ansi/pure/math/fmod.c b/lang/cem/libcc.ansi/core/math/fmod.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/fmod.c
rename to lang/cem/libcc.ansi/core/math/fmod.c
diff --git a/lang/cem/libcc.ansi/pure/math/frexp.e b/lang/cem/libcc.ansi/core/math/frexp.e
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/frexp.e
rename to lang/cem/libcc.ansi/core/math/frexp.e
diff --git a/lang/cem/libcc.ansi/pure/math/hugeval.c b/lang/cem/libcc.ansi/core/math/hugeval.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/hugeval.c
rename to lang/cem/libcc.ansi/core/math/hugeval.c
diff --git a/lang/cem/libcc.ansi/pure/math/hypot.c b/lang/cem/libcc.ansi/core/math/hypot.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/hypot.c
rename to lang/cem/libcc.ansi/core/math/hypot.c
diff --git a/lang/cem/libcc.ansi/pure/math/isnan.c b/lang/cem/libcc.ansi/core/math/isnan.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/isnan.c
rename to lang/cem/libcc.ansi/core/math/isnan.c
diff --git a/lang/cem/libcc.ansi/pure/math/ldexp.c b/lang/cem/libcc.ansi/core/math/ldexp.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/ldexp.c
rename to lang/cem/libcc.ansi/core/math/ldexp.c
diff --git a/lang/cem/libcc.ansi/pure/math/localmath.h b/lang/cem/libcc.ansi/core/math/localmath.h
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/localmath.h
rename to lang/cem/libcc.ansi/core/math/localmath.h
diff --git a/lang/cem/libcc.ansi/pure/math/log.c b/lang/cem/libcc.ansi/core/math/log.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/log.c
rename to lang/cem/libcc.ansi/core/math/log.c
diff --git a/lang/cem/libcc.ansi/pure/math/log10.c b/lang/cem/libcc.ansi/core/math/log10.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/log10.c
rename to lang/cem/libcc.ansi/core/math/log10.c
diff --git a/lang/cem/libcc.ansi/pure/math/modf.e b/lang/cem/libcc.ansi/core/math/modf.e
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/modf.e
rename to lang/cem/libcc.ansi/core/math/modf.e
diff --git a/lang/cem/libcc.ansi/pure/math/pow.c b/lang/cem/libcc.ansi/core/math/pow.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/pow.c
rename to lang/cem/libcc.ansi/core/math/pow.c
diff --git a/lang/cem/libcc.ansi/pure/math/sin.c b/lang/cem/libcc.ansi/core/math/sin.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/sin.c
rename to lang/cem/libcc.ansi/core/math/sin.c
diff --git a/lang/cem/libcc.ansi/pure/math/sinh.c b/lang/cem/libcc.ansi/core/math/sinh.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/sinh.c
rename to lang/cem/libcc.ansi/core/math/sinh.c
diff --git a/lang/cem/libcc.ansi/pure/math/sqrt.c b/lang/cem/libcc.ansi/core/math/sqrt.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/sqrt.c
rename to lang/cem/libcc.ansi/core/math/sqrt.c
diff --git a/lang/cem/libcc.ansi/pure/math/tan.c b/lang/cem/libcc.ansi/core/math/tan.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/tan.c
rename to lang/cem/libcc.ansi/core/math/tan.c
diff --git a/lang/cem/libcc.ansi/pure/math/tanh.c b/lang/cem/libcc.ansi/core/math/tanh.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/math/tanh.c
rename to lang/cem/libcc.ansi/core/math/tanh.c
diff --git a/lang/cem/libcc.ansi/pure/setjmp/setjmp.e b/lang/cem/libcc.ansi/core/setjmp/setjmp.e
similarity index 100%
rename from lang/cem/libcc.ansi/pure/setjmp/setjmp.e
rename to lang/cem/libcc.ansi/core/setjmp/setjmp.e
diff --git a/lang/cem/libcc.ansi/pure/setjmp/sigmisc.c b/lang/cem/libcc.ansi/core/setjmp/sigmisc.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/setjmp/sigmisc.c
rename to lang/cem/libcc.ansi/core/setjmp/sigmisc.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/abs.c b/lang/cem/libcc.ansi/core/stdlib/abs.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/abs.c
rename to lang/cem/libcc.ansi/core/stdlib/abs.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/atoi.c b/lang/cem/libcc.ansi/core/stdlib/atoi.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/atoi.c
rename to lang/cem/libcc.ansi/core/stdlib/atoi.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/atol.c b/lang/cem/libcc.ansi/core/stdlib/atol.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/atol.c
rename to lang/cem/libcc.ansi/core/stdlib/atol.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/bsearch.c b/lang/cem/libcc.ansi/core/stdlib/bsearch.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/bsearch.c
rename to lang/cem/libcc.ansi/core/stdlib/bsearch.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/div.c b/lang/cem/libcc.ansi/core/stdlib/div.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/div.c
rename to lang/cem/libcc.ansi/core/stdlib/div.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/getenv.c b/lang/cem/libcc.ansi/core/stdlib/getenv.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/getenv.c
rename to lang/cem/libcc.ansi/core/stdlib/getenv.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/labs.c b/lang/cem/libcc.ansi/core/stdlib/labs.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/labs.c
rename to lang/cem/libcc.ansi/core/stdlib/labs.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/ldiv.c b/lang/cem/libcc.ansi/core/stdlib/ldiv.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/ldiv.c
rename to lang/cem/libcc.ansi/core/stdlib/ldiv.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/mblen.c b/lang/cem/libcc.ansi/core/stdlib/mblen.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/mblen.c
rename to lang/cem/libcc.ansi/core/stdlib/mblen.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/mbstowcs.c b/lang/cem/libcc.ansi/core/stdlib/mbstowcs.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/mbstowcs.c
rename to lang/cem/libcc.ansi/core/stdlib/mbstowcs.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/mbtowc.c b/lang/cem/libcc.ansi/core/stdlib/mbtowc.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/mbtowc.c
rename to lang/cem/libcc.ansi/core/stdlib/mbtowc.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/putenv.c b/lang/cem/libcc.ansi/core/stdlib/putenv.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/putenv.c
rename to lang/cem/libcc.ansi/core/stdlib/putenv.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/qsort.c b/lang/cem/libcc.ansi/core/stdlib/qsort.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/qsort.c
rename to lang/cem/libcc.ansi/core/stdlib/qsort.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/rand.c b/lang/cem/libcc.ansi/core/stdlib/rand.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/rand.c
rename to lang/cem/libcc.ansi/core/stdlib/rand.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/setenv.c b/lang/cem/libcc.ansi/core/stdlib/setenv.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/setenv.c
rename to lang/cem/libcc.ansi/core/stdlib/setenv.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/strtol.c b/lang/cem/libcc.ansi/core/stdlib/strtol.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/strtol.c
rename to lang/cem/libcc.ansi/core/stdlib/strtol.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/wcstombs.c b/lang/cem/libcc.ansi/core/stdlib/wcstombs.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/wcstombs.c
rename to lang/cem/libcc.ansi/core/stdlib/wcstombs.c
diff --git a/lang/cem/libcc.ansi/pure/stdlib/wctomb.c b/lang/cem/libcc.ansi/core/stdlib/wctomb.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/stdlib/wctomb.c
rename to lang/cem/libcc.ansi/core/stdlib/wctomb.c
diff --git a/lang/cem/libcc.ansi/pure/string/memchr.c b/lang/cem/libcc.ansi/core/string/memchr.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/memchr.c
rename to lang/cem/libcc.ansi/core/string/memchr.c
diff --git a/lang/cem/libcc.ansi/pure/string/memcmp.c b/lang/cem/libcc.ansi/core/string/memcmp.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/memcmp.c
rename to lang/cem/libcc.ansi/core/string/memcmp.c
diff --git a/lang/cem/libcc.ansi/pure/string/memcpy.c b/lang/cem/libcc.ansi/core/string/memcpy.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/memcpy.c
rename to lang/cem/libcc.ansi/core/string/memcpy.c
diff --git a/lang/cem/libcc.ansi/pure/string/memmove.c b/lang/cem/libcc.ansi/core/string/memmove.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/memmove.c
rename to lang/cem/libcc.ansi/core/string/memmove.c
diff --git a/lang/cem/libcc.ansi/pure/string/memset.c b/lang/cem/libcc.ansi/core/string/memset.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/memset.c
rename to lang/cem/libcc.ansi/core/string/memset.c
diff --git a/lang/cem/libcc.ansi/pure/string/strcat.c b/lang/cem/libcc.ansi/core/string/strcat.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strcat.c
rename to lang/cem/libcc.ansi/core/string/strcat.c
diff --git a/lang/cem/libcc.ansi/pure/string/strchr.c b/lang/cem/libcc.ansi/core/string/strchr.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strchr.c
rename to lang/cem/libcc.ansi/core/string/strchr.c
diff --git a/lang/cem/libcc.ansi/pure/string/strcmp.c b/lang/cem/libcc.ansi/core/string/strcmp.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strcmp.c
rename to lang/cem/libcc.ansi/core/string/strcmp.c
diff --git a/lang/cem/libcc.ansi/pure/string/strcoll.c b/lang/cem/libcc.ansi/core/string/strcoll.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strcoll.c
rename to lang/cem/libcc.ansi/core/string/strcoll.c
diff --git a/lang/cem/libcc.ansi/pure/string/strcpy.c b/lang/cem/libcc.ansi/core/string/strcpy.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strcpy.c
rename to lang/cem/libcc.ansi/core/string/strcpy.c
diff --git a/lang/cem/libcc.ansi/pure/string/strcspn.c b/lang/cem/libcc.ansi/core/string/strcspn.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strcspn.c
rename to lang/cem/libcc.ansi/core/string/strcspn.c
diff --git a/lang/cem/libcc.ansi/pure/string/strdup.c b/lang/cem/libcc.ansi/core/string/strdup.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strdup.c
rename to lang/cem/libcc.ansi/core/string/strdup.c
diff --git a/lang/cem/libcc.ansi/pure/string/strlen.c b/lang/cem/libcc.ansi/core/string/strlen.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strlen.c
rename to lang/cem/libcc.ansi/core/string/strlen.c
diff --git a/lang/cem/libcc.ansi/pure/string/strncat.c b/lang/cem/libcc.ansi/core/string/strncat.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strncat.c
rename to lang/cem/libcc.ansi/core/string/strncat.c
diff --git a/lang/cem/libcc.ansi/pure/string/strncmp.c b/lang/cem/libcc.ansi/core/string/strncmp.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strncmp.c
rename to lang/cem/libcc.ansi/core/string/strncmp.c
diff --git a/lang/cem/libcc.ansi/pure/string/strncpy.c b/lang/cem/libcc.ansi/core/string/strncpy.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strncpy.c
rename to lang/cem/libcc.ansi/core/string/strncpy.c
diff --git a/lang/cem/libcc.ansi/pure/string/strpbrk.c b/lang/cem/libcc.ansi/core/string/strpbrk.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strpbrk.c
rename to lang/cem/libcc.ansi/core/string/strpbrk.c
diff --git a/lang/cem/libcc.ansi/pure/string/strrchr.c b/lang/cem/libcc.ansi/core/string/strrchr.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strrchr.c
rename to lang/cem/libcc.ansi/core/string/strrchr.c
diff --git a/lang/cem/libcc.ansi/pure/string/strspn.c b/lang/cem/libcc.ansi/core/string/strspn.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strspn.c
rename to lang/cem/libcc.ansi/core/string/strspn.c
diff --git a/lang/cem/libcc.ansi/pure/string/strstr.c b/lang/cem/libcc.ansi/core/string/strstr.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strstr.c
rename to lang/cem/libcc.ansi/core/string/strstr.c
diff --git a/lang/cem/libcc.ansi/pure/string/strtok.c b/lang/cem/libcc.ansi/core/string/strtok.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strtok.c
rename to lang/cem/libcc.ansi/core/string/strtok.c
diff --git a/lang/cem/libcc.ansi/pure/string/strxfrm.c b/lang/cem/libcc.ansi/core/string/strxfrm.c
similarity index 100%
rename from lang/cem/libcc.ansi/pure/string/strxfrm.c
rename to lang/cem/libcc.ansi/core/string/strxfrm.c
diff --git a/lang/cem/libcc.ansi/pure/README.md b/lang/cem/libcc.ansi/pure/README.md
deleted file mode 100644
index 484205837..000000000
--- a/lang/cem/libcc.ansi/pure/README.md
+++ /dev/null
@@ -1,3 +0,0 @@
-This directory contains _only_ pure-code libc functions with no dependencies
-on anything other than other pure functions (for example: strcmp, div). There
-should be no reason why any platform won't want these in its libc.