Add metal-pico library [v3]

This library hooks picolibc to libmetal, offering a small number of
APIs.

Signed-off-by: Keith Packard <keithp@keithp.com>

---

v2:

	Initialize TLS base register from __tls_base and __tdata_size

	    The RISC-V ABI sets the tp register between tls
	    initialized data and tls uninitialized data areas. The
	    linker sets __tls_base to the start of tls data and
	    __tdata_size to the size of the initialized data area, so
	    the correct tp value is the sum of these two symbols.

	libriscv__pico__metal.a → libmetal-pico.a

	    Use the name that freedom-e-sdk wants

	Use gloss/crt0.S and gloss/sys_exit.c for libmetal-pico.a

	    Share source code, especially the startup code, between
	    the two C library users to avoid duplicating work between
	    them.

	Expose sbrk/brk instead of _sbrk/_brk when compiled against picolibc

	    This changes the names of these two functions when using
	    picolibc instead of newlib. Otherwise, the implementation
	    is the same.

	Use gloss/sys_sbrk.c with picolibc

	    Instead of a separate copy with minor edits.

v3:
	Use correct TLS initialization value. Risc-V places TP
	at the base of TLS storage, not between data and BSS values.

Makefile.am

@@ -156,6 +156,20 @@ libmetal_a_SOURCES = \
 	src/vector.S \
 	src/watchdog.c
 
+########################################################
+# libmetal-pico
+########################################################
+
+lib_LIBRARIES += libmetail-pico.a
+
+libmetal_pico_a_SOURCES = \
+	gloss/crt0.S \
+	pico/iob.c \
+	gloss/sys_exit.c \
+	pico/times.c \
+	gloss/sys_sbrk.c \
+	pico/sysconf.c
+
 ########################################################
 # libgloss
 ########################################################

gloss/crt0.S

@@ -126,6 +126,10 @@ _start:
 #endif
 2:
 
+  /* Set TLS pointer */
+  .weak __tls_base	
+  la tp, __tls_base
+
   /* At this point we're in an environment that can execute C code.  The first
    * thing to do is to make the callback to the parent environment if it's been
    * requested to do so. */

gloss/sys_sbrk.c

@@ -8,26 +8,31 @@
  * that's been allocated. */
 extern char metal_segment_heap_target_start;
 extern char metal_segment_heap_target_end;
-static char *brk = &metal_segment_heap_target_start;
+static char *__brk = &metal_segment_heap_target_start;
+
+#ifdef _PICOLIBC__
+#define _brk brk
+#define _sbrk sbrk
+#endif
 
 int _brk(void *addr) {
-    brk = addr;
+    __brk = addr;
     return 0;
 }
 
 char *_sbrk(ptrdiff_t incr) {
-    char *old = brk;
+    char *old = __brk;
 
     /* If __heap_size == 0, we can't allocate memory on the heap */
     if (&metal_segment_heap_target_start == &metal_segment_heap_target_end) {
         return (void *)-1;
     }
 
     /* Don't move the break past the end of the heap */
-    if ((brk + incr) < &metal_segment_heap_target_end) {
-        brk += incr;
+    if ((__brk + incr) < &metal_segment_heap_target_end) {
+        __brk += incr;
     } else {
-        brk = &metal_segment_heap_target_end;
+        __brk = &metal_segment_heap_target_end;
         return (void *)-1;
     }
 

pico/iob.c

@@ -0,0 +1,44 @@
+/*
+ * Copyright © 2019 Keith Packard
+ *
+ * Permission to use, copy, modify, distribute, and sell this software and its
+ * documentation for any purpose is hereby granted without fee, provided that
+ * the above copyright notice appear in all copies and that both that copyright
+ * notice and this permission notice appear in supporting documentation, and
+ * that the name of the copyright holders not be used in advertising or
+ * publicity pertaining to distribution of the software without specific,
+ * written prior permission.  The copyright holders make no representations
+ * about the suitability of this software for any purpose.  It is provided "as
+ * is" without express or implied warranty.
+ *
+ * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+ * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
+ * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
+ * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
+ * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+ * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
+ * OF THIS SOFTWARE.
+ */
+
+#include <metal/tty.h>
+#include <stdio.h>
+
+static int metal_putc(char c, FILE *file) {
+    (void)file;
+    metal_tty_putc(c);
+    return c;
+}
+
+static int metal_getc(FILE *file) {
+    int c;
+    (void)file;
+    metal_tty_getc(&c);
+    return c;
+}
+
+static int metal_flush(FILE *file) { return 0; }
+
+static FILE __stdio =
+    FDEV_SETUP_STREAM(metal_putc, metal_getc, metal_flush, _FDEV_SETUP_RW);
+
+FILE *const __iob[3] = {&__stdio, &__stdio, &__stdio};

pico/sysconf.c

@@ -0,0 +1,16 @@
+#include <time.h>
+#include <unistd.h>
+
+/* Get configurable system variables.  */
+
+long sysconf(int name) {
+    unsigned long long timebase;
+
+    switch (name) {
+    case _SC_CLK_TCK:
+        metal_timer_get_timebase_frequency(0, &timebase);
+        return (long)timebase;
+    }
+
+    return -1;
+}

pico/times.c

@@ -0,0 +1,17 @@
+#include <metal/timer.h>
+#include <sys/time.h>
+#include <sys/times.h>
+
+/*
+ * Simple enough to return the tick count by
+ * just getting it from the hardware.
+ */
+
+clock_t times(struct tms *buf) {
+    unsigned long long mcc;
+    metal_timer_get_cyclecount(0, &mcc);
+    buf->tms_stime = 0;
+    buf->tms_cutime = 0;
+    buf->tms_cstime = 0;
+    return buf->tms_utime = mcc;
+}