feat(esp_libc): add full support for picolibc

components/esp_system/ld/esp32c2/sections.ld.in

@@ -188,6 +188,9 @@ SECTIONS
 
     mapping[flash_rodata]
 
+#if CONFIG_LIBC_PICOLIBC
+    *(.got .got.plt) /* TODO: GCC-439 */
+#endif
     *(.irom1.text) /* catch stray ICACHE_RODATA_ATTR */
     *(.gnu.linkonce.r.*)
     *(.rodata1)
@@ -262,24 +265,41 @@ SECTIONS
 
   .flash.tdata :
   {
+    /* Keep tdata and tbss sections contiguous (no gaps between them).
+     * The TLS runtime code calculates offsets assuming these sections are
+     * adjacent. Gaps would cause incorrect address calculations, leading
+     * to accessing wrong memory.
+     */
+    /* tdata sections */
     _thread_local_data_start = ABSOLUTE(.);
-
+#if CONFIG_LIBC_PICOLIBC
+    _picolibc_reent_stub_start = ABSOLUTE(.);
+    KEEP(*(.tdata.errno))
+#if CONFIG_LIBC_PICOLIBC_NEWLIB_COMPATIBILITY
+    /* Reproduce the public fields from struct _reent. */
+    KEEP(*(.tdata.tls_stdin))
+    KEEP(*(.tdata.tls_stdout))
+    KEEP(*(.tdata.tls_stderr))
+#endif // CONFIG_LIBC_PICOLIBC_NEWLIB_COMPATIBILITY
+    _picolibc_reent_stub_end = ABSOLUTE(.);
+#endif // CONFIG_LIBC_PICOLIBC
     *(.tdata .tdata.* .gnu.linkonce.td.*)
-
     . = ALIGN(ALIGNOF(.flash.tbss));
     _thread_local_data_end = ABSOLUTE(.);
   } > default_rodata_seg
   ASSERT_SECTIONS_GAP(.flash.tdata, .flash.tbss)
+  ASSERT_PICOLIBC_REENT_STUB()
 
   .flash.tbss (NOLOAD) :
   {
+    /* tbss sections */
     _thread_local_bss_start = ABSOLUTE(.);
-
     *(.tbss .tbss.* .gnu.linkonce.tb.*)
     *(.tcommon .tcommon.*)
-
     _thread_local_bss_end = ABSOLUTE(.);
   } > default_rodata_seg
+  ASSERT(_thread_local_data_end == _thread_local_bss_start,
+         "tdata and tbss must be contiguous.")
 
   /**
    * This section contains all the rodata that is not used
@@ -292,7 +312,7 @@ SECTIONS
      * driver to maintain the virtual address.
      * NOLOAD rodata may not be included in this section.
      */
-    _rodata_reserved_end = ADDR(.flash.tbss);
+    _rodata_reserved_end = .;
 
     mapping[rodata_noload]
   } > default_rodata_seg