Move C++ vtables into IRAM, out of HEAP (#4179)

GCC places vtables in .rodata, with a mangled name of "_ZTV*."  Because
these are simply address jump tables, there is no need to place them in
RAM.  Instead, have the linker place them in the .text (aka IRAM) section.
This will free up a variable amount of heap space, depending on the number
of classes with virtual functions used in any particular project.

Author: earlephilhower

tools/sdk/ld/eagle.app.v6.common.ld

@@ -84,72 +84,6 @@ SECTIONS
     _data_end = ABSOLUTE(.);
   } >dram0_0_seg :dram0_0_phdr
 
-  .rodata : ALIGN(4)
-  {
-    _rodata_start = ABSOLUTE(.);
-    *(.sdk.version)
-    *(.rodata)
-    *(.rodata.*)
-    *(.gnu.linkonce.r.*)
-    *(.rodata1)
-    __XT_EXCEPTION_TABLE__ = ABSOLUTE(.);
-    *(.xt_except_table)
-    *(.gcc_except_table)
-    *(.gnu.linkonce.e.*)
-    *(.gnu.version_r)
-    *(.eh_frame)
-    . = (. + 3) & ~ 3;
-    /*  C++ constructor and destructor tables, properly ordered:  */
-    __init_array_start = ABSOLUTE(.);
-    KEEP (*crtbegin.o(.ctors))
-    KEEP (*(EXCLUDE_FILE (*crtend.o) .ctors))
-    KEEP (*(SORT(.ctors.*)))
-    KEEP (*(.ctors))
-    __init_array_end = ABSOLUTE(.);
-    KEEP (*crtbegin.o(.dtors))
-    KEEP (*(EXCLUDE_FILE (*crtend.o) .dtors))
-    KEEP (*(SORT(.dtors.*)))
-    KEEP (*(.dtors))
-    /*  C++ exception handlers table:  */
-    __XT_EXCEPTION_DESCS__ = ABSOLUTE(.);
-    *(.xt_except_desc)
-    *(.gnu.linkonce.h.*)
-    __XT_EXCEPTION_DESCS_END__ = ABSOLUTE(.);
-    *(.xt_except_desc_end)
-    *(.dynamic)
-    *(.gnu.version_d)
-    . = ALIGN(4);       /* this table MUST be 4-byte aligned */
-    _bss_table_start = ABSOLUTE(.);
-    LONG(_bss_start)
-    LONG(_bss_end)
-    _bss_table_end = ABSOLUTE(.);
-    _rodata_end = ABSOLUTE(.);
-  } >dram0_0_seg :dram0_0_phdr
-
-  .bss ALIGN(8) (NOLOAD) : ALIGN(4)
-  {
-    . = ALIGN (8);
-    _bss_start = ABSOLUTE(.);
-    *(.dynsbss)
-    *(.sbss)
-    *(.sbss.*)
-    *(.gnu.linkonce.sb.*)
-    *(.scommon)
-    *(.sbss2)
-    *(.sbss2.*)
-    *(.gnu.linkonce.sb2.*)
-    *(.dynbss)
-    *(.bss)
-    *(.bss.*)
-    *(.gnu.linkonce.b.*)
-    *(COMMON)
-    . = ALIGN (8);
-    _bss_end = ABSOLUTE(.);
-    _heap_start = ABSOLUTE(.);
-/*    _stack_sentry = ALIGN(0x8); */
-  } >dram0_0_seg :dram0_0_bss_phdr
-/* __stack = 0x3ffc8000; */
-
   .irom0.text : ALIGN(4)
   {
     _irom0_text_start = ABSOLUTE(.);
@@ -231,6 +165,7 @@ SECTIONS
     *(.literal .text .literal.* .text.* .stub .gnu.warning .gnu.linkonce.literal.* .gnu.linkonce.t.*.literal .gnu.linkonce.t.*)
     *.cpp.o(.iram.text)
     *.c.o(.iram.text)
+    *(.rodata._ZTV*) /* C++ vtables */
     /* PlatformIO */
     /* framework */
     *.pioenvs\\*\\lib*.a:(.iram.text)
@@ -249,6 +184,72 @@ SECTIONS
     _etext = .;
   } >iram1_0_seg :iram1_0_phdr
 
+  .rodata : ALIGN(4)
+  {
+    _rodata_start = ABSOLUTE(.);
+    *(.sdk.version)
+    *(.rodata)
+    *(.rodata.*)
+    *(.gnu.linkonce.r.*)
+    *(.rodata1)
+    __XT_EXCEPTION_TABLE__ = ABSOLUTE(.);
+    *(.xt_except_table)
+    *(.gcc_except_table)
+    *(.gnu.linkonce.e.*)
+    *(.gnu.version_r)
+    *(.eh_frame)
+    . = (. + 3) & ~ 3;
+    /*  C++ constructor and destructor tables, properly ordered:  */
+    __init_array_start = ABSOLUTE(.);
+    KEEP (*crtbegin.o(.ctors))
+    KEEP (*(EXCLUDE_FILE (*crtend.o) .ctors))
+    KEEP (*(SORT(.ctors.*)))
+    KEEP (*(.ctors))
+    __init_array_end = ABSOLUTE(.);
+    KEEP (*crtbegin.o(.dtors))
+    KEEP (*(EXCLUDE_FILE (*crtend.o) .dtors))
+    KEEP (*(SORT(.dtors.*)))
+    KEEP (*(.dtors))
+    /*  C++ exception handlers table:  */
+    __XT_EXCEPTION_DESCS__ = ABSOLUTE(.);
+    *(.xt_except_desc)
+    *(.gnu.linkonce.h.*)
+    __XT_EXCEPTION_DESCS_END__ = ABSOLUTE(.);
+    *(.xt_except_desc_end)
+    *(.dynamic)
+    *(.gnu.version_d)
+    . = ALIGN(4);       /* this table MUST be 4-byte aligned */
+    _bss_table_start = ABSOLUTE(.);
+    LONG(_bss_start)
+    LONG(_bss_end)
+    _bss_table_end = ABSOLUTE(.);
+    _rodata_end = ABSOLUTE(.);
+  } >dram0_0_seg :dram0_0_phdr
+
+  .bss ALIGN(8) (NOLOAD) : ALIGN(4)
+  {
+    . = ALIGN (8);
+    _bss_start = ABSOLUTE(.);
+    *(.dynsbss)
+    *(.sbss)
+    *(.sbss.*)
+    *(.gnu.linkonce.sb.*)
+    *(.scommon)
+    *(.sbss2)
+    *(.sbss2.*)
+    *(.gnu.linkonce.sb2.*)
+    *(.dynbss)
+    *(.bss)
+    *(.bss.*)
+    *(.gnu.linkonce.b.*)
+    *(COMMON)
+    . = ALIGN (8);
+    _bss_end = ABSOLUTE(.);
+    _heap_start = ABSOLUTE(.);
+/*    _stack_sentry = ALIGN(0x8); */
+  } >dram0_0_seg :dram0_0_bss_phdr
+/* __stack = 0x3ffc8000; */
+
   .lit4 : ALIGN(4)
   {
     _lit4_start = ABSOLUTE(.);