esp32: Provision to redirect .bss to external ram through linker fragments

Include external ram section in the linker template to process it
through linker script generation mechanism. This enables redirection of .bss section to external memory using linker fragments

libnet80211, libpp, libbt, liblwip: Redirect .bss through fragments

components/bt/CMakeLists.txt

@@ -564,7 +564,8 @@ idf_component_register(SRCS "${srcs}"
                 INCLUDE_DIRS "${include_dirs}"
                 PRIV_INCLUDE_DIRS "${priv_include_dirs}"
                 REQUIRES nvs_flash soc esp_timer esp_pm
-                PRIV_REQUIRES esp_ipc)
+                PRIV_REQUIRES esp_ipc
+                LDFRAGMENTS "linker.lf")
 
 if(CONFIG_BT_ENABLED)
     target_compile_options(${COMPONENT_LIB} PRIVATE -Wno-implicit-fallthrough -Wno-unused-const-variable)

components/bt/linker.lf

@@ -0,0 +1,5 @@
+[mapping:bt]
+archive: libbt.a
+entries:
+    if SPIRAM_ALLOW_BSS_SEG_EXTERNAL_MEMORY = y:
+        * (extram_bss)

components/esp32/CMakeLists.txt

@@ -42,12 +42,6 @@ else()
 
     target_linker_script(${COMPONENT_LIB} INTERFACE "${CMAKE_CURRENT_BINARY_DIR}/esp32_out.ld")
 
-
-    if(CONFIG_SPIRAM_ALLOW_BSS_SEG_EXTERNAL_MEMORY)
-        # This has to be linked before esp32.project.ld
-        target_linker_script(${COMPONENT_LIB} INTERFACE "ld/esp32.extram.bss.ld")
-    endif()
-
     # Process the template file through the linker script generation mechanism, and use the output for linking the
     # final binary
     target_linker_script(${COMPONENT_LIB} INTERFACE "${CMAKE_CURRENT_LIST_DIR}/ld/esp32.project.ld.in"

components/esp32/component.mk

@@ -4,11 +4,6 @@
 
 COMPONENT_SRCDIRS := .
 
-ifdef CONFIG_SPIRAM_ALLOW_BSS_SEG_EXTERNAL_MEMORY
-   # This linker script must come before esp32.project.ld
-   LINKER_SCRIPTS += esp32.extram.bss.ld
-endif
-
 #Linker scripts used to link the final application.
 #Warning: These linker scripts are only used when the normal app is compiled; the bootloader
 #specifies its own scripts.

components/esp32/ld/esp32.extram.bss.ld

@@ -1,18 +0,0 @@
-/* This section is only included if CONFIG_SPIRAM_ALLOW_BSS_SEG_EXTERNAL_MEMORY
-   is set, to link some sections to BSS in PSRAM */
-
-SECTIONS
-{
-   /* external memory bss, from any global variable with EXT_RAM_ATTR attribute*/
-  .ext_ram.bss (NOLOAD) :
-  {
-    _ext_ram_bss_start = ABSOLUTE(.);
-    *(.ext_ram.bss*)
-    *libnet80211.a:(.dynsbss .sbss .sbss.* .gnu.linkonce.sb.* .scommon .sbss2.* .gnu.linkonce.sb2.* .dynbss .bss .bss.* .share.mem .gnu.linkonce.b.* COMMON)
-    *libpp.a:(.dynsbss .sbss .sbss.* .gnu.linkonce.sb.* .scommon .sbss2.* .gnu.linkonce.sb2.* .dynbss .bss .bss.* .share.mem .gnu.linkonce.b.* COMMON)
-    *liblwip.a:(.dynsbss .sbss .sbss.* .gnu.linkonce.sb.* .scommon .sbss2.* .gnu.linkonce.sb2.* .dynbss .bss .bss.* .share.mem .gnu.linkonce.b.* COMMON)
-    *libbt.a:(EXCLUDE_FILE (libbtdm_app.a) .dynsbss .sbss .sbss.* .gnu.linkonce.sb.* .scommon .sbss2.* .gnu.linkonce.sb2.* .dynbss .bss .bss.* .share.mem .gnu.linkonce.b.* COMMON)
-    . = ALIGN(4);
-    _ext_ram_bss_end = ABSOLUTE(.);
-  } > extern_ram_seg
-}

components/esp32/ld/esp32.project.ld.in

@@ -232,12 +232,22 @@ SECTIONS
     _noinit_end = ABSOLUTE(.);
   } > dram0_0_seg
 
+   /* external memory bss, from any global variable with EXT_RAM_ATTR attribute*/
+  .ext_ram.bss (NOLOAD) :
+  {
+    _ext_ram_bss_start = ABSOLUTE(.);
+
+    mapping[extern_ram]
+
+    . = ALIGN(4);
+    _ext_ram_bss_end = ABSOLUTE(.);
+  } > extern_ram_seg
+
   /* Shared RAM */
   .dram0.bss (NOLOAD) :
   {
     . = ALIGN (8);
     _bss_start = ABSOLUTE(.);
-    *(.ext_ram.bss*)
     _bt_bss_start = ABSOLUTE(.);
     *libbt.a:(.bss .bss.* COMMON)
     . = ALIGN (4);
@@ -253,18 +263,6 @@ SECTIONS
 
     mapping[dram0_bss]
 
-    *(.dynsbss)
-    *(.sbss)
-    *(.sbss.*)
-    *(.gnu.linkonce.sb.*)
-    *(.scommon)
-    *(.sbss2)
-    *(.sbss2.*)
-    *(.gnu.linkonce.sb2.*)
-    *(.dynbss)
-    *(.share.mem)
-    *(.gnu.linkonce.b.*)
-
     . = ALIGN (8);
     _bss_end = ABSOLUTE(.);
   } > dram0_0_seg

components/esp32/ld/esp32_fragments.lf

@@ -15,6 +15,18 @@ entries:
 entries:
     COMMON
 
+[sections:legacy_bss]
+entries:
+    .dynsbss
+    .sbss+
+    .gnu.linkonce.sb+
+    .scommon
+    .sbss2+
+    .gnu.linkonce.sb2+
+    .dynbss
+    .share.mem
+    .gnu.linkonce.b+
+
 [sections:rodata]
 entries:
     .rodata+
@@ -64,6 +76,10 @@ entries:
 entries:
     .iram.bss+
 
+[sections:extram_bss]
+entries:
+    .ext_ram.bss+
+
 [sections:dram]
 entries:
     .dram1+
@@ -87,6 +103,11 @@ entries:
     data -> dram0_data
     bss -> dram0_bss
     common -> dram0_bss
+    if SPIRAM_ALLOW_BSS_SEG_EXTERNAL_MEMORY = y:
+        extram_bss -> extern_ram
+    else:
+        extram_bss -> dram0_bss
+    legacy_bss -> dram0_bss
     iram -> iram0_text
     iram_data -> iram0_data
     iram_bss -> iram0_bss
@@ -130,3 +151,8 @@ entries:
 [scheme:wifi_rx_iram]
 entries:
     wifi_rx_iram -> iram0_text
+
+[scheme:extram_bss]
+entries:
+    bss -> extern_ram
+    common -> extern_ram

components/esp_common/Kconfig.spiram.common

@@ -94,6 +94,9 @@ config SPIRAM_ALLOW_BSS_SEG_EXTERNAL_MEMORY
     default n
     depends on SPIRAM
     help
-        If enabled the option,and add EXT_RAM_ATTR defined your variable,then your variable will be placed in
-        PSRAM instead of internal memory, and placed most of variables of lwip,net802.11,pp,bluedroid library
-        to external memory defaultly.
+        If enabled, variables with EXT_RAM_ATTR attribute will be placed in SPIRAM instead of internal DRAM.
+        BSS section of `lwip`, `net80211`, `pp`, `bt` libraries will be automatically placed
+        in SPIRAM. BSS sections from other object files and libraries can also be placed in SPIRAM through
+        linker fragment scheme `extram_bss`.
+
+        Note that the variables placed in SPIRAM using EXT_RAM_ATTR will be zero initialized.

components/esp_wifi/linker.lf

@@ -17,6 +17,9 @@ entries:
     if ESP32_WIFI_RX_IRAM_OPT = y:
         * (wifi_rx_iram)
 
+    if SPIRAM_ALLOW_BSS_SEG_EXTERNAL_MEMORY = y:
+        * (extram_bss)
+
 [mapping:net80211]
 archive: libnet80211.a
 entries:
@@ -25,3 +28,6 @@ entries:
 
     if ESP32_WIFI_RX_IRAM_OPT = y:
         * (wifi_rx_iram)
+
+    if SPIRAM_ALLOW_BSS_SEG_EXTERNAL_MEMORY = y:
+        * (extram_bss)

components/lwip/linker.lf

@@ -85,3 +85,6 @@ entries:
   else:
 
     * (default)
+
+  if SPIRAM_ALLOW_BSS_SEG_EXTERNAL_MEMORY = y:
+    * (extram_bss)

docs/en/api-guides/external-ram.rst

@@ -95,6 +95,8 @@ If enabled, a region of the address space starting from 0x3F800000 will be used
 
 Additional data can be moved from the internal BSS segment to external RAM by applying the macro ``EXT_RAM_ATTR`` to any static declaration (which is not initialized to a non-zero value).
 
+It is also possible to place the BSS section of a component or a library to external RAM using linker fragment scheme ``extram_bss``.
+
 This option reduces the internal static memory used by the BSS segment.
 
 Remaining external RAM can also be added to the capability heap allocator using the method shown above.