core: add new __lowmem macro to allocate a static lowmem buffer

Add a new __lowmem macro that can be applied to an uninitialized
static (or global) object, which allocates it in a new .lowmem section
allocated below the 1 MB boundary.  Keep in mind that low memory is
precious!

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

4 files changed, 25 insertions, 6 deletions

diff --git a/core/include/core.h b/core/include/core.h
index 0975ebf8..e61bf998 100644
--- a/core/include/core.h
+++ b/core/include/core.h
@@ -1,6 +1,7 @@
 #ifndef CORE_H
 #define CORE_H
 
+#include <klibc/compiler.h>
 #include <com32.h>
 
 extern char core_xfer_buf[65536];
@@ -12,4 +13,6 @@ int __cdecl core_cfarcall(uint32_t, const void *, uint32_t);
 
 void call16(void (*)(void), const com32sys_t *, com32sys_t *);
 
+#define __lowmem __attribute((nocommon,section(".lowmem")))
+
 #endif /* CORE_H */
diff --git a/core/init.inc b/core/init.inc
index 809fa8ee..ec8c7b3b 100644
--- a/core/init.inc
+++ b/core/init.inc
@@ -60,7 +60,6 @@ common_init:
 ; The code to decompress the PM code and initialize other segments.
 ;
 		extern _lzo1x_decompress_asm_fast
-		extern __uibss_auxseg_dwords
 
 		section .textnr
 		bits 32
@@ -83,8 +82,8 @@ pm_decompress:
 		mov edi,__bss16_start
 		mov ecx,__bss16_dwords
 		rep stosd
-		mov edi,__uibss_start
-		mov ecx,__uibss_auxseg_dwords
+		mov edi,__high_clear_start	; .uibss, .auxseg, .lowmem
+		mov ecx,__high_clear_dwords
 		rep stosd
 
 		ret
diff --git a/core/layout.inc b/core/layout.inc
index ec011f35..72236839 100644
--- a/core/layout.inc
+++ b/core/layout.inc
@@ -79,6 +79,8 @@ RBFG_brainfuck:	resb 2048		; Bigger than an Ethernet packet...
 		SECINFO replacestub
 
 		SECINFO pm_code
+		SECINFO high_clear
+
 		extern __bss_start, __bss_end, __bss_len, __bss_dwords
 
 		extern free_high_memory
diff --git a/core/syslinux.ld b/core/syslinux.ld
index eb0e4116..b931ed2e 100644
--- a/core/syslinux.ld
+++ b/core/syslinux.ld
@@ -148,6 +148,8 @@ SECTIONS
 	. = ALIGN(16);
 	__pm_code_lma = .;
 
+	__high_clear_start = .;
+
 	. = ALIGN(512);
 	.adv (NOLOAD) : {
 		__adv_start = .;
@@ -185,9 +187,22 @@ SECTIONS
 	__auxseg_len = __auxseg_end - __auxseg_start;
 	__auxseg_dwords = (__auxseg_len + 3) >> 2;
 	aux_seg = __auxseg_start >> 4;
-	
-	__uibss_auxseg_len = __auxseg_end - __uibss_start;
-	__uibss_auxseg_dwords = (__uibss_auxseg_len + 3) >> 2;
+
+	/*
+	 * Used to allocate lowmem buffers from 32-bit code
+	 */
+	.lowmem (NOLOAD) : {
+		__lowmem_start = .;
+		*(.lowmem)
+		__lowmem_end = .;
+	}
+	__lowmem_len = __lowmem_end - __lowmem_start;
+	__lowmem_dwords = (__lowmem_len + 3) >> 2;
+
+	__high_clear_end = .;
+
+	__high_clear_len = __high_clear_end - __high_clear_start;
+	__high_clear_dwords = (__high_clear_len + 3) >> 2;
 
 	/*
 	 * 32-bit code.  This is a hack for the moment due to the