[build] Use unique entry symbols for each prefix

Some binutils versions will drag in an object to satisfy the entry
symbol; some won't.  Try to cope with this exciting variety of
behaviour by ensuring that all entry symbols are unique.

Remove the explicit inclusion of the prefix object on the linker
command line, since the entry symbol now provides all the information
needed to identify the prefix.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/Makefile.housekeeping

 #		   ROM header (e.g."pci_vendor_id=0x1186 pci_device_id=0x1300")
 #
 TGT_LD_DRIVERS	= $(subst -,_,$(patsubst %,obj_%,$(TGT_DRIVERS)))
-TGT_LD_PREFIX	= obj_$(TGT_PREFIX)prefix
 TGT_LD_IDS	= pci_vendor_id=$(firstword $(TGT_PCI_VENDOR) 0) \
 		  pci_device_id=$(firstword $(TGT_PCI_DEVICE) 0)
+TGT_LD_ENTRY	= _$(TGT_PREFIX)_start
 
 # Calculate linker flags based on link-time options for the current
 # target type (e.g. "bin/dfe538--prism2_pci.zrom.tmp") and derive the
 #		 "-u obj_zpciprefix -u obj_rtl8139 -u obj_prism2_pci
 #		  --defsym pci_vendor=0x1186 --defsym pci_device=0x1300")
 #
-TGT_LD_FLAGS	= $(foreach SYM,$(TGT_LD_PREFIX) $(TGT_LD_DRIVERS) obj_config,\
+TGT_LD_FLAGS	= $(foreach SYM,$(TGT_LD_ENTRY) $(TGT_LD_DRIVERS) obj_config,\
 		    -u $(SYM) --defsym check_$(SYM)=$(SYM) ) \
 		  $(patsubst %,--defsym %,$(TGT_LD_IDS)) \
-		  $(TGT_LD_FLAGS_PRE)
+		  -e $(TGT_LD_ENTRY)
 
 # Calculate list of debugging versions of objects to be included in
 # the target.
 	@$(ECHO) 'PCI device           : $(TGT_PCI_DEVICE)'
 	@$(ECHO)
 	@$(ECHO) 'LD driver symbols    : $(TGT_LD_DRIVERS)'
-	@$(ECHO) 'LD prefix symbols    : $(TGT_LD_PREFIX)'
 	@$(ECHO) 'LD ID symbols        : $(TGT_LD_IDS)'
+	@$(ECHO) 'LD entry point       : $(TGT_LD_ENTRY)'
 	@$(ECHO)
 	@$(ECHO) 'LD target flags      : $(TGT_LD_FLAGS)'
 	@$(ECHO)

src/arch/i386/prefix/dskprefix.S

 	.text
 	.section ".prefix", "ax", @progbits
 	.code16
-	.globl	start
-start:
+	.globl	_dsk_start
+_dsk_start:
 
 	jmp	$BOOTSEG, $go		/* reload cs:ip to match relocation addr */
 go: 

src/arch/i386/prefix/hdprefix.S

 	.section ".prefix", "awx", @progbits
 	.code16
 	.org 0
-	.globl	start
-start:
+	.globl	_hd_start
+_hd_start:
 
 	movw	$load_image, %bp
 	jmp	find_active_partition

src/arch/i386/prefix/kkpxeprefix.S

 
 #define PXELOADER_KEEP_UNDI
 #define PXELOADER_KEEP_PXE
+#define _pxe_start _kkpxe_start
 #include "pxeprefix.S"

src/arch/i386/prefix/kpxeprefix.S

 FILE_LICENCE ( GPL2_OR_LATER )
 
 #define PXELOADER_KEEP_UNDI
+#define _pxe_start _kpxe_start
 #include "pxeprefix.S"

src/arch/i386/prefix/linuxprefix.S

 
 	.section ".text"
 	.code32
-	.globl _start
-	.type _start, @function
+	.globl _linux_start
+	.type _linux_start, @function
 
-_start:
+_linux_start:
 	xorl	%ebp, %ebp
 
 	popl	%esi       // save argc

src/arch/i386/prefix/lkrnprefix.S

 	.arch i386
 	.org	0
 	.section ".prefix", "ax", @progbits
-	.globl	start
-start:
+	.globl	_lkrn_start
+_lkrn_start:
 /* 
 	This is a minimal boot sector.	If anyone tries to execute it (e.g., if
 	a .lilo file is dd'ed to a floppy), print an error message. 

src/arch/i386/prefix/mromprefix.S

 #define PCI_BAR_EXPROM			0x30
 
 #define ROMPREFIX_EXCLUDE_PAYLOAD 1
+#define _rom_start _mrom_start
 #include "romprefix.S"
 
 	.text

src/arch/i386/prefix/nbiprefix.S

 	.byte	0
 	.byte	0		/* No flags */
 	.word	0x0000, 0x07c0	/* Load header to 0x07c0:0x0000 */
-	.word	start, 0x07c0	/* Start execution at 0x07c0:entry */
+	.word	_nbi_start, 0x07c0	/* Start execution at 0x07c0:entry */
 	.size	file_header, . - file_header
 
 /*****************************************************************************
  * NBI entry point
  *****************************************************************************
  */
-	.globl	start
-start:
+	.globl	_nbi_start
+_nbi_start:
 	/* Install iPXE */
 	call	install
 

src/arch/i386/prefix/pxeprefix.S

  *****************************************************************************
  */
 	.section ".prefix", "ax", @progbits
-	.globl	start
-start:
+	.globl	_pxe_start
+_pxe_start:
 	jmp	$0x7c0, $1f
 1:
 	/* Preserve registers for possible return to PXE */

src/arch/i386/prefix/romprefix.S

 	.code16
 	.arch i386
 	.section ".prefix", "ax", @progbits
-	.globl	start
-start:
+	.globl	_rom_start
+_rom_start:
 	
 	.org	0x00
 romheader:

src/arch/i386/scripts/i386-kir.lds

 
 OUTPUT_FORMAT ( "elf32-i386", "elf32-i386", "elf32-i386" )
 OUTPUT_ARCH ( i386 )
-ENTRY ( _entry )
 
 SECTIONS {
 

src/arch/i386/scripts/i386.lds

  *
  */
 
-ENTRY ( start )
-
 SECTIONS {
 
     /* Each section starts at a virtual address of zero.

src/arch/i386/scripts/linux.lds

 OUTPUT_FORMAT ( "elf32-i386", "elf32-i386", "elf32-i386" )
 OUTPUT_ARCH ( i386 )
 
-ENTRY ( _start )
-
 SECTIONS {
 	_max_align = 32;
 

src/arch/x86/Makefile.efi

 NON_AUTO_MEDIA	+= efi
 NON_AUTO_MEDIA	+= efidrv
 
-# Specify entry point
-#
-TGT_LD_FLAGS_PRE = -e _$(TGT_PREFIX)_start
-
 # Rules for building EFI files
 #
 $(BIN)/%.efi : $(BIN)/%.efi.tmp $(ELF2EFI)

src/arch/x86_64/prefix/linuxprefix.S

 
 	.section ".text"
 	.code64
-	.globl _start
-	.type _start, @function
+	.globl _linux_start
+	.type _linux_start, @function
 
-_start:
+_linux_start:
 	xorq	%rbp, %rbp
 
 	popq	%rdi       // argc -> C arg1

src/arch/x86_64/scripts/linux.lds

 OUTPUT_FORMAT ( "elf64-x86-64", "elf64-x86-64", "elf64-x86-64" )
 OUTPUT_ARCH ( i386:x86-64 )
 
-ENTRY ( _start )
-
 SECTIONS {
 	_max_align = 32;