[build] Work around bug in gcc >= 4.8

Commit 238050d ("[build] Work around bug in gcc >= 4.8") works around
one instance of a bug in recent versions of gcc, in which "ebp" cannot
be specified within an asm clobber list.

Some versions of gcc seem to exhibit the same bug on other points in
the codebase.  Fix by changing all instances of "ebp" in a clobber
list to use the push/pop %ebp workaround instead.

Originally-implemented-by: Víctor Román Archidona <contacto@victor-roman.es>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/i386/drivers/net/undiload.c

 
 	/* Call loader */
 	undi_loader_entry = undirom->loader_entry;
-	__asm__ __volatile__ ( REAL_CODE ( "pushw %%ds\n\t"
+	__asm__ __volatile__ ( REAL_CODE ( "pushl %%ebp\n\t" /* gcc bug */
+					   "pushw %%ds\n\t"
 					   "pushw %%ax\n\t"
 					   "lcall *undi_loader_entry\n\t"
-					   "addw $4, %%sp\n\t" )
+					   "popl %%ebp\n\t" /* discard */
+					   "popl %%ebp\n\t" /* gcc bug */ )
 			       : "=a" ( exit )
 			       : "a" ( __from_data16 ( &undi_loader ) )
-			       : "ebx", "ecx", "edx", "esi", "edi", "ebp" );
+			       : "ebx", "ecx", "edx", "esi", "edi" );
 
 	if ( exit != PXENV_EXIT_SUCCESS ) {
 		/* Clear entry point */

src/arch/i386/firmware/pcbios/bios_console.c

 		return;
 
 	/* Print character with attribute */
-	__asm__ __volatile__ ( REAL_CODE ( "sti\n\t"
+	__asm__ __volatile__ ( REAL_CODE ( "pushl %%ebp\n\t" /* gcc bug */
+					   "sti\n\t"
 					   /* Skip non-printable characters */
 					   "cmpb $0x20, %%al\n\t"
 					   "jb 1f\n\t"
 					   "xorw %%bx, %%bx\n\t"
 					   "movb $0x0e, %%ah\n\t"
 					   "int $0x10\n\t"
-					   "cli\n\t" )
+					   "cli\n\t"
+					   "popl %%ebp\n\t" /* gcc bug */ )
 			       : "=a" ( discard_a ), "=b" ( discard_b ),
 			         "=c" ( discard_c )
-			       : "a" ( character ), "b" ( bios_attr )
-			       : "ebp" );
+			       : "a" ( character ), "b" ( bios_attr ) );
 }
 
 /**

src/arch/i386/image/bootsector.c

 					   "movw %%ss, %%ax\n\t"
 					   "movw %%ax, %%cs:saved_ss\n\t"
 					   "movw %%sp, %%cs:saved_sp\n\t"
+					   /* Save frame pointer (gcc bug) */
+					   "movl %%ebp, %%cs:saved_ebp\n\t"
 					   /* Prepare jump to boot sector */
 					   "pushw %%bx\n\t"
 					   "pushw %%di\n\t"
 					   "sti\n\t"
 					   "lret\n\t"
 					   /* Preserved variables */
+					   "\nsaved_ebp: .long 0\n\t"
 					   "\nsaved_ss: .word 0\n\t"
 					   "\nsaved_sp: .word 0\n\t"
 					   "\nsaved_retaddr: .word 0\n\t"
 					   /* Boot failure return point */
 					   "\nbootsector_exec_fail:\n\t"
+					   /* Restore frame pointer (gcc bug) */
+					   "movl %%cs:saved_ebp, %%ebp\n\t"
 					   /* Restore stack pointer */
 					   "movw %%cs:saved_ss, %%ax\n\t"
 					   "movw %%ax, %%ss\n\t"
 			         "=d" ( discard_d )
 			       : "b" ( segment ), "D" ( offset ),
 			         "d" ( drive )
-			       : "eax", "ecx", "esi", "ebp" );
+			       : "eax", "ecx", "esi" );
 
 	DBG ( "Booted disk returned via INT 18 or 19\n" );
 

src/arch/i386/image/elfboot.c

 
 	/* Jump to OS with flat physical addressing */
 	DBGC ( image, "ELF %p starting execution at %lx\n", image, entry );
-	__asm__ __volatile__ ( PHYS_CODE ( "call *%%edi\n\t" )
+	__asm__ __volatile__ ( PHYS_CODE ( "pushl %%ebp\n\t" /* gcc bug */
+					   "call *%%edi\n\t"
+					   "popl %%ebp\n\t" /* gcc bug */ )
 			       : : "D" ( entry )
-			       : "eax", "ebx", "ecx", "edx", "esi", "ebp",
-			         "memory" );
+			       : "eax", "ebx", "ecx", "edx", "esi", "memory" );
 
 	DBGC ( image, "ELF %p returned\n", image );
 

src/arch/i386/image/nbi.c

 	       imgheader->execaddr.segoff.offset );
 
 	__asm__ __volatile__ (
-		REAL_CODE ( "pushw %%ds\n\t"	/* far pointer to bootp data */
+		REAL_CODE ( "pushl %%ebp\n\t"	/* gcc bug */
+			    "pushw %%ds\n\t"	/* far pointer to bootp data */
 			    "pushw %%bx\n\t"
 			    "pushl %%esi\n\t"	/* location */
 			    "pushw %%cs\n\t"	/* lcall execaddr */
 			    "pushl %%edi\n\t"
 			    "lret\n\t"
 			    "\n2:\n\t"
-			    "addw $8,%%sp\n\t"	/* clean up stack */ )
+			    "addw $8,%%sp\n\t"	/* clean up stack */
+			    "popl %%ebp\n\t"	/* gcc bug */ )
 		: "=a" ( rc ), "=D" ( discard_D ), "=S" ( discard_S ),
 		  "=b" ( discard_b )
 		: "D" ( imgheader->execaddr.segoff ),
 		  "S" ( imgheader->location ),
 		  "b" ( __from_data16 ( basemem_packet ) )
-		: "ecx", "edx", "ebp" );
+		: "ecx", "edx" );
 
 	return rc;
 }
 
 	/* Jump to OS with flat physical addressing */
 	__asm__ __volatile__ (
-		PHYS_CODE ( "pushl %%ebx\n\t" /* bootp data */
+		PHYS_CODE ( "pushl %%ebp\n\t" /* gcc bug */
+			    "pushl %%ebx\n\t" /* bootp data */
 			    "pushl %%esi\n\t" /* imgheader */
 			    "pushl %%eax\n\t" /* loaderinfo */
 			    "call *%%edi\n\t"
-			    "addl $12, %%esp\n\t" /* clean up stack */ )
+			    "addl $12, %%esp\n\t" /* clean up stack */
+			    "popl %%ebp\n\t" /* gcc bug */ )
 		: "=a" ( rc ), "=D" ( discard_D ), "=S" ( discard_S ),
 		  "=b" ( discard_b )
 		: "D" ( imgheader->execaddr.linear ),
 			imgheader->location.offset ),
 		  "b" ( virt_to_phys ( basemem_packet ) ),
 		  "a" ( virt_to_phys ( &loaderinfo ) )
-		: "ecx", "edx", "ebp", "memory" );
+		: "ecx", "edx", "memory" );
 
 	return rc;
 }

src/arch/i386/interface/pxeparent/pxeparent.c

 	/* Call real-mode entry point.  This calling convention will
 	 * work with both the !PXE and the PXENV+ entry points.
 	 */
-	__asm__ __volatile__ ( REAL_CODE ( "pushw %%es\n\t"
+	__asm__ __volatile__ ( REAL_CODE ( "pushl %%ebp\n\t" /* gcc bug */
+					   "pushw %%es\n\t"
 					   "pushw %%di\n\t"
 					   "pushw %%bx\n\t"
 					   "lcall *pxeparent_entry_point\n\t"
-					   "addw $6, %%sp\n\t" )
+					   "addw $6, %%sp\n\t"
+					   "popl %%ebp\n\t" /* gcc bug */ )
 			       : "=a" ( exit ), "=b" ( discard_b ),
 			         "=D" ( discard_D )
 			       : "b" ( function ),
 			         "D" ( __from_data16 ( &pxeparent_params ) )
-			       : "ecx", "edx", "esi", "ebp" );
+			       : "ecx", "edx", "esi" );
 
 	/* Determine return status code based on PXENV_EXIT and
 	 * PXENV_STATUS