From 238050dfd46e3c4a87329da1d48b4d8dde5af8a1 Mon Sep 17 00:00:00 2001 From: Michael Brown Date: Fri, 7 Jun 2013 13:46:27 +0100 Subject: [PATCH] [build] Work around bug in gcc >= 4.8 gcc 4.8 and 4.9 fail to compile pxe_call.c with the error "bp cannot be used in asm here". Other points in the codebase which use "ebp" in the asm clobber list do not seem to be affected. Unfortunately gcc provides no way to specify %ebp as an output register, so we cannot use this as a workaround. The only viable solution is to explicitly push/pop %ebp within the asm itself. This is ugly for two reasons: firstly, it may be unnecessary; secondly, it may cause gcc to generate invalid %esp-relative addresses if the asm happens to use memory operands. This specific block of asm uses no memory operands and so will not generate invalid code. Reported-by: Daniel P. Berrange Reported-by: Christian Hesse Originally-fixed-by: Christian Hesse Signed-off-by: Michael Brown --- src/arch/i386/interface/pxe/pxe_call.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/src/arch/i386/interface/pxe/pxe_call.c b/src/arch/i386/interface/pxe/pxe_call.c index 7fce75a9..a0743336 100644 --- a/src/arch/i386/interface/pxe/pxe_call.c +++ b/src/arch/i386/interface/pxe/pxe_call.c @@ -271,12 +271,14 @@ int pxe_start_nbp ( void ) { DBG ( "Restarting NBP (%x)\n", jmp ); /* Far call to PXE NBP */ - __asm__ __volatile__ ( REAL_CODE ( "movw %%cx, %%es\n\t" + __asm__ __volatile__ ( REAL_CODE ( "pushl %%ebp\n\t" /* gcc bug */ + "movw %%cx, %%es\n\t" "pushw %%es\n\t" "pushw %%di\n\t" "sti\n\t" "lcall $0, $0x7c00\n\t" - "addw $4, %%sp\n\t" ) + "popl %%ebp\n\t" /* discard */ + "popl %%ebp\n\t" /* gcc bug */ ) : "=a" ( status ), "=b" ( discard_b ), "=c" ( discard_c ), "=d" ( discard_d ), "=D" ( discard_D ) @@ -284,7 +286,7 @@ int pxe_start_nbp ( void ) { "c" ( rm_cs ), "d" ( virt_to_phys ( &pxenv ) ), "D" ( __from_text16 ( &ppxe ) ) - : "esi", "ebp", "memory" ); + : "esi", "memory" ); if ( status ) return -EPXENBP ( status );