Re: [Qemu-devel] [PULL 00/31] Misc changes for 2016-05-27

[Richard W.M. Jones]

On Fri, May 27, 2016 at 02:04:52PM +0100, Peter Maydell wrote:
> With V=1:
> 
> i686-w64-mingw32-ld -m i386pe -Ttext 0 -e _start -s -o
> linuxboot_dma.img linuxboot_dma.o
> linuxboot_dma.o:linuxboot_dma.c:(.text+0x57): undefined reference to
> `load_kernel'
> 
> Building an image for the target using our host compiler seems like
> an odd choice,

Which compiler should I be using?

> but the makefile obviously intends to support it
> since it has specific ifdef CONFIG_WIN32 code to adjust the linker
> command line.
>
> I suspect this is a mismatch between the symbol the native asm is
> using and the one that the C compiler wants:
> 
> $ nm build/w32-new/pc-bios/optionrom/linuxboot_dma.o |grep load_kernel
> 000005dd T _load_kernel
>          U load_kernel
> 
> since name mangling rules are different for Linux and Windows ABIs.

One way to solve this (which works for me) is as below.  There are
some other approaches, eg. using -fno-leading-underscore, or using a
conditional macro to mangle the name.  However I have no idea if there
is some preferred way.

Rich.

diff --git a/pc-bios/optionrom/linuxboot_dma.c 
b/pc-bios/optionrom/linuxboot_dma.c
index 86ef1ce..8509b28 100644
--- a/pc-bios/optionrom/linuxboot_dma.c
+++ b/pc-bios/optionrom/linuxboot_dma.c
@@ -213,6 +213,9 @@ static uint32_t get_e801_addr(void)
     return ret;
 }
 
+/* Force the asm name without leading underscore, even on Win32. */
+extern void load_kernel(void) asm("load_kernel");
+
 void load_kernel(void)
 {
     void *setup_addr;


-- 
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