Re: [Qemu-devel] [PATCH] kvm-unittest: fix build with gcc 4.3.X and older

[Gleb Natapov <gleb@redhat.com>]

On Wed, Oct 16, 2013 at 10:46:53PM +0300, Michael S. Tsirkin wrote:
> Old GCC didn't let you reference variable by
> number if it is listed with a specific register
> constraint, on the assumption you can just
> use the register name explicitly.
> 
> Build fails with errors like this:
> a.c:6: error: invalid 'asm': invalid operand code 'd'
> 
Is it worth to support such ancient compiler? Nobody complained till
now. BTW with your patch I still cannot compile with 4.2:

x86/s3.c: In function 'main':
x86/s3.c:145: error: inconsistent operand constraints in an 'asm'

> To fix, let's just use %eax %al etc.
> 
Only %d0 does not work and dropping "d" fixes it since compiler can
figure out correct register from variable size. The patch bellow fixes
compilation for 4.2.
 
diff --git a/lib/x86/pci.c b/lib/x86/pci.c
index f95cd88..231668a 100644
--- a/lib/x86/pci.c
+++ b/lib/x86/pci.c
@@ -3,13 +3,13 @@
 
 static void outl(unsigned short port, unsigned val)
 {
-    asm volatile("outl %d0, %w1" : : "a"(val), "Nd"(port));
+    asm volatile("outl %0, %w1" : : "a"(val), "Nd"(port));
 }
 
 static unsigned inl(unsigned short port)
 {
     unsigned data;
-    asm volatile("inl %w1, %d0" : "=a"(data) : "Nd"(port));
+    asm volatile("inl %w1, %0" : "=a"(data) : "Nd"(port));
     return data;
 }
 static uint32_t pci_config_read(pcidevaddr_t dev, uint8_t reg)
diff --git a/x86/s3.c b/x86/s3.c
index 71d3ff9..d568aa7 100644
--- a/x86/s3.c
+++ b/x86/s3.c
@@ -143,14 +143,14 @@ static inline int rtc_in(u8 reg)
 {
     u8 x = reg;
     asm volatile("outb %b1, $0x70; inb $0x71, %b0"
-		 : "+a"(x) : "0"(x));
+		 : "=a"(x) : "0"(x));
     return x;
 }
 
 static inline void rtc_out(u8 reg, u8 val)
 {
     asm volatile("outb %b1, $0x70; mov %b2, %b1; outb %b1, $0x71"
-		 : "+a"(reg) : "0"(reg), "ri"(val));
+		 : "=a"(reg) : "0"(reg), "ri"(val));
 }
 
 extern char resume_start, resume_end;
diff --git a/x86/vmexit.c b/x86/vmexit.c
index 3b945de..7e9af15 100644
--- a/x86/vmexit.c
+++ b/x86/vmexit.c
@@ -26,7 +26,7 @@ static void outw(unsigned short port, unsigned val)
 
 static void outl(unsigned short port, unsigned val)
 {
-    asm volatile("outl %d0, %w1" : : "a"(val), "Nd"(port));
+    asm volatile("outl %0, %w1" : : "a"(val), "Nd"(port));
 }
 
 static unsigned int inb(unsigned short port)
--
			Gleb.