Re: [kvm-unit-tests PATCH 4/4] x86: Extend ASM_TRY to handle #UD thrown by FEP-triggered emulator

[Paolo Bonzini <pbonzini@redhat.com>]

On 8/3/22 20:16, Sean Christopherson wrote:
>> While here, I've also took the opportunity to merge both 32 and 64-bit
>> versions of ASM_TRY() (.dc.a for .long and .quad), but perhaps there
>> were some reasons for not using .dc.a?
> This should be a separate patch, and probably as the very last patch in case dc.a
> isn't viable for whatever reason.  I've never seen/used dc.a so I really have no
> idea whether or not it's ok to use.

Yes, for now I'll squash this, which is similar to Michal's idea but 
using the trusty double underscore prefix:

diff --git a/lib/x86/desc.h b/lib/x86/desc.h
index 2a285eb..5b21820 100644
--- a/lib/x86/desc.h
+++ b/lib/x86/desc.h
@@ -81,11 +81,12 @@ typedef struct  __attribute__((packed)) {
  } tss64_t;

  #ifdef __x86_64
-#define ASM_TRY(catch)			\
+#define __ASM_TRY(prefix, catch)	\
  	"movl $0, %%gs:4 \n\t"		\
  	".pushsection .data.ex \n\t"	\
  	".quad 1111f, " catch "\n\t"	\
  	".popsection \n\t"		\
+	prefix "\n\t"			\
  	"1111:"
  #else
  #define ASM_TRY(catch)			\
@@ -96,6 +97,8 @@ typedef struct  __attribute__((packed)) {
  	"1111:"
  #endif

+#define ASM_TRY(catch) __ASM_TRY("", catch)
+
  /*
   * selector     32-bit                        64-bit
   * 0x00         NULL descriptor               NULL descriptor
diff --git a/x86/emulator.c b/x86/emulator.c
index df0bc49..6d2f166 100644
--- a/x86/emulator.c
+++ b/x86/emulator.c
@@ -19,6 +19,7 @@ static int exceptions;

  /* Forced emulation prefix, used to invoke the emulator 
unconditionally. */
  #define KVM_FEP "ud2; .byte 'k', 'v', 'm';"
+#define ASM_TRY_FEP(catch) __ASM_TRY(KVM_FEP, catch)

  struct regs {
  	u64 rax, rbx, rcx, rdx;
@@ -900,8 +901,8 @@ static void test_illegal_lea(void)
  {
  	unsigned int vector;

-	asm volatile (ASM_TRY("1f")
-		      KVM_FEP ".byte 0x8d; .byte 0xc0\n\t"
+	asm volatile (ASM_TRY_FEP("1f")
+		      ".byte 0x8d; .byte 0xc0\n\t"
  		      "1:"
  		      : : : "memory", "eax");


and the __ASM_SEL() idea can be sent as a separate patch.