[PATCH] x86emul/test: don't use *_len symbols

[PATCH] x86emul/test: don't use *_len symbols

[Jan Beulich]

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... as they don't work as intended with -fPIC.

I did prefer them over *_end ones at the time because older gcc would
cause .L* symbols to be public, due to issuing .globl for all
referenced externals. And labels at the end of instructions collide
with the ones at the start of the next instruction, making disassembly
harder to grok. Luckily recent gcc no longer issues those .globl
directives, and hence .L* labels, staying local by default, no longer
get in the way.

Reported-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/tools/tests/x86_emulator/test_x86_emulator.c
+++ b/tools/tests/x86_emulator/test_x86_emulator.c
@@ -885,17 +885,16 @@ int main(int argc, char **argv)
     }
     printf("okay\n");
 
-#define decl_insn(which) extern const unsigned char which[], which##_len[]
+#define decl_insn(which) extern const unsigned char which[], \
+                         which##_end[] asm ( ".L" #which "_end" )
 #define put_insn(which, insn) ".pushsection .test, \"ax\", @progbits\n" \
                               #which ": " insn "\n"                     \
-                              ".equ " #which "_len, .-" #which "\n"     \
+                              ".L" #which "_end:\n"                     \
                               ".popsection"
 #define set_insn(which) (regs.eip = (unsigned long)(which))
 #define valid_eip(which) (regs.eip >= (unsigned long)(which) && \
-                          regs.eip < (unsigned long)(which) + \
-                                      (unsigned long)which##_len)
-#define check_eip(which) (regs.eip == (unsigned long)(which) + \
-                                      (unsigned long)which##_len)
+                          regs.eip < (unsigned long)which##_end)
+#define check_eip(which) (regs.eip == (unsigned long)which##_end)
 
     printf("%-40s", "Testing andn (%edx),%ecx,%ebx...");
     if ( stack_exec && cpu_has_bmi1 )




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x86emul/test: don't use *_len symbols

... as they don't work as intended with -fPIC.

I did prefer them over *_end ones at the time because older gcc would
cause .L* symbols to be public, due to issuing .globl for all
referenced externals. And labels at the end of instructions collide
with the ones at the start of the next instruction, making disassembly
harder to grok. Luckily recent gcc no longer issues those .globl
directives, and hence .L* labels, staying local by default, no longer
get in the way.

Reported-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/tools/tests/x86_emulator/test_x86_emulator.c
+++ b/tools/tests/x86_emulator/test_x86_emulator.c
@@ -885,17 +885,16 @@ int main(int argc, char **argv)
     }
     printf("okay\n");
 
-#define decl_insn(which) extern const unsigned char which[], which##_len[]
+#define decl_insn(which) extern const unsigned char which[], \
+                         which##_end[] asm ( ".L" #which "_end" )
 #define put_insn(which, insn) ".pushsection .test, \"ax\", @progbits\n" \
                               #which ": " insn "\n"                     \
-                              ".equ " #which "_len, .-" #which "\n"     \
+                              ".L" #which "_end:\n"                     \
                               ".popsection"
 #define set_insn(which) (regs.eip = (unsigned long)(which))
 #define valid_eip(which) (regs.eip >= (unsigned long)(which) && \
-                          regs.eip < (unsigned long)(which) + \
-                                      (unsigned long)which##_len)
-#define check_eip(which) (regs.eip == (unsigned long)(which) + \
-                                      (unsigned long)which##_len)
+                          regs.eip < (unsigned long)which##_end)
+#define check_eip(which) (regs.eip == (unsigned long)which##_end)
 
     printf("%-40s", "Testing andn (%edx),%ecx,%ebx...");
     if ( stack_exec && cpu_has_bmi1 )

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Re: [PATCH] x86emul/test: don't use *_len symbols

[Wei Liu]

On Tue, Jan 24, 2017 at 08:02:23AM -0700, Jan Beulich wrote:
> ... as they don't work as intended with -fPIC.
> 
> I did prefer them over *_end ones at the time because older gcc would
> cause .L* symbols to be public, due to issuing .globl for all
> referenced externals. And labels at the end of instructions collide
> with the ones at the start of the next instruction, making disassembly
> harder to grok. Luckily recent gcc no longer issues those .globl
> directives, and hence .L* labels, staying local by default, no longer
> get in the way.
> 
> Reported-by: Wei Liu <wei.liu2@citrix.com>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> 

Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Tested-by: Wei Liu <wei.liu2@citrix.com>

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