Re: [Xen-devel] [PATCH v4 06/34] x86/arm: Add BUGFRAME_NR define and BUILD checks.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Mar 18, 2016 at 06:40:31AM -0600, Jan Beulich wrote:
> >>> On 15.03.16 at 18:56, <konrad.wilk@xxxxxxxxxx> wrote:
> > --- a/xen/include/asm-arm/bug.h
> > +++ b/xen/include/asm-arm/bug.h
> > @@ -31,6 +31,7 @@ struct bug_frame {
> >  #define BUGFRAME_warn   0
> >  #define BUGFRAME_bug    1
> >  #define BUGFRAME_assert 2
> > +#define BUGFRAME_NR     3
> >  
> >  /* Many versions of GCC doesn't support the asm %c parameter which would
> >   * be preferable to this unpleasantness. We use mergeable string
> > @@ -39,6 +40,7 @@ struct bug_frame {
> >   */
> >  #define BUG_FRAME(type, line, file, has_msg, msg) do {                     
> >  \
> >      BUILD_BUG_ON((line) >> 16);                                            
> >  \
> > +    BUILD_BUG_ON(type >= BUGFRAME_NR);                                     
> >  \
> 
> The x86 variant has type properly parenthesized - why not here?
> 
> > --- a/xen/include/asm-x86/bug.h
> > +++ b/xen/include/asm-x86/bug.h
> > @@ -9,7 +9,7 @@
> >  #define BUGFRAME_warn   1
> >  #define BUGFRAME_bug    2
> >  #define BUGFRAME_assert 3
> > -
> > +#define BUGFRAME_NR     4
> >  #ifndef __ASSEMBLY__
> 
> Please retain the blank line.
> 
> > @@ -51,6 +51,7 @@ struct bug_frame {
> >  
> >  #define BUG_FRAME(type, line, ptr, second_frame, msg) do {                 
> >   \
> >      BUILD_BUG_ON((line) >> (BUG_LINE_LO_WIDTH + BUG_LINE_HI_WIDTH));       
> >   \
> > +    BUILD_BUG_ON((type) >= (BUGFRAME_NR));                                 
> >   \
> 
> The ARM variant has BUGFRAME_NR properly un-parenthesized -
> why here?

I know I copied and pasted it and I must have done something uncanny.

Anyhow this is what the change looks like now (I've retained the Reviewed
and Ack as I think this change is mostly cosmetical in nature?)

From 123ad665b283f8c59688bd86be0bbe79ce5723bb Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Thu, 10 Mar 2016 16:45:31 -0500
Subject: [PATCH] x86/arm: Add BUGFRAME_NR define and BUILD checks.

So that we have a nice mechansim to figure out the upper
bounds of bug.frames and also catch compiler errors in case
one tries to use a higher frame number.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Acked-by: Julien Grall <julien.grall@xxxxxxx>

---
Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

v3: First time included.
v4: Add BUG_FRAME check also in the assembler version of the macro.
v5: Add Acks, make BUILD_BUG_ON checks look correct. Position the
    BUGFRAME_NR properly.
---
---
 xen/include/asm-arm/bug.h | 3 +++
 xen/include/asm-x86/bug.h | 7 +++++++
 2 files changed, 10 insertions(+)

diff --git a/xen/include/asm-arm/bug.h b/xen/include/asm-arm/bug.h
index ab9e811..68353e1 100644
--- a/xen/include/asm-arm/bug.h
+++ b/xen/include/asm-arm/bug.h
@@ -32,6 +32,8 @@ struct bug_frame {
 #define BUGFRAME_bug    1
 #define BUGFRAME_assert 2
 
+#define BUGFRAME_NR     3
+
 /* Many versions of GCC doesn't support the asm %c parameter which would
  * be preferable to this unpleasantness. We use mergeable string
  * sections to avoid multiple copies of the string appearing in the
@@ -39,6 +41,7 @@ struct bug_frame {
  */
 #define BUG_FRAME(type, line, file, has_msg, msg) do {                      \
     BUILD_BUG_ON((line) >> 16);                                             \
+    BUILD_BUG_ON((type) >= BUGFRAME_NR);                                    \
     asm ("1:"BUG_INSTR"\n"                                                  \
          ".pushsection .rodata.str, \"aMS\", %progbits, 1\n"                \
          "2:\t.asciz " __stringify(file) "\n"                               \
diff --git a/xen/include/asm-x86/bug.h b/xen/include/asm-x86/bug.h
index e868e85..7825565 100644
--- a/xen/include/asm-x86/bug.h
+++ b/xen/include/asm-x86/bug.h
@@ -10,6 +10,7 @@
 #define BUGFRAME_bug    2
 #define BUGFRAME_assert 3
 
+#define BUGFRAME_NR     4
 #ifndef __ASSEMBLY__
 
 struct bug_frame {
@@ -51,6 +52,7 @@ struct bug_frame {
 
 #define BUG_FRAME(type, line, ptr, second_frame, msg) do {                   \
     BUILD_BUG_ON((line) >> (BUG_LINE_LO_WIDTH + BUG_LINE_HI_WIDTH));         \
+    BUILD_BUG_ON((type) >= BUGFRAME_NR);                                     \
     asm volatile ( _ASM_BUGFRAME_TEXT(second_frame)                          \
                    :: _ASM_BUGFRAME_INFO(type, line, ptr, msg) );            \
 } while (0)
@@ -83,6 +85,11 @@ extern const struct bug_frame __start_bug_frames[],
  * in .rodata
  */
     .macro BUG_FRAME type, line, file_str, second_frame, msg
+
+    .if \type >= BUGFRAME_NR
+        .error "Invalid BUGFRAME index"
+    .endif
+
     .L\@ud: ud2a
 
     .pushsection .rodata.str1, "aMS", @progbits, 1
-- 
2.5.0


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