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Re: [PATCH 1/4] pc-bios/s390-ccw: Silence warning from Clang by marking

From: Thomas Huth
Subject: Re: [PATCH 1/4] pc-bios/s390-ccw: Silence warning from Clang by marking panic() as noreturn
Date: Mon, 3 May 2021 06:53:30 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.0

On 02/05/2021 20.57, Philippe Mathieu-Daudé wrote:
On 5/2/21 7:48 PM, Thomas Huth wrote:
When compiling the s390-ccw bios with Clang, the compiler emits a warning:

  pc-bios/s390-ccw/main.c:210:5: warning: variable 'found' is used uninitialized
   whenever switch default is taken [-Wsometimes-uninitialized]
  pc-bios/s390-ccw/main.c:214:16: note: uninitialized use occurs here
      IPL_assert(found, "Boot device not found\n");

It's a false positive, it only happens because Clang is not smart enough
to see that the panic() function in the "default:" case can never return.

Anyway, let's explicitely mark panic() with "noreturn" to shut up the

Why not simply initialize the variable instead?

First, it's a false positive. If you only look at the code, someone might later wonder whether it's really necessary or not and try to remove it again (and since there is no warning with gcc, this patch would also have a good chance to get merged, bringing us back to where we are right now).

Second, declaring panic() as noreturn is certainly more sustainable, since it might prevent similar situations in other parts of the code in the future.


Signed-off-by: Thomas Huth <thuth@redhat.com>
  pc-bios/s390-ccw/s390-ccw.h | 1 +
  1 file changed, 1 insertion(+)

diff --git a/pc-bios/s390-ccw/s390-ccw.h b/pc-bios/s390-ccw/s390-ccw.h
index 6cd92669e9..79db69ff54 100644
--- a/pc-bios/s390-ccw/s390-ccw.h
+++ b/pc-bios/s390-ccw/s390-ccw.h
@@ -89,6 +89,7 @@ bool menu_is_enabled_enum(void);
#define MAX_BOOT_ENTRIES 31 +__attribute__ ((__noreturn__))
  static inline void panic(const char *string)

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