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From: "arnd at linaro dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/94986] New: missing diagnostic on ARM thumb2 compilation with
 -pg when using r7 in inline asm
Date: Thu, 07 May 2020 15:59:46 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94986

            Bug ID: 94986
           Summary: missing diagnostic on ARM thumb2 compilation with -pg
                    when using r7 in inline asm
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: arnd at linaro dot org
  Target Milestone: ---

I reported a bug against clang for a Linux kernel failure, but=20
 it was suggested that the clang behavior is probably correct in this corner
case while gcc gets it wrong, see https://bugs.llvm.org/show_bug.cgi?id=3D4=
5826

echo 'void f(void) { asm("mov r7, #0" ::: "r7"); }' | arm-linux-gnueabi-gcc
-march=3Darmv7-a -O2  -mthumb -pg -S -xc -

silently accepts an inline asm statement that clobbers the frame pointer, b=
ut
gcc rejects the same code if any of '-O0', '-fomit-frame-pointer' or
'fno-omit-frame-pointer' are used:

<stdin>: In function 'f':
<stdin>:1:44: error: r7 cannot be used in 'asm' here

If using r7 in this case is indeed invalid, we need to ensure the kernel do=
es
not do this, and having gcc reject it would be helpful.=