Bug 905862

Summary: gcc 4.8 regression: ‘asm’ operand has impossible constraints
Product: [Fedora] Fedora Reporter: Sandro Mani <manisandro>
Component: gccAssignee: Jakub Jelinek <jakub>
Status: CLOSED UPSTREAM QA Contact: Fedora Extras Quality Assurance <extras-qa>
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Version: rawhideCC: jakub, law, valdis.kletnieks
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Last Closed: 2013-01-30 12:02:58 UTC Type: Bug
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Preprocessed testcase none

Description Sandro Mani 2013-01-30 10:47:32 UTC 
Created attachment 690281 [details]
Preprocessed testcase

Description of problem:
Inline assembler in attached testcase (which is a stripped down code section from the vbox kmod) fails to compile with gcc 4.8.

Version-Release number of selected component (if applicable):
gcc-4.8.0-0.6.fc19.x86_64

How reproducible:
Always

Steps to Reproduce:
1. grab attached testcase
2. gcc -Wall -O2 -c -o test.o test.i
  
Actual results:
$ gcc -Wall -O2 -c -o test.o test.i
test.c: In function ‘test’:
test.c:14:9: error: ‘asm’ operand has impossible constraints
         __asm__ __volatile__("repe; scasl\n\t"

Additional info:
- code trimmed for 64bit CPU
- error triggers only with optimization enabled (-O1, -O2, -O3, -Os, -Ofast)
- testcase works with gcc version 4.7.2 20121109 (Red Hat 4.7.2-9) (GCC)
Comment 1 Jakub Jelinek 2013-01-30 12:02:58 UTC 
Tracking this upstream.
Comment 2 Valdis Kletnieks 2013-02-19 04:53:12 UTC 
For what it's worth, confirming that the vbox module in question now compiles with gcc-4.8.0-0.13.fc19.x86_64