https://llvm.org/bugs/show_bug.cgi?id=30533
Bug ID: 30533
Summary: -Wformat check is not correct when using bitfield
parameters
Product: clang
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Frontend
Assignee: unassignedclangb...@nondot.org
Reporter: arichardson....@gmail.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
I noticed that one of my printfs was outputting garbage values even though I
compile with -Werror=format.
Abbreviated example:
struct foo {
uint64_t a : 10;
uint64_t b : 12;
uint64_t c : 10
};
foo f;
f.b = 0xab;
printf("Foo.b: %llx", f.b);
This usually gave me random garbage like Foo.b:7fa0000000ab (always with the
correct value at the end). It seems to me that the f.b is being passed as a 32
bit int on the stack but because it is declared as a uint64_t bitfield the
-Wformat check assumes that %llx is okay.
clang --version
clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
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