CompilerFlags

Revision 1 as of 2008-05-02 21:18:34

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This page documents the Ubuntu-specific default compiler flags in the toolchain. Based on the work from GccSsp, [:Security/HardeningWrapper:], and DistCompiler. Please attempt to fix a source package's problems before disabling a given compiler feature.

-fstack-protector

First enabled in Ubuntu 6.10. See GccSsp for further details.

Failure example: 

'__stack_chk_fail' symbol not found

Disabled with -fno-stack-protector or -nostdlib.

-D_FORTIFY_SOURCE=2

First enabled in Ubuntu 8.10. See [:Security/FortifySource:] for more details.

Failure examples: 

  • error: ignoring return value of 'int system(const char*)', declared with attribute warn_unused_result
    error: call to '__open_missing_mode' declared with attribute error: open with O_CREAT in second argument needs 3 arguments
    warning: call to ‘__read_chk_warn’ declared with attribute warning: read called with bigger length than size of the destination buffer

Reduced checking via -D_FORTIFY_SOURCE=1. Disabled with -U_FORTIFY_SOURCE or -D_FORTIFY_SOURCE=0.

-Wformat -Wformat-security

First enabled in Ubuntu 8.10. These options should only cause FTBFS if the package is compiling with -Werror.

Failure examples: 

  • warning: format not a string literal and no format arguments

This is caused by code that fails to use "%s" for a *printf function. For example: 

printf(buf);

should be: 

printf("%s",buf);

Disabled with -Wno-format-security or -Wformat=0.

-Wl,-z,relro

First enabled in Ubuntu 8.10.

No known failure examples.

Disabled with -Wl,-z,norelro in LDFLAGS.