CompilerFlags

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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. 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.
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First enabled in Ubuntu 8.10. See [:Security/FortifySource:] for further details. Most problems are related to common unsafe uses of certain libc functions. First enabled in Ubuntu 8.10. See [:Security/FortifySource] for further details. Most problems are related to common unsafe uses of certain libc functions.
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 The call to {{{read()}}} was done into a buffer with the wrong size. Double-check the size argument and the buffer size.   The call to {{{read()}}} was done into a buffer with the wrong size. Double-check the size argument and the buffer size.

 {{{
warning: passing argument 1 of 'memcpy' discards qualifiers from pointer target type
warning: passing argument 1 of 'strcpy' discards qualifiers from pointer target type
}}}
  Code compiled with {{{-Werror}}} and using memcpy/strcpy/etc with qualifier overrides will fail. This is a bug in glibc 2.7. See [https://launchpad.net/bugs/217481].

 {{{
*** %n in writable segment detected ***
Aborted
}}}
  Use of {{{"%n"}}} in a format string is limited to read-only memory (not stack or heap allocated strings).

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. Most problems are related to packages that do not use stdlib directly (kernel modules, certain libraries, etc).

Failure example:

  • '__stack_chk_fail' symbol not found

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

-D_FORTIFY_SOURCE=2

First enabled in Ubuntu 8.10. See [:Security/FortifySource] for further details. Most problems are related to common unsafe uses of certain libc functions.

Failure examples:

  • error: ignoring return value of 'int system(const char*)', declared with attribute warn_unused_result
    • The return value from system() functions should be evaluated and handled appropriately.

    error: call to '__open_missing_mode' declared with attribute error: open with O_CREAT in second argument needs 3 arguments
    • When using open() with O_CREAT, best-practice is to define a valid mode argument.

    warning: call to ‘__read_chk_warn’ declared with attribute warning: read called with bigger length than size of the destination buffer
    • The call to read() was done into a buffer with the wrong size. Double-check the size argument and the buffer size.

    warning: passing argument 1 of 'memcpy' discards qualifiers from pointer target type
    warning: passing argument 1 of 'strcpy' discards qualifiers from pointer target type
    *** %n in writable segment detected ***
    Aborted
    • Use of "%n" in a format string is limited to read-only memory (not stack or heap allocated strings).

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

-Wformat -Wformat-security

First enabled in Ubuntu 8.10. These options should only cause build failures 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 forgot to use "%s" for a *printf function. For example:

  • fprintf(stderr,buf);

should be:

  • fprintf(stderr,"%s",buf);

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

-Wl,-z,relro

First enabled in Ubuntu 8.10. This option paves the way for using -z now to further harden long-running programs like daemons.

No known failure examples.

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

ToolChain/CompilerFlags (last edited 2021-09-02 05:51:07 by paelzer)