- This will invoke the `./configure` with arguments (such as

- `--prefix=/usr`) to adjust the paths to the packaging defaults.

- Prior to that, some common problems in autotools scripts are

- automatically patched across the source tree.

- so they can be used by makefiles and other build tools.  (However,

- early in the `%build` section.  (Again, existing environment variables

-   `CFLAGS` variable).  Also historically available as `%{optflags}`.

-   `LDFLAGS`.  Note that the contents quotes linker arguments using

-   driver.  At the start of the `%build` section, the environment

- script (v2.4.6+) from hardcoding %_libdir into the binaries' RPATH.

-    %define _lto_cflags %{nil}

- can use the %_build_id_flags macro:

-     %define _strict_symbol_defs_build 1

-     %define _legacy_common_support 1

- * `-O2`: Turn on various GCC optimizations.  See the [GCC manual](https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html#index-O2).

- * `-g`: Generate debugging information (DWARF).  In Fedora, this data

-   This can occasionally result in compilation errors.  In this case,

- *   `-fPIE`: Compile for a position-independent executable (PIE),

-     enabling full address space layout randomization (ASLR).  This is

-     similar to `-fPIC`, but avoids run-time indirections on certain

-     architectures, resulting in improved performance and slightly

-     smaller executables.  However, compared to position-dependent code

-     (the default generated by GCC), there is still a measurable

-     performance impact.

-     If the command line also contains `-r` (producing a relocatable

-     object file), `-fpic` or `-fPIC`, this flag is automatically

-     dropped.  (`-fPIE` can only be used for code which is linked into

-     the main program.) Code which goes into static libraries should be

-     compiled with `-fPIE`, except when this code is expected to be

-     linked into DSOs, when `-fPIC` must be used.

-     To be effective, `-fPIE` must be used with the `-pie` linker flag

-     when producing an executable, see below.

- *   `-fcf-protection`: Instrument binaries to guard against

-     ROP/JOP attacks.  Used on i686 and x86_64.

- *   `-mbranch-protection=standard`: Instrument binaries to guard against

-      ROP/JOP attacks.  Used on aarch64.

- *   `-m64` and `-m32`: Some GCC builds support both 32-bit and 64-bit in

-     the same compilation.  For such architectures, the RPM build process

-     explicitly selects the architecture variant by passing this compiler

-     flag.

- *   **armhfp**: `-march=armv7-a -mfpu=vfpv3-d16  -mfloat-abi=hard`

-     selects an Arm subarchitecture based on the ARMv7-A architecture

-     with 16 64-bit floating point registers.  `-mtune=cortex-8a` selects

-     tuning for the Cortex-A8 implementation (while preserving compatibility

-     with other ARMv7-A implementations).  `-mabi=aapcs-linux` switches to

-     the AAPCS ABI for GNU/Linux.

- *   **i686**: `-march=i686` is used to select a minmum support CPU level

-     of i686 (corresponding to the Pentium Pro).  SSE2 support is

-     enabled with `-msse2` (so only CPUs with SSE2 support can run the

-     compiled code; SSE2 was introduced first with the Pentium 4).

-     `-mtune=generic` activates tuning for a current blend of CPUs

-     (under the assumption that most users of i686 packages obtain them

-     through an x86_64 installation on current hardware).

-     `-mfpmath=sse` instructs GCC to use the SSE2 unit for floating

-     point math to avoid excess precision issues.  `-mstackrealign`

-     avoids relying on the stack alignment guaranteed by the current

-     version of the i386 ABI.

- *   **ppc64le**: `-mcpu=power8 -mtune=power8` selects a minimum supported

-     CPU level of POWER8 (the first CPU with ppc64le support) and tunes

-     for POWER8.

- *   **s390x**: `-march=zEC12 -mtune=z13` specifies a minimum supported CPU

-     level of zEC12, while optimizing for a subsequent CPU generation

-     (z13).

- *   **x86_64**: `-mtune=generic` selects tuning which is expected to

-      beneficial for a broad range of current CPUs.

- *   **aarch64** does not have any architecture-specific tuning.

- default_cflags=`rpm -E %{build_cflags}`

- default_cxxflags=`rpm -E %{build_cxxflags}`

- default_ldflags=`rpm -E %{build_ldflags}`

- cflags=`rpm -D '%toolchain gcc' -E %{build_cflags}`

- cxxflags=`rpm -D '%toolchain gcc' -E %{build_cxxflags}`

- ldflags=`rpm -D '%toolchain gcc' -E %{build_ldflags}`