Arch Linux

Most of the installed binaries in an Arch GCC build are not compiled with preferred CFLAGS / LDFLAGS (from makepkg.conf). The reason is due to a combination of factors:

1. Arch uses the default Makefile target which performs a 3-stage bootstrap (3rd stage is what gets installed)
2. Arch doesn't employ the documented[1] BOOT_CFLAGS var, or the badly documented BOOT_LDFLAGS var.

Essentially, to pass preferred FLAGS passed down into the 2nd and 3rd stages of the bootstrap, one has to utilise BOOT_*FLAGS vars. This is what other distros do e.g: Fedora[2] and Debian[3]. (Sidenote: those links demonstrate why most of us appreciate the utter simplicity of PKGBUILDs :)

Now, just to complicate matters there are also *FLAGS_FOR_TARGET vars which affect how the target libraries get built.

In oversimplified terms the payload of a GCC build comprises of:

- compilers (gcc, g++, cpp, cc1, etc.)
- target libs (libgcc, libstdc++, and friends)

In the current Arch GCC build, CFLAGS are carried through to CFLAGS_FOR_TARGET. LDFLAGS are mostly lost (I say mostly because they do get used in certain less important parts of the build). BOOT_*FLAGS just get the defaults.

The upshot of all this means the status quo is as follows (using current distro FLAGS from devtools):

compilers:
BOOT_CFLAGS="-g -O2"
BOOT_LDFLAGS=""

target libs:
CFLAGS_FOR_TARGET="-g -march=x86-64 -mtune=generic -O2 -fno-plt"
(-g is added by GCC configury, -pipe is filtered out in PKGBUILD)
LDFLAGS_FOR_TARGET=""

This came to light while looking into ways to improve the bootstrap of the full Arch toolchain (see  FS#70954 ). Interestingly, if you build GCC with `--disable-bootstrap', the compilers *are* built with preferred CFLAGS / LDFLAGS but the target libs are the same. Also, I will note here it is possible to prove that a non-bootstrapped GCC can produce identical binaries to a bootstrapped one (I should post a separate write-up of this somewhere because it's a bit tricky).

Recommendations:
- build GCC with `make -O' (as per  FS#70871 ) in order to produce comprehensible log files
- add BOOT_CFLAGS, BOOT_LDFLAGS and LDFLAGS_FOR_TARGET to the make invocation
- while we're at it may as well add STAGE1_CFLAGS as per  FS#71476 

make -O STAGE1_CFLAGS="-O2" \
BOOT_CFLAGS="$CFLAGS" \
BOOT_LDFLAGS="$LDFLAGS" \
LDFLAGS_FOR_TARGET="$LDFLAGS"

I've tested this in a full toolchain bootstrap using latest binutils-2.37, gcc-11.2 and glibc-2.34. The GCC testsuite results are identical as compared to when not building like above. The target libs are all now full RELRO (except for libgcc_s.so.1 but this has now been fixed on GCC trunk[4]). Overall there are less complaints from namcap.

NOTE: If / when Arch changes the distro defaults in devtools to match current pacman makepkg.conf, certain CFLAGS will need to be filtered out. This is exacly what the Fedora rpm specfile does.

[1] https://gcc.gnu.org/install/build.html
[2] https://src.fedoraproject.org/rpms/gcc/blob/rawhide/f/gcc.spec
[3] https://salsa.debian.org/toolchain-team/gcc/-/blob/master/debian/rules2
[4] https://gcc.gnu.org/pipermail/gcc-patches/2021-August/576785.html