[Bug driver/111527] New: COLLECT_GCC_OPTIONS option hits single-variable limits too early

["slyfox at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111527

            Bug ID: 111527
           Summary: COLLECT_GCC_OPTIONS option hits single-variable limits
                    too early
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: driver
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at gcc dot gnu.org
  Target Milestone: ---

Tl;DR:

  linux allows you to pass up to 2MB of command line arguments to the tools
limiting each individual option to 128KB. Unfortunately `gcc` collects all the
options into a single `COLLECT_GCC_OPTIONS` variable and hits the smaller 128KB
limit.

  This causes periodic problems for distributions that install each individual
package into a separate directory. One of them is `NixOS`.

  Could `gcc` be amended not to use single limiting `COLLECT_GCC_OPTIONS`
variable and use, say, direct arguments to pass options around? Or even use
response file if it hits `-E2BIG`?

  Fake reproducer: 2 huge variables that programs normally accept, but not
`gcc`:

  $ big_100k_var=$(printf "%0*d" 100000 0)

  # this works: 200KB of options for `printf` external command
  $ $(which printf) "%s %s" $big_100k_var $big_100k_var >/dev/null; echo $?
  0

  # this fails: 200KB of options for `gcc`, fails in `cc1`
  $ touch a.c; gcc -c a.c -DA=$big_100k_var -DB=$big_100k_var
  gcc: fatal error: cannot execute 'cc1': execv: Argument list too long
  compilation terminated.

  Thanks!

MOre words

In `nixpkgs` repository each package gets installed into it's own unique
directory:

    /nix/store/hash1-foo/include/foo.h
    /nix/store/hash2-bar/include/bar.h
    ...

If any of those encounter `__FILE__` macros in static inline functions they
usually embed full path to header files into final binaries as is.

I wanted to remap all those paths into form that does not contain hashes:

   
-fmacro-prefix-map=/nix/store/hash1-foo/include/foo.h=/nix/store/00000000-foo/include/foo.h
   
-fmacro-prefix-map=/nix/store/hash2-bar/include/bar.h=/nix/store/00000000-bar/include/bar.h
    ...

When I got to packages that use about ~100 include directories I started
getting  errors from `cc1`:

```
Command line: `gcc -m64 -mcx16 $remap_options
/build/qemu-8.1.0/build/meson-private/tmpbyikv8nc/testfile.c \
  -o /build/qemu-8.1.0/build/meson-private/tmpbyikv8nc/output.exe
-D_FILE_OFFSET_BITS=64 \
  -O0 -Wl,--start-group -laio -Wl,--end-group -Wl,--allow-shlib-undefined` -> 1
stderr:
gcc: fatal error: cannot execute 'cc1': execv: Argument list too long
compilation terminated.
```

The limit felt too low and I found the `COLLECT_GCC_OPTIONS` variable.