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Merge pull request #63 from Logarithmus/readme-gcc-guide

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README.md: add guide to using mold with GCC via -B option
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Rui Ueyama 2021-07-01 09:38:34 +09:00 committed by GitHub
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@ -84,10 +84,15 @@ $ sudo apt-get install dwarfdump libc6-dev:i386 lib32gcc-10-dev gcc-multilib
On Unix, the linker command (which is usually `/usr/bin/ld`) is On Unix, the linker command (which is usually `/usr/bin/ld`) is
invoked indirectly by `cc` (or `gcc` or `clang`), which is typically invoked indirectly by `cc` (or `gcc` or `clang`), which is typically
in turn indirectly invoked by `make` or some other build system in turn indirectly invoked by `make` or some other build system command.
command. It is sometimes very hard to pass an appropriate command line
option to `cc` to specify an alternative linker.
A classic way to use `mold`:
- `clang` before 12.0: pass `-fuse-ld=<absolute-path-to-mold-executable>`;
- clang after 12.0: pass `--ld-path=<absolute-path-to-mold-executable>`;
- gcc: `--ld-path` patch [has been declined by GCC maintainers](https://gcc.gnu.org/pipermail/gcc-patches/2021-June/573833.html), instead they advise to use a [workaround](https://gcc.gnu.org/pipermail/gcc-patches/2021-June/573823.html): create directory `<dirname>`, then `ln -s <path-to-mold> <dirname>/ld`, and then pass `-B<dirname>` (`-B` tells GCC to look for `ld` in specified location).
It is sometimes very hard to pass an appropriate command line
option to `cc` to specify an alternative linker.
To deal with the situation, mold has a feature to intercept all To deal with the situation, mold has a feature to intercept all
invocations of `/usr/bin/ld`, `/usr/bin/ld.lld` or `/usr/bin/ld.gold` invocations of `/usr/bin/ld`, `/usr/bin/ld.lld` or `/usr/bin/ld.gold`
and redirect it to itself. To use the feature, run `make` (or other and redirect it to itself. To use the feature, run `make` (or other
@ -103,10 +108,6 @@ file intercepts all function calls to exec-family functions to replace
`argv[0]` with `mold` if it is `/usr/bin/ld`, `/usr/bin/ld.gold` or `argv[0]` with `mold` if it is `/usr/bin/ld`, `/usr/bin/ld.gold` or
`/usr/bin/ld.lld`. `/usr/bin/ld.lld`.
Alternatively, you can pass `-fuse-ld=<absolute-path-to-mold-executable>`
to a linker command line. Since GCC doesn't support that option,
I recommend using clang.
mold leaves its identification string in `.comment` section in an output mold leaves its identification string in `.comment` section in an output
file. You can print it out to verify that you are actually using mold. file. You can print it out to verify that you are actually using mold.