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Makefile

Build:

mkdir glibc
cd glibc
git clone git://sourceware.org/git/glibc.git src
cd src
git checkout glibc-2.21
cd ..
mkdir build
cd build
# TODO better way? Why is this needed?
unset LD_LIBRARY_PATH
GLIBC_INSTALL_DIR="$(pwd)/../install"
../src/configure --prefix="$GLIBC_INSTALL_DIR"
time make -j5
time make install

Took 4 minutes on a 2012 machine for version 2.21.

Hack and try it out:

cd ../src

cat <<'EOS' | git apply -
diff --git a/libio/ioputs.c b/libio/ioputs.c
index 39b4bb7..575bb30 100644
--- a/libio/ioputs.c
+++ b/libio/ioputs.c
@@ -51,0 +52,2 @@ weak_alias (_IO_puts, puts)
+  _IO_sputn (_IO_stdout, "hacked\n", 7);
+
diff --git a/stdlib/stdlib.h b/stdlib/stdlib.h
index 0134378..5d64442 100644
--- a/stdlib/stdlib.h
+++ b/stdlib/stdlib.h
@@ -134,0 +135,2 @@ __END_NAMESPACE_C99
+#undef EXIT_SUCCESS
+#define EXIT_SUCCESS 101
EOS

make -j5
make install

cd /tmp
echo '
#include <stdio.h>
#include <stdlib.h>

int main() {
    puts("hello world");
    return EXIT_SUCCESS;
}
' > main.c

# TODO confirm.
gcc -v -nostdinc -I"$GLIBC_INSTALL_DIR/include" \
  -I'/usr/lib/gcc/x86_64-linux-gnu/4.8/include' \
  -nostartfiles \
  -nodefaultlibs -L"$GLIBC_INSTALL_DIR/lib" \
  -Wl,-rpath="$GLIBC_INSTALL_DIR/lib" \
  "$GLIBC_INSTALL_DIR/lib/crt1.o" \
  "$GLIBC_INSTALL_DIR/lib/crti.o" \
  "$GLIBC_INSTALL_DIR/lib/crtn.o" \
  "$(gcc --print-file-name=crtbegin.o)" \
  "$(gcc --print-file-name=crtend.o)" \
  main.c \
  -lgcc -lc -lgcc -lc

./a.out
echo $?

Output:

hello world
hacked
101

Using the built stdlib

Not easy.

The best thing to do is likely run gcc -v and extract the mandatory commands, while adapting paths to your compiled library.

Things to consider:

  • first disable defaults, then include things, e.g.:

    • -nostartfiles followed by the crt files
    • -nostdinc followed by -I
    • -nostdinc followed by -I

  • -I'/usr/lib/gcc/x86_64-linux-gnu/4.8/include' is required by GCC provided headers. I could not get that path programmatically from GCC as I managed for crtbegin.o with --print-file-name.

  • -nodefaultlibs -L"$GLIBC_INSTALL_DIR/lib" for the

  • -Wl,-rpath="$GLIBC_INSTALL_DIR/lib" so that ldd will be able to find your custom directory when loading

  • -lgcc -lc -lgcc -lc twice to resolve interdependencies

Another strategy is to call the smaller programs cpp, gcc -c, ld individually with the paths.

LD_LIBRARY_PATH during compilation

Make sure that LD_LIBRARY_PATH does not contain the current directory, or else when you cd into the build directory, things your executables are going to break.

In particular, trailing and leading colons : like :/some/path imply the current directory!

Interesting installed files

  • /bin/ldd