Commit 72d751cba9 "build: rework library bundling" introduced a new helper
binary "runas" whose sole purpose was mangling the argv vector passed to
the actual called ELF image so that the renamed executable could obtain the
proper name from argv[0].
This approach, however totally defeated the purpose of calling bundled ELF
executables through the shipped ld.so loader since the execv() invocation
performed by "runas" would cause the kernel the interprete the final program
image through the system ELF loader again.
To solve the problem, use an alternative approach of shipping a shared object
"runas.so" which uses an ELF ".init_array" function pointer to obtain the
argv[] vector of the to-be-executed main() function and mangle it in-place.
The actual argv[0] value to use is communicated out-of-band using an
environment variable "RUNAS_ARG0" by the shell wrapper script. The wrapper
script also takes care of setting LD_PRELOAD to instruct the shipped ELF
loader to preload the actual ELF program image with the "runas.so" helper
library.
Fixes FS#909.
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
Rework the bundle-libraries.sh implementation to use a more robust approach
for executing host binaries through the shipped ELF loader and libraries.
The previous approach relied on symlinks pointing to a wrapper script which
caused various issues, especially with multicall binaries as the original
argv[0] name was not preserved through the ld.so invocation. Another down-
side was the fact that the actual binaries got moved into another directory
which caused executables to fail looking up resources with paths relative
to the executable location.
The new library wrapper implements the following improvements:
- Instead of symlinks pointing to a common wrapper, each ELF executable
is now replaced by a unqiue shell script which retains the original
program name getting called
- Instead of letting ld.so invoke the ELF executable directly, launch
the final ELF binary through a helper program which fixes up the argv[0]
argument for the target program
- Support sharing a common location for the bundled libraries instead of
having one copy in each directory containing wrapped binaries
Finally modify the SDK build to wrap the staging_dir and toolchain binaries
which allows to use the SDK on systems with a different glibc version.
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
