README - dependency list is incomplete: `make sim` and `make build-isa-tests` both fail on a clean Ubuntu 24.04 following it exactly

[badnikhil]

Following README.md (Section - 1)exactly on a clean Ubuntu 24.04.1 machine, neither make sim nor
make build-isa-tests completes. Two separate gaps in the dependency list, both reproducible.

Environment: Ubuntu 24.04.1, gcc/g++ 13.3.0, Verilator 5.020, core_tile at 2528e7d (v3.1.0),
submodules initialised recursively.

1. libboost-system-dev is required but not listed make sim cannot complete

README.md:25 lists Boost as only libboost-regex-dev >= 1.53. make sim depends on libdisasm
(simulator/verilator/verilator.mk:36), which configures Spike (simulator/reference/spike.mk:5-7),
and that configure step aborts:

checking for boostlib >= 1.53 (105300)... yes
checking whether the Boost::ASIO library is available... yes
configure: error: Could not find a version of the Boost::Asio library!
make: *** [simulator/reference/spike.mk:7: simulator/reference/build/Makefile] Error 1

The two adjacent lines contradict each other, which sends people looking for an Asio problem. The
actual cause is libboost_system:

• simulator/reference/riscv-isa-sim/ax_boost_base.m4:154-163 - with no --with-boost, the macro
  scans /usr /usr/local /opt /opt/local and sets BOOST_LDFLAGS=-L/usr/lib/x86_64-linux-gnu on
  Ubuntu.
• ax_boost_asio.m4:65-68 is the check that prints yes. It is an AC_COMPILE_IFELSE on
  #include <boost/asio.hpp> - compile only, no link - so it succeeds with no library present,
  because Asio is header-only.
• Inside that branch, ax_boost_asio.m4:84 sets BN=boost_system, and :87 globs
  $BOOSTLIBDIR/libboost_system*.so*.
• With no libboost_system present the glob is empty, $ax_lib stays unset, and :99-100 raises
  the error above.

libboost-regex-dev does not pull in libboost-system. On Ubuntu 24.04 the README's exact list
resolves to a closure with no libboost-system in it:

$ apt-get install --no-install-recommends -s gcc gcc-riscv64-unknown-elf \
      device-tree-compiler libboost-regex-dev verilator | grep '^Inst ' | grep -i boost
libboost-iostreams1.83.0
libboost-thread1.83.0
libboost-locale1.83.0
libboost1.83-dev
libboost-regex1.83.0
libboost-regex1.83-dev
libboost-regex-dev

Adding libboost-system-dev makes make sim succeed (verified: ./sim, 27 MB, and the ISA suite
runs clean - 169 passed / 0 failed via tb/tb_isa_tests/run-tests.py).

This is related to #12 but not the same failure. That report got as far as
checking for main in -lboost_system... yes and then died at
configure: error: Could not link against boost_system ! - ax_boost_asio.m4:102-103, a link
failure on a machine where the library was present. The failure above is the earlier
:99-100 branch, reached when the library is absent, which is what following README.md:25
produces. #12 was answered with libboost-all-dev in the thread, which is the same fix; recording it
in the README as well would mean the next person does not have to find the thread.

Two smaller items in the same path:

• python3 and perl are also required but unlisted. simulator/bootrom/bin2hex.py builds
  bootrom.hex, tb/tb_isa_tests/run-tests.py runs the suite, and Verilator's driver is a Perl
  script.
• simulator/reference/spike.mk:7 invokes ../riscv-isa-sim/configure with no arguments and no
  variable hook, so a Boost outside the default prefixes cannot be accommodated without editing the
  makefile. A SPIKE_CONFIGURE_ARGS ?= appended to that line would cover it.

2. The riscv64-unknown-elf-gcc requirement is understated - make build-isa-tests fails

README.md:23 asks for riscv64-unknown-elf-gcc >= 12.0. Ubuntu's gcc-riscv64-unknown-elf
package is 13.2.0, so it satisfies that literally, but it ships no C library, and
make build-isa-tests stops at:

riscv-tests/isa/../env/v/string.c:1:10: fatal error: string.h: No such file or directory

The default target include path contains only the two GCC-internal directories - no libc anywhere:

$ riscv64-unknown-elf-gcc -march=rv64g -mabi=lp64d -E -Wp,-v -x c /dev/null
#include <...> search starts here:
 .../lib/gcc/riscv64-unknown-elf/13.2.0/include
 .../lib/gcc/riscv64-unknown-elf/13.2.0/include-fixed
End of search list.

Installing picolibc-riscv64-unknown-elf does not resolve it either: its headers land in
/usr/lib/picolibc/riscv64-unknown-elf/include, which is not on that path, and there is no spec
file for the target (fatal error: cannot read spec file 'picolibc.specs').

Scope is limited: only the -v- (virtual-memory) tests and the benchmarks need a libc. All 185
rv64 -p- tests build and run with -nostdlib -nostartfiles, which is enough to exercise the core.
Building them directly against riscv-tests/isa/Makefile works:

make -k -j8 -f $ISA_SRC/Makefile src_dir=$ISA_SRC XLEN=64 \
  RISCV_GCC_OPTS="-static -mcmodel=medany -fvisibility=hidden -nostdlib -nostartfiles" \
  <rv64*-p-* targets>

→ 185 binaries. run-tests.py then attempts 170 of them (its glob is limited to
IMPLEMENTED_EXTENSIONS, so rv64uzfh, rv64uzbc and rv64uc are built but never selected) and
reports 169 passed / 0 failed.

Suggested fix

In README.md Section-1:

• add libboost-system-dev to the list at line 25 (or replace the entry with libboost-all-dev,
  which is what +vcd writes an FST file named dump_file.vcd, ignores the documented =path argument, and the documented default filename does not match the code #12 was told to install);
• add python3 and perl;
• state at line 23 that a newlib toolchain is needed for the full test set
  (riscv-gnu-toolchain, xPack or a SiFive prebuilt), and note that a distribution
  gcc-riscv64-unknown-elf covers the -p- tests only.

Optionally, a make target that builds just the rv64 -p- tests would give newcomers a working
suite from distribution packages alone.