porocyon / smol Goto Github PK

Currently using readelf to find symbols, which can't properly parse LTO objects. Use something that does instead? (nm?)

Is this even possible? Relocation types need to be known by smolemit.py...

Users not doing this correctly will be faced by cryptic segfaults.

A warning (or error) should be shown if the following is not true:

• There is exactly one .text.startup._start or .text._start section (can't have both, can't have none)
• The _start symbol must be at the very beginning of the above section.

I hit a segfault issue trying to change up my build process a bit.

Long story short, I've narrowed the problem down to the first function call to anything linked from outside the main obj file. In this case, moving my function from the same file as main() to a different .o introduces a segfault on the call instruction and the calculated address looks wrong to me, but that's where my knowledge runs dry. it seems like the address of all the call instructions are off by a few bytes but I could be misreading or misinterpreting GDB output.

Relevant, my debugging symbols are borked per #14 and the stack trace is frankly dizzying without them.

If you give me a hint I can probably figure out the fix and PR it, I've been using this thing a bit and I want to better understand it, would enjoy contributing.

python3 ./smold.py --debugout "bin/hello-crt.dbg" --smolrt "./rt" --smolld "./ld" -falign-stack -fuse-interp -fifunc-support --verbose  --ldflags=-Wl,-Map=bin/hello-crt.map -lSDL2 -lX11 -lm -lc  "obj/hello.lto.o" obj/crt1.lto.o "bin/hello-crt"
arch: x86_64
cc: ['/usr/bin/cc', '-m64', '-nostartfiles', '-nostdlib', '-r', '-flinker-output=nolto-rel', '-o', '/tmp/smolinch82g1jp.o', 'obj/hello.lto.o', 'obj/crt1.lto.o']
libs = ['/usr/lib/libSDL2.so', '/usr/lib/libX11.so.6', '/usr/lib/libm.so.6', '/usr/lib/libc.so.6']
  File "./smold.py", line 216, in <module>
    rv = main()
  File "./smold.py", line 188, in main
    error("E: the symbol '" + symbol + "' is provided by more than one library: " + str(libs_for_symbol))
  File "./smol/shared.py", line 70, in error
    traceback.print_stack()
E: the symbol 'printf' is provided by more than one library: ['libc.so.6', 'libc.so.6']

See 4601003 , cf. #4 and #9

EDIT: this is present in 405d8eb as well, rolling back master for now

Probably just needs some boilerplate in the linker script

Should be doable using readelf or sth I think?

Recently ran into a problem with segfaults (separate issue incoming... 😁 ) and discovered that the --debugout flag causes my ld to break and complain about a discarded .got.plt section. Worth noting these .o files are products of Rust. I managed to get it to link by removing the catch-all DISCARD in the linker script but then none of the debug symbols lined up.

I can provide objdumps or whatever of the two .o files and the /tmp/ stuff, just let me know what you'd want

'Dynamically' adapt this check on whether there are symbols with a zero LSB, zero low word, etc. etc., so that the smallest code size can still be achieved.

make all fails on ubuntu 18.04

cc -flto -Wall -Wextra -Wpedantic -std=gnu11 -nostartfiles -fno-PIC -Os -fno-plt -fno-stack-protector -fno-stack-check -fno-unwind-tables -fno-asynchronous-unwind-tables -fomit-frame-pointer -ffast-math -no-pie -fno-pic -fno-PIE -m64 -march=core2 -ffunction-sections -fdata-sections -fno-plt -m64 -D_REENTRANT -I/usr/include/SDL2 -c "test/hello.c" -o "obj/hello.lto.o"
cc -flto -Wall -Wextra -Wpedantic -std=gnu11 -nostartfiles -fno-PIC -Os -fno-plt -fno-stack-protector -fno-stack-check -fno-unwind-tables -fno-asynchronous-unwind-tables -fomit-frame-pointer -ffast-math -no-pie -fno-pic -fno-PIE -m64 -march=core2 -ffunction-sections -fdata-sections -fno-plt -m64 -D_REENTRANT -I/usr/include/SDL2 -c "rt/crt1.c" -o "obj/crt1.lto.o"
rt/crt1.c:22:1: warning: 'naked' attribute directive ignored [-Wattributes]
) {
^
cc -m64 -nostartfiles -nostdlib -r -o "obj/hello.start.o" obj/hello.lto.o obj/crt1.lto.o
python3 src/smol.py -lc -lSDL2 -lX11 "obj/hello.start.o" "obj/symbols.hello.start.asm"
Traceback (most recent call last):
File "src/smol.py", line 77, in
main()
File "src/smol.py", line 67, in main
library = find_symbol(args.scanelf, libs, libnames, symbol)
File "/home/martin/work/demos/Clutter-1k/smol/src/smolparse.py", line 127, in find_symbol
'+{}'.format(symbol)] + libraries, stderr=subprocess.DEVNULL)
File "/usr/lib/python3.6/subprocess.py", line 356, in check_output
**kwargs).stdout
File "/usr/lib/python3.6/subprocess.py", line 423, in run
with Popen(*popenargs, **kwargs) as process:
File "/usr/lib/python3.6/subprocess.py", line 729, in init
restore_signals, start_new_session)
File "/usr/lib/python3.6/subprocess.py", line 1278, in _execute_child
executable = os.fsencode(executable)
File "/usr/lib/python3.6/os.py", line 800, in fsencode
filename = fspath(filename) # Does type-checking of filename.
TypeError: expected str, bytes or os.PathLike object, not NoneType
Makefile:83: recipe for target 'obj/symbols.hello.start.asm' failed
make: *** [obj/symbols.hello.start.asm] Error 1

Sorting needs to happen so that the libraries that declare the Real™ versions of the symbols get checked before those that export a weak version of that symbol, so that -fskip-zero-value (hopefully) won't be needed.