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update README once more

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PoroCYon 2020-08-24 20:47:44 +02:00
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README.md
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@ -18,13 +18,14 @@ PoC by Shiz, bugfixing and 64-bit version by PoroCYon.
the smol startup/symbol resolving code will jump to an undefined location. the smol startup/symbol resolving code will jump to an undefined location.
```sh ```sh
./smold.py -fuse-interp -falign-stack [--opts...] -lfoo -lbar input.o... output.elf # example:
./smold.py -fuse-dnload-loader [--opts...] -lfoo -lbar input.o... output.elf
``` ```
``` ```
usage: smold.py [-h] [-m TARGET] [-l LIB] [-L DIR] [-s] [-n] [-d] [-fuse-interp] [-falign-stack] [-fuse-nx] [-fuse-dnload-loader] [-fskip-zero-value] [-fuse-dt-debug] [-fuse-dl-fini] [-fskip-entries] [-fno-start-arg] [-funsafe-dynamic] usage: smold.py [-h] [-m TARGET] [-l LIB] [-L DIR] [-s] [-c] [-n] [-d] [-fno-use-interp] [-fno-align-stack] [-fuse-nx] [-fuse-dnload-loader] [-fno-skip-zero-value] [-fuse-dt-debug] [-fuse-dl-fini] [-fskip-entries] [-fno-start-arg]
[-fifunc-support] [-fifunc-strict-cconv] [--nasm NASM] [--cc CC] [--readelf READELF] [-Wc CFLAGS] [-Wa ASFLAGS] [-Wl LDFLAGS] [--smolrt SMOLRT] [--smolld SMOLLD] [--gen-rt-only] [--verbose] [--keeptmp] [-funsafe-dynamic] [-fno-ifunc-support] [-fifunc-strict-cconv] [--nasm NASM] [--cc CC] [--readelf READELF] [-Wc CFLAGS] [-Wa ASFLAGS] [-Wl LDFLAGS] [--smolrt SMOLRT] [--smolld SMOLLD] [--gen-rt-only] [--verbose]
[--debugout DEBUGOUT] [--keeptmp] [--debugout DEBUGOUT]
input [input ...] output input [input ...] output
positional arguments: positional arguments:
@ -38,16 +39,17 @@ optional arguments:
-l LIB, --library LIB -l LIB, --library LIB
libraries to link against libraries to link against
-L DIR, --libdir DIR directories to search libraries in -L DIR, --libdir DIR directories to search libraries in
-s, --hash16 Use 16-bit (BSD) hashes instead of 32-bit djb2 hashes. Implies -fuse-dnload-loader -s, --hash16 Use 16-bit (BSD2) hashes instead of 32-bit djb2 hashes. Implies -fuse-dnload-loader. Only usable for 32-bit output.
-c, --crc32c Use Intel's crc32 intrinsic for hashing. Implies -fuse-dnload-loader. Conflicts with `--hash16'.
-n, --nx Use NX (i.e. don't use RWE pages). Costs the size of one phdr, plus some extra bytes on i386. -n, --nx Use NX (i.e. don't use RWE pages). Costs the size of one phdr, plus some extra bytes on i386.
-d, --det Make the order of imports deterministic (default: just use whatever binutils throws at us) -d, --det Make the order of imports deterministic (default: just use whatever binutils throws at us)
-fuse-interp Include a program interpreter header (PT_INTERP). If not enabled, ld.so has to be invoked manually by the end user. -fno-use-interp Don't include a program interpreter header (PT_INTERP). If not enabled, ld.so has to be invoked manually by the end user.
-falign-stack Align the stack before running user code (_start). If not enabled, this has to be done manually. Costs 1 byte. -fno-align-stack Don't align the stack before running user code (_start). If not enabled, this has to be done manually. Frees 1 byte.
-fuse-nx Don't use one big RWE segment, but use separate RW and RE ones. Use this to keep strict kernels (PaX/grsec) happy. Costs at least the size of one program header entry. -fuse-nx Don't use one big RWE segment, but use separate RW and RE ones. Use this to keep strict kernels (PaX/grsec) happy. Costs at least the size of one program header entry.
-fuse-dnload-loader Use a dnload-style loader for resolving symbols, which doesn't depend on nonstandard/undocumented ELF and ld.so features, but is slightly larger. If not enabled, a smaller custom loader is used which assumes -fuse-dnload-loader Use a dnload-style loader for resolving symbols, which doesn't depend on nonstandard/undocumented ELF and ld.so features, but is slightly larger. If not enabled, a smaller custom loader is used which assumes
glibc. glibc.
-fskip-zero-value Skip an ELF symbol with a zero address (a weak symbol) when parsing libraries at runtime. Try enabling this if you're experiencing sudden breakage. However, many libraries don't use weak symbols, so this doesn't -fno-skip-zero-value Don't skip an ELF symbol with a zero address (a weak symbol) when parsing libraries at runtime. Try enabling this if you're experiencing sudden breakage. However, many libraries don't use weak symbols, so this
often pose a problem. Costs ~5 bytes. doesn't often pose a problem. Frees ~5 bytes.
-fuse-dt-debug Use the DT_DEBUG Dyn header to access the link_map, which doesn't depend on nonstandard/undocumented ELF and ld.so features. If not enabled, the link_map is accessed using data leaked to the entrypoint by ld.so, -fuse-dt-debug Use the DT_DEBUG Dyn header to access the link_map, which doesn't depend on nonstandard/undocumented ELF and ld.so features. If not enabled, the link_map is accessed using data leaked to the entrypoint by ld.so,
which assumes glibc. Costs ~10 bytes. which assumes glibc. Costs ~10 bytes.
-fuse-dl-fini Pass _dl_fini to the user entrypoint, which should be done to properly comply with all standards, but is very often not needed at all. Costs 2 bytes. -fuse-dl-fini Pass _dl_fini to the user entrypoint, which should be done to properly comply with all standards, but is very often not needed at all. Costs 2 bytes.
@ -55,7 +57,7 @@ optional arguments:
-fno-start-arg Don't pass a pointer to argc/argv/envp to the entrypoint using the standard calling convention. This means you need to read these yourself in assembly if you want to use them! (envp is a preprequisite for X11, -fno-start-arg Don't pass a pointer to argc/argv/envp to the entrypoint using the standard calling convention. This means you need to read these yourself in assembly if you want to use them! (envp is a preprequisite for X11,
because it needs $DISPLAY.) Frees 3 bytes. because it needs $DISPLAY.) Frees 3 bytes.
-funsafe-dynamic Don't end the ELF Dyn table with a DT_NULL entry. This might cause ld.so to interpret the entire binary as the Dyn table, so only enable this if you're sure this won't break things! -funsafe-dynamic Don't end the ELF Dyn table with a DT_NULL entry. This might cause ld.so to interpret the entire binary as the Dyn table, so only enable this if you're sure this won't break things!
-fifunc-support Support linking to IFUNCs. Probably needed on x86_64, but costs ~16 bytes. Ignored on platforms without IFUNC support. -fno-ifunc-support Support linking to IFUNCs. Probably needed on x86_64, but costs ~16 bytes. Ignored on platforms without IFUNC support.
-fifunc-strict-cconv On i386, if -fifunc-support is specified, strictly follow the calling convention rules. Probably not needed, but you never know. -fifunc-strict-cconv On i386, if -fifunc-support is specified, strictly follow the calling convention rules. Probably not needed, but you never know.
--nasm NASM which nasm binary to use --nasm NASM which nasm binary to use
--cc CC which cc binary to use (MUST BE GCC!) --cc CC which cc binary to use (MUST BE GCC!)