Compact relocations are not supported #24218
Description
Environment
Sun May 18 06:23:36 AM UTC 2025
radare2 5.9.8 0 @ linux-x86-64
birth: git.5.9.8 2025-03-15__02:06:40
options: gpl release -O1 cs:5 cl:2 meson
Linux x86_64Description
There is a new (experimental) relocation format in Clang now called "compact relocations" (or "crel" for short): https://maskray.me/blog/2024-03-09-a-compact-relocation-format-for-elf
r2 doesn't understand crel, and gets confused if you give it a crel-enabled file.
crel is currently experimental, which probably means it could change before it is released. This is what happens if you try to enable crel without the experimental flag:
$ clang -Wa,--crel -o test.o test.c -c
clang: error: -Wa,--allow-experimental-crel must be specified to use -Wa,--crel. CREL is experimental and uses a non-standard section type code
Since it's experimental, it would be understandable if r2 decided not to support it for now. On the other hand, there could be binaries floating around that use it, so it could be valuable to support it even in its experimental state.
Test
$ cat test.c
int callee(void);
int caller(void) { return callee(); }
$ clang -Wa,--crel -o test.o test.c -c -Wa,--allow-experimental-crel
$ r2 -A -e bin.cache=true -c 's sym.caller; pdf' test.o
INFO: Analyze all flags starting with sym. and entry0 (aa)
INFO: Analyze imports (af@@@i)
INFO: Analyze symbols (af@@@s)
INFO: Analyze all functions arguments/locals (afva@@@F)
INFO: Analyze function calls (aac)
INFO: Analyze len bytes of instructions for references (aar)
ERROR: invalid memory at 0x08000125
INFO: Finding and parsing C++ vtables (avrr)
INFO: Analyzing methods (af @@ method.*)
INFO: Recovering local variables (afva@@@F)
INFO: Type matching analysis for all functions (aaft)
INFO: Propagate noreturn information (aanr)
INFO: Use -AA or aaaa to perform additional experimental analysis
;-- section..text:
;-- rip:
┌ 11: sym.caller ();
│ 0x08000040 55 push rbp ; [02] -r-x section size 11 named .text
│ 0x08000041 4889e5 mov rbp, rsp
│ 0x08000044 e800000000 call 0x8000049
│ ; CALL XREF from sym.caller @ 0x8000044(x)
│ 0x08000049 5d pop rbp
└ 0x0800004a c3 ret
Note how the call instruction above is not resolved symbolically, as it would be normally:
$ clang -o test.o test.c -c
$ r2 -A -e bin.cache=true -c 's sym.caller; pdf' test.o
INFO: Analyze all flags starting with sym. and entry0 (aa)
INFO: Analyze imports (af@@@i)
INFO: Analyze symbols (af@@@s)
INFO: Analyze all functions arguments/locals (afva@@@F)
INFO: Analyze function calls (aac)
INFO: Analyze len bytes of instructions for references (aar)
ERROR: invalid memory at 0x08000138
INFO: Finding and parsing C++ vtables (avrr)
INFO: Analyzing methods (af @@ method.*)
INFO: Recovering local variables (afva@@@F)
INFO: Type matching analysis for all functions (aaft)
INFO: Propagate noreturn information (aanr)
INFO: Use -AA or aaaa to perform additional experimental analysis
;-- section..text:
;-- rip:
┌ 11: sym.caller ();
│ 0x08000040 55 push rbp ; RELOC 32 .text @ 0x08000040 - 0x8000090 ; [02] -r-x section size 11 named .text
│ 0x08000041 4889e5 mov rbp, rsp
│ 0x08000044 e86f010000 call callee
│ 0x08000049 5d pop rbp
└ 0x0800004a c3 ret