Extended Description

Found during ongoing attempts to link the FreeBSD base system with lld.

For processing .text relocations the runtime loader temporarily maps the segment with write permission. I discovered that we have an issue in FreeBSD's runtime loader: it expects the first PT_LOAD segment to be .text, and unprotects only that one. (That issue is tracked in http://bugs.freebsd.org/207631.)

This uncovered two lld issues, however.

First, lld should set DT_TEXTREL or DF_TEXTREL if the output contains relocations in non-writable segments.

DF_TEXTREL
If this flag is not set, no relocation entry should cause a modification to a non-writable segment, as specified by the segment permissions in the program header table. If this flag is set, one or more relocation entries might request modifications to a non-writable segment, and the dynamic linker can prepare accordingly.

The real issue here though is that the relocation exists at all.

feynman% findtextrel lib/libc.so.7 | head
lib/libc.so.7: ELF object contains text relocation records:
lib/libc.so.7: off: 0x9d0ac, func: __sys_numa_setaffinity
lib/libc.so.7: off: 0x9d0cc, func: __sys_numa_getaffinity
lib/libc.so.7: off: 0x9d0ec, func: _procctl
...

feynman% readelf -r lib/libc.so.7 | grep 9d0ac
00000009d0ac 09ab00000002 R_X86_64_PC32 00000000001a62c4 .cerror + fffffffffffffffc

These all come from the autogenerated libc syscall wrappers.

#define RSYSCALL(name) ENTRY(_sys##name); \
WEAK_REFERENCE(_sys##name, name); \
WEAK_REFERENCE(_sys##name, ##name); \
mov $SYS##name,%eax; KERNCALL; \
jb HIDENAME(cerror); ret; \
END(_sys##name)